Atlanta Geological Society Newsletter

ODDS AND ENDS Dear AGS members, January Meeting

Like that, it’s on into a new year. While that Join us Tuesday, January 29, 2019 at makes a difference to human endeavors, it is so the Fernbank Museum of Natural inconsequential geologically. My recent trip to History, 760 Clifton Road NE, Atlanta the Scotland only emphasized that more. After I GA. The social/dinner starts at 6:30 pm worked on my talk for last November, I ran and the meeting starts at approximately across a TV series from the BBC called Men of Rock. No, its not about Jimmy Page but rather 7 p.m. the mostly Scottish men who laid the historical foundation for geology. This is right up my This month out presentation is alley. There are three episodes presented by Dr. “Investigating Rare Biomineralization Ian Stewart and available free on YouTube. Structures in Trilobites” While viewing, you might get the impression presented by Ms. Raya Greenberger that only the Scots were doing any geology at Please find more information about the that time. That aside, I do believe it would be presentation and Ms. Greenbergerger’s worth your time as there’s great scenes and bio on the next page. scenery. Just about a month ago, there was an earthquake in East Tennessee. While a magnitude of 4.3 is Please come out, enjoy a bite to not big on a worldwide scale, it was big for the eat, the camaraderie, an interesting East. As the result of a Google search on Atlanta presentation and perhaps some and geology, I was contacted by a local TV discussion on the importance of station to give some technical background. My accurate mineral characterization and 20 seconds of fame evaporated quickly but I biomineralization of fossils. have added a ‘Volcanoes and Earthquake’ app to my phone. It is both fun and amazing to be able to know that there was an earthquake in New www.atlantageologicalsociety.org Zealand 37 minutes ago. BTW, our dues renew on a calendar basis. I just facebook.com/Atlanta-Geological- went to our website, followed the links and it Society took less than 2 minutes to be paid in full. Hope to see you on the 29th. Ben Bentkowski, President 2019 AGS Dues Renew This Month

AGS January 2019 Page 2

AGS January 2019 Page 3

Middle East Fossils Push Back Origin of Key Plant Groups Millions

of Years

Paleobotanists exploring a site near the Dead Sea have unearthed a startling connection between today's conifer forests in the Southern Hemisphere and an unimaginably distant time torn apart by a global cataclysm. Exquisitely preserved plant fossils show the podocarps, a group of ancient evergreens that includes the massive yellowwood of South Africa and the red pine of New Zealand, thrived in the Permian period, more than 250 million years ago. That's tens of millions of years earlier than thought, and it shows that early podocarps survived the "great dying" at the end of the Permian, the worst mass extinction the planet has ever known.

Reported in this week's issue of Science, the fossils push back the origins not just of podocarps, but also of groups of seed ferns and cycadlike plants. Beyond altering notions of plant evolution, the discoveries lend support to a 45-year-old idea that the tropics serve as a "cradle" of evolution. "This is an exciting paper," says Douglas Soltis, a plant evolutionary biologist at the University of Florida (UF) in Gainesville. By revealing the richness of the Permian tropics, he adds, "The findings may also help researchers decide where to look for crucial fossil discoveries."

During the Permian, from 299 million to 251 million years ago, Earth's landmasses had merged to form a supercontinent, bringing a cooler, drier climate. Synapsids, thought to be ancient predecessors of mammals, and sauropsids, ancestors to reptiles and birds, roamed the landscape. Simple seed-bearing plants had already appeared on the scene. Family trees reconstructed from the genomes of living plants suggest more sophisticated plant groups might also have evolved during the Permian, but finding well-preserved plant fossils from that time has been difficult.

About 50 years ago, a German geologist described the Umm Irna formation, a series of sedimentary layers exposed along the Jordanian coast of the Dead Sea. Working at the site in the early 2000s, paleontologist Abdalla Abu Hamad, now with the University of Jordan in Amman, discovered some exquisitely preserved plants from Permian swamps and drier lowlands.

After moving to the University of Münster in Germany for a Ph.D., he teamed up with paleobotanists there to analyze hundreds of newly collected plant fossils, including leaves, stems, and reproductive organs. Many of the fossils preserve the ancient plants' cuticle, a waxy surface layer that captures fine features, such as the leaf pores called stomata. That made it possible for the team to positively identify many of the plants.

"At first, we couldn't really believe our eyes," Benjamin Bomfleur, a study co-author at the University of Münster, recalls. Many were plants thought have gotten their start later in the Mesozoic, the period when dinosaurs ruled. Along with the podocarps, they identified corystosperms, seed ferns common in the dinosaur age but extinct now, and cycadlike Bennettitales, another extinct group that had flowerlike reproductive structures.

Such finds could help resolve an ongoing debate about why the tropics have more species than colder latitudes do. Some have suggested that species originate at many latitudes but are more likely to diversify in the tropics, with its longer growing seasons, higher rainfall and temperatures, and other features. But another theory proposes that most plant—and animal—species actually got their start near the equator, making the low latitudes an evolutionary "cradle" from which some species migrate north and south. The new work "supports the idea of the evolution cradle," Bomfleur says. Philip Mannion, a paleontologist at Imperial College London agrees, but says the case is not fully settled. "Our sampling of the fossil record is extremely

Page 4 AGS January 2019

Middle East Fossils Push Back Origin of Key Plant Groups Millions of Years (Continued)

Freed from rock by a strong acid, this fossilized frond preserves enough detail to identify it as a seed fern.

It's not clear how the newfound Permian plants made it through the great dying, a 100,000-year period when, for reasons that are still unclear, 90% of marine life and 70% of life on land disappeared. But their presence in the Permian raises the possibility that other plant groups thought to have later origins actually emerged then in the tropics, says UF plant evolutionary biologist Pamela Soltis. If these select plants survived the mass extinction, she says, "Perhaps the communities they supported may have been more stable as well."

Read more about this article at: http://www.sciencemag.org/news/2018/12/middle-east-fossils-push-back-origin-key-plant-groups-millions-years

Ancient Steroids Establish the Ediacaran Fossil Dickinsonia as One of The Earliest Animals

Abstract The enigmatic Ediacara biota (571 million to 541 million years ago) represents the first macroscopic complex organisms in the geological record and may hold the key to our understanding of the origin of animals. Ediacaran macrofossils are as “strange as life on another planet” and have evaded taxonomic classification, with interpretations ranging from marine animals or giant single-celled protists to terrestrial lichens. Here, we show that lipid biomarkers extracted from organically preserved Ediacaran macrofossils unambiguously clarify their phylogeny. Dickinsonia and its relatives solely produced cholesteroids, a hallmark of animals. Our results make these iconic members of the Ediacara biota the oldest confirmed macroscopic animals in the rock record, indicating that the appearance of the Ediacara biota was indeed a prelude to the Cambrian explosion of animal life.

The Ediacara biota remains one of the greatest mysteries in paleontology. Members of this assemblage were initially described as animals; however, as collections grew, it became apparent that Ediacaran fossils and their body plans are difficult to compare with modern phyla. A major complication for the study of Ediacaran organisms is their soft-bodied nature and particular mode of preservation, rarely found in younger fossils. Thus, the interpretation of various members of the Ediacara biota has crossed several Kingdoms and Domains, ranging from bacterial colonies, marine fungi, lichens, and giant protists to stem-group animals and crown-group Eumetazoa. The recent general consensus is that these fossils are polyphyletic: At least

Page 5 AGS January 2019

Ancient Steroids Establish the Ediacaran Fossil Dickinsonia as One

of The Earliest Animals (Continued) some members of the Ediacara biota are almost unanimously interpreted as bilaterian animals (Kimberella), whereas others are confidently ascribed to giant protozoa (Palaeopascichnus). Beltanelliformis—although previously interpreted as bacteria, benthic and planktonic algae, as well as different animals—is now recognized as a spherical colony of cyanobacteria on the basis of their biomarker content. The affinity of most other Ediacarans, however, remains controversial, even at the Kingdom level. Most recently, arguments surrounding these fossils have centered on lichens, giant protists, and stem- or crown-group Metazoa.

Whereas the lichen hypothesis requires an implausible reinterpretation of the habitat of the Ediacara biota from a marine to a continental depositional environment, for many Ediacaran fossils, including dickinsoniids, it currently seems impossible to distinguish between giant protist and metazoan origins. Some Ediacaran fossils, such as Palaeopascichnus, were likely giant unicellular eukaryotes (protists), which means that in contrast to modern ecosystems, these organisms were present and sometimes extremely abundant in shallow- water Ediacaran habitats. Features of dickinsoniids such as “quilting” patterns, the inferred absence of dorso- ventral differentiation, and putative external digestion mode were found to be compatible with modern giant protists and hard to reconcile with metazoans. Some modern giant protists can be up to 25 cm in size. In the absence of metazoan competition, they may have become even larger, possibly providing an explanation for the size range of Ediacaran protistan fossils. Some giant protists even have a motile lifestyle, compatible with Ediacaran trace fossils and dickinsoniid “footprints”. For dickinsoniids, the absence of evidence for a mouth and gut, perceived absence of bilateral symmetry, and possible external digestion are all consistent with a protistan origin. However, all of the above characteristics are also compatible with basal Metazoa such as the Placozoa that are situated at the very base of Eumetazoa, whereas rejection of an external digestion mode and acceptance of supposed cephalization may place dickinsoniids even higher on the metazoan tree. The nature of dickinsoniids, and most other Ediacaran fossils, thus remains unresolved.

We applied a new approach to test the lichen, protist, and animal hypotheses by studying biomarkers extracted from organically preserved dickinsoniids. Hydrocarbon biomarkers are the molecular fossils of lipids and other biological compounds. Encased in sedimentary rock, biomarkers may retain information about their biological origins for hundreds of millions of years. For instance, hopanes are the hydrocarbon remains of bacterial hopanepolyols, whereas saturated steranes and aromatic steroids are diagenetic products of eukaryotic sterols. The most common sterols of Eukarya possess a cholesteroid, ergosteroid, or stigmasteroid skeleton with 27, 28, or 29 carbon atoms, respectively. These C27 to C29 sterols, distinguished by the alkylation pattern at position C-24 in the sterol side chain, function as membrane modifiers and are widely distributed across extant Eukarya, but their relative abundances can give clues about the source organisms. Apart from Dickinsonia (Figure. 1B), which is one of the most recognizable Ediacaran fossils, dickinsoniids include Andiva (Figure. 1C and Figure. S1), Vendia, Yorgia, and other flattened Ediacaran organisms with segmented metameric bodies and a median line along the body axes, separating the “segments.” The specimens for this study were collected from two surfaces in the Lyamtsa (Dickinsonia) and Zimnie Gory (Andiva) localities of the Ediacara biota in the White Sea region (Russia). Both Dickinsonia and Andiva are preserved in negative hyporelief on the sole of sandstones with microbial mat impressions and consist of a thin (up to ~3 μm) film of organic matter. The organic matter was detached from the rock surface (fig. S1) and extracted for hydrocarbon biomarkers under strict exclusion of contamination (materials and methods). Much thinner organic films covering the surfaces around Andiva fossils from the Zimnie Gory locality were extracted as well, providing a background signal coming from associated microbial mats. Investigation of biomarker composition of surrounding surfaces and enclosing sedimentary rocks allowed us not only to

Page 6 AGS January 2019

Ancient Steroids Establish the Ediacaran Fossil Dickinsonia as One of The Earliest Animals (Continued) subtract the background signal but also to make sure that the biomarker signal from the fossils is not contaminated (supplementary text). We analyzed biomarkers using gas chromatography–mass spectrometry (materials and methods).

Figure. 1 Biomarkers from organically preserved Dickinsonia.

(A) Mass/charge ratio 253 selected ion recording chromatogram showing the distribution of monoaromatic steroids (MAS) of the solvent extract of a large Dickinsonia specimen (Dickinsonia-2; 5.5 cm width). (B) Organically preserved Dickinsonia from the Lyamtsa locality (Dickinsonia-2). (C) Metastable reaction monitoring chromatogram showing the sum of C27–29 sterane traces of Dickinsonia-2. αββ = 5α(H), 14β(H), 17β(H) (and correspondingly for ααα and βαα); S and R indicate isomerization at position C-20. (D) Relationship between the MAS C27/MAS C29 ratio and the Animal Decomposition Index (ADI) = (C27 5β/5α)/(C295β/5α) in Dickinsonia (n = 6 samples), Andiva (n = 2 samples), and bulk rock extracts from the Lyamtsa and Zimnie Gory localities (n = 32 samples). Only samples with detectable MAS were used in the plot. ADI is a measure of the quantity of sterols that decomposed in the anaerobic microenvironment of an animal carcass relative to normal sterol decomposition within the background sediment. ADI ≈ 1 indicates that cholesteroids and stigmasteroids underwent alteration in the same diagenetic environment consistent with the absence of animal tissue. ADI > 1 indicates contribution of animal steroids to the biomarker signal. (E) Relationship between the 5β/5α sterane isomer ratio for cholestane (C27) and stigmastane (C29) in Dickinsonia (n = 8 samples), Andiva (n = 2 samples), and bulk rock extracts from the Lyamtsa and Zimnie Gory localities (n = 54 samples). 5β/5α = (βαα 20R + ααα 20S)/ααα 20R. MAS structures: I = 5β(H)10β(CH3), II = 5α(H)10β(CH3), V = 5β(CH3)10β(H), and VII = 5α(CH3)10α(H).

The striking abundance of cholesteroids in Dickinsonia is corroborated by an unusual sterane isomer distribution. In sediments surrounding the fossils in Lyamtsa and Zimnie Gory localities, the ratio of 5β over 5α stereoisomers for all steranes is generally near the equilibrium diagnostic for abiological isomerization (average 5β/5α = 0.65 ± 0.26, n = 54 samples) (Figure. 1, D and E). By contrast, in the fossils, 5β/5α of cholestane is markedly elevated—up to 5.5 in Dickinsonia (Table 1and Figure. 1, C, D, and E)—values that are generated through strictly anaerobic microbial activity, such as during the decay of carcasses. Although the gut flora of some mammals is known to produce 5β-stanols (precursors of 5β-steranes), high relative abundances of these molecules in some background sediments (Figure. 1E) and macroalgae from the White Sea contests the otherwise exciting possibility that 5β-steranes originated from Dickinsonia’s gut microbiota (supplementary text). 5β ergostanes and stigmastanes in the Dickinsonia extracts are not elevated (Table 1), demonstrating that they are ultimately not derived from dickinsoniids but from the underlying microbial mat or surrounding sediment (fig. S2). On the basis of these steroid homolog and isomer patterns, we compute that the sterols of living Dickinsonia consisted of at least 99.7% cholesteroids (supplementary text). Within analytical precision, it is impossible to exclude that Dickinsonia produced traces of ergosteroids (up to 0.23%) or stigmasteroids (up to 0.07%). Such steroids, if present, may be derived from the organism itself but could also represent dietary uptake or contributions from symbionts.

Biomarker signatures of Andiva specimens from the Zimnie Gory locality are less well differentiated from the

AGS January 2019 Page 7

Ancient Steroids Establish the Ediacaran Fossil Dickinsonia as One

of The Earliest Animals (Continued) microbial mat background signal and do not display a clear elevation of cholesteroids relative to the background (Table 1). Yet even in these fossils, 5β/5α ratios for cholestanes are much higher (5β/5α = 1.02 to 1.31) when compared with ergostanes and stigmastanes from the fossil extract (5β/5α = 0.52 to 0.66) and the surrounding mat (5β/5α = 0.65 to 0.81) (Table 1). On the basis of these values, we can compute a conservative minimum C27sterol content of 88.1% for Andiva (supplementary text).

Using the remarkable steroid patterns of the fossils, it is possible to test the position of dickinsoniids on the phylogenetic tree. Lichen-forming fungi only produce ergosteroids, and even in those that host symbiotic algae, ergosteroids remain the major sterols. Dickinsoniacontained no or a maximum of only 0.23% ergosteroids, conclusively refuting the lichen hypothesis (7). The groups of rhizarian protists that include gigantic representatives (Gromiidae, Xenophyophorea, and other Foraminifera) and their retarian relatives all produce a complex mixture of sterols, with cholesteroids comprising 10.3 to 78.2% of the mixture, ergosteroids 4.9 to 43.0%, and stigmasteroids 7.2 to 60.1% (table S4). Moreover, rhizarian protists may produce C30sterols (24-n-propylcholesteroids) that can form a notable (up to ~20%) proportion of their total sterol content. By contrast, in most Dickinsonia and Andiva extracts, C30 steroids were below detection limits. Thus, the steroid composition of dickinsoniids is markedly distinct from steroid distributions observed in Rhizaria, rendering a protozoan affinity of these fossils extremely unlikely. All animals—with rare exceptions, such as some demosponges and bivalve molluscs—are characterized by exclusive production of C27 sterols. The closest relatives of metazoans, Choanoflagellatea and Filasterea, produce 90 to 100% and 84 to 100% of cholesterol, respectively, and contain up to 16% ergosteroids. Although the sterol composition of some choanoflagellates and filastereans falls within the range observed for Dickinsonia and Andiva, they are unlikely precursor candidates because these groups are only ever represented by microscopic organisms, leaving a stem- or crown-group metazoan affinity as the only plausible phylogenetic position for Dickinsonia and its morphological relatives.

Molecular fossils firmly place dickinsoniids within the animal kingdom, establishing Dickinsonia as the oldest confirmed macroscopic animals in the fossil record (558 million years ago) next to marginally younger Kimberella from Zimnie Gory (555 million years ago). However alien they looked, the presence of large dickinsoniid animals, reaching 1.4 m in size, reveals that the appearance of the Ediacara biota in the fossil record is not an independent experiment in large body size but indeed a prelude to the Cambrian explosion of animal life.

Read more about this article at: http://science.sciencemag.org/content/361/6408/1246 Dueling Spacecraft Look Deep Into Saturn and Jupiter

A clever use of radio signals from planetary spacecraft is allowing researchers to pierce the swirling clouds that hide the interiors of Jupiter and Saturn, where crushing pressure transforms matter into states unknown on Earth. The effort, led by Luciano Iess of Sapienza University in Rome, turned signals from two NASA probes, Cassini at Saturn and Juno at Jupiter, into probes of gravitational variations that originate deep inside these gas giants.

What the researchers have found is fueling a high-stakes game of compare and contrast. The results, published last year in Nature for Jupiter and this week in Science for Saturn, show that “the two planets are more complex than we thought,” says Ravit Helled, a planetary scientist at the University of Zurich in Switzerland. “Giant planets are not simple balls of hydrogen and helium.”

Page 8 AGS January 2019

Dueling Spacecraft Look Deep Into Saturn and Jupiter (Continued)

In the 1980s, Iess helped pioneer a radio instrument for Cassini that delivered an exceptionally clear signal because it worked in the Ka band, which is relatively free of noise from interplanetary plasma. By monitoring fluctuations in the signal, the team planned to search for gravitational waves from the cosmos and test general relativity during the spacecraft's journey to Saturn, which began in 1997. Iess's group put a similar device on Juno, which launched in 2011, but this time the aim was to study Jupiter's interior.

Juno skims close to Jupiter's surface every 53 days, and with each pass hidden influences inside the planet exert a minute pull on the spacecraft, resulting in tiny Doppler shifts in its radio signals. Initially, Iess and his team thought measuring those shifts wouldn't be feasible at Saturn because of the gravitational influence of its rings. But that obstacle disappeared earlier this decade, after the Cassini team decided to end the mission by sending the craft on a series of orbits, dubbed the Grand Finale, that dipped below the rings and eliminated their effects. As a result, Iess and colleagues could use radio fluctuations to map the shape of gravity fields at both planets, allowing them to infer the density and movements of material deep inside.

One goal was to probe the roots of the powerful winds that whip clouds on the gas giants into distinct horizontal bands. Scientists assumed the winds would either be shallow, like winds on Earth, or very deep, penetrating tens of thousands of kilometers into the planets, where extreme pressure is expected to rip the electrons from hydrogen, turning it into a metallike conductor. The results for Jupiter were a puzzle: The 500- kilometer-per-hour winds aren't shallow, but they reach just 3000 kilometers into the planet, some 4% of its radius. Saturn then delivered a different mystery: Despite its smaller volume, its surface winds, which top out at 1800 kilometers per hour, go three times deeper, to at least 9000 kilometers. “Everybody was caught by surprise,” Iess says.

Scientists think the explanation for both findings lies in the planets' deep magnetic fields. At pressures of about 100,000 times that of Earth's atmosphere—well short of those that create metallic hydrogen—hydrogen partially ionizes, turning it into a semiconductor. That allows the magnetic field to control the movement of the material, preventing it from crossing the field lines. “The magnetic field freezes the flow,” and the planet becomes rigid, says Yohai Kaspi, a planetary scientist at the Weizmann Institute of Science in Rehovot, Israel, who worked with Iess. Jupiter has three times Saturn's mass, which causes a far more rapid increase in atmospheric pressure—about three times faster. “It's basically the same result,” says Kaspi, but the rigidity sets in at a shallower depth.

The Juno and Cassini data yield only faint clues about greater depths. Scientists once believed the gas giants formed much like Earth, building up a rocky core before vacuuming gas from the protoplanetary disc. Such a stately process would have likely led to distinct layers, including a discrete core enriched in heavier elements. But Juno's measurements, interpreted through models, suggested Jupiter's core has only a fuzzy boundary, its heavy elements tapering off for up to half its radius. This suggests that rather than forming a rocky core and then adding gas, Jupiter might have taken shape from vaporized rock and gas right from the start, says Nadine Nettelmann, a planetary scientist at the University of Rostock in Germany.

The picture is still murkier for Saturn. Cassini data hint that its core could have a mass of some 15 to 18 times that of Earth, with a higher concentration of heavy elements than Jupiter's, which could suggest a clearer boundary. But that interpretation is tentative, says David Stevenson, a planetary scientist at the California Institute of Technology in Pasadena and a coinvestigator on Juno. What's more, Cassini was tugged by something deep within Saturn that could not be explained by the winds, Iess says. “We call it the dark side of Saturn's gravity.” Whatever is causing this tug, Stevenson adds, it's not found on Jupiter. “It is a major result. I don't think we understand it yet.”

AGS January 2019 Page 9

Dueling Spacecraft Look Deep Into Saturn and Jupiter (Continued)

Material thousands of kilometers below the clouds of Jupiter and Saturn tugs subtly on orbiting spacecraft, revealing hidden structure and motions.

Because Cassini's mission ended with the Grand Finale, which culminated with the probe's destruction in Saturn's atmosphere, “There's not going to be a better measurement anytime soon,” says Chris Mankovich, a planetary scientist at the University of California, Santa Cruz. But although the rings complicated the gravity measurements, they also offer an opportunity. For some unknown reason—perhaps its winds, perhaps the pull of its many moons—Saturn vibrates. The gravitational influence of those oscillations minutely warps the shape of its rings into a pattern like the spiraling arms of a galaxy. The result is a visible record of the vibrations, like the trace on a seismograph, which scientists can decipher to plumb the planet. Mankovich says it's clear that some of these vibrations reach the deep interior, and he has already used “ring seismology” to estimate how fast Saturn's interior rotates.

Cassini's last gift may be to show how fortunate scientists are to have the rings as probes. Data from the spacecraft's final orbits enabled Iess's team to show the rings are low in mass, which means they must be young, as little as 10 million years old—otherwise, encroaching interplanetary soot would have darkened them. They continue to rain material onto Saturn, the Cassini team has found, which could one day lead to their demise. But for now, they stand brilliant against the gas giant, with more stories to tell.

Read more about this article at: http://science.sciencemag.org/content/363/6424/214

NASA's Moon Data Sheds Light on Earth’s Asteroid Impact History By looking at the Moon, the most complete and accessible chronicle of the asteroid collisions that carved our young solar system, a group of scientists is challenging our understanding of a part of Earth’s history.

The number of asteroid impacts to the Moon and Earth increased by two to three times starting around 290 million years ago, researchers reported in a January 18 paper in the journal Science. They could tell by creating the first comprehensive timeline of large craters on the Moon formed in the last billion years by using images and thermal data collected by NASA’s Lunar Reconnaissance Orbiter (LRO). When the scientists compared those to the timeline of Earth’s craters, they found the two bodies had recorded the same history of asteroid bombardment—one that contradicts theories about Earth’s impact rate.

For decades, scientists have tried to understand the rate that asteroids hit the Earth by carefully studying impact craters on continents and by using radiometric dating of the rocks around them to determine the ages of the largest, and thus most intact, ones. The problem is that many experts assumed that early Earth craters have been worn away by wind, storms, and other geologic processes. This idea explained why Earth has fewer older craters than expected compared to other bodies in the solar system, but it made it difficult to find an accurate impact rate and to determine whether it had changed over time.

Page 10 AGS January 2019

NASA's Moon Data Sheds Light on Earth’s Asteroid Impact History (Continued)

NASA’s Landsat 7 satellite captured this image of Pingualuit Crater on August 17, 2002. In it, water appears blue, and land appears in varying shades of beige. With a diameter of 2.14 miles (3.44 kilometers), Pingualuit Crater holds a lake about 876 feet (267 meters) deep.

A way to sidestep this problem is to examine the Moon. Earth and the Moon are hit in the same proportions over time. In general, because of its larger size and higher gravity, about twenty asteroids strike Earth for every one that strikes the Moon, though large impacts on either body are rare. But even though large lunar craters have experienced little erosion over billions of years, and thus offer scientists a valuable record, there was no way to determine their ages until the Lunar Reconnaissance Orbiter started circling the Moon a decade ago and studying its surface.

“We’ve known since the Apollo exploration of the Moon 50 years ago that understanding the lunar surface is critical to revealing the history of the solar system,” said Noah Petro, an LRO project scientist based at NASA Goddard Space Flight Center in Greenbelt, Maryland. LRO, along with new commercial robotic landers under development with NASA, said Petro, will inform the development and deployment of future landers and other exploration systems needed for humans to return to the Moon's surface and to help prepare the agency to send astronauts to explore Mars. Achieving NASA’s exploration goals is dependent on the agency’s science efforts, which will contribute to the capabilities and knowledge that will enable America’s Moon to Mars exploration approach now and in the future.

“LRO has proved an invaluable science tool," said Petro. "One thing its instruments have allowed us to do is peer back in time at the forces that shaped the Moon; as we can see with the asteroid impact revelation, this has led to groundbreaking discoveries that have changed our view of Earth.” The Moon as Earth's Mirror LRO's thermal radiometer, called Diviner, has taught scientists how much heat is radiating off the Moon’s surface, a critical factor in determining crater ages. By looking at this radiated heat during the lunar night, scientists can calculate how much of the surface is covered by large, warm rocks, versus cooler, fine-grained regolith, also known as lunar soil.

AGS January 2019 Page 11

NASA's Moon Data Sheds Light on Earth’s Asteroid Impact History (Continued)

A 2014 Lunar Reconnaissance Orbiter Camera image showing two similarly sized craters in Mare Tranquillitatis. Both are about 500 meters in diameter. One is littered with boulders and the other is not. This boulder discrepancy is likely due to age differences between the two craters. Image width is about 2 kilometers.

Large craters formed by asteroid impacts in the last billion years are covered by boulders and rocks, while older craters have few rocks, Diviner data showed. This happens because impacts excavate lunar boulders that are ground into soil over tens to hundreds of millions of years by a constant rain of tiny meteorites.

Paper co-author Rebecca Ghent, a planetary scientist at University of Toronto and the Planetary Science Institute in Tucson, Arizona, calculated in 2014 the rate at which Moon rocks break down into soil. Her work thus revealed a relationship between an abundance of large rocks near a crater and the crater’s age. Using Ghent’s technique, the team assembled a list of ages of all lunar craters younger than about a billion years. “It was a painstaking task, at first, to look through all of these data and map the craters out without knowing whether we would get anywhere or not,” said Sara Mazrouei, the lead author of the Science paper who collected and analyzed all the data for this project while a Ph.D. student at the University of Toronto.

The work paid off, returning several unexpected findings. First, the team discovered that the rate of large crater formation on the Moon has been two to three times higher over approximately the last 290 million years than it had been over the previous 700 million years. The reason for this jump in the impact rate is unknown. It might be related to large collisions taking place more than 300 million years ago in the main asteroid belt between the orbits of Mars and Jupiter, the researchers noted. Such events can create debris that can reach the inner solar system.

The second surprise came from comparing the ages of large craters on the Moon to those on Earth. Their similar number and ages challenges the theory that Earth had lost so many craters through erosion that an impact rate could not be calculated.

Page 12 AGS January 2019

NASA's Moon Data Sheds Light on Earth’s Asteroid Impact History (Continued) “The Earth has fewer older craters on its most stable regions not because of erosion, but because the impact rate was lower about 290 million years ago,” said William Bottke, an asteroid expert at the Southwest Research Institute in Boulder, Colorado and a co-author of the paper. “This meant the answer to Earth’s impact rate was staring everyone right in the face.” Proving that fewer craters meant fewer impacts—rather than loss through erosion—posed a formidable challenge. Yet the scientists found strong supporting evidence for their findings through a collaboration with Thomas Gernon, an Earth scientist based at the University of Southampton in England who works on a terrestrial feature called kimberlite pipes.

These underground pipes are long-extinct volcanoes that stretch, in a carrot shape, a couple of kilometers below the surface. Scientists know a lot about the ages and rate of erosion of kimberlite pipes because they are widely mined for diamonds. They also are located on some of the least eroded regions of Earth, the same places we find preserved impact craters. Gernon showed that kimberlite pipes formed since about 650 million years ago had not experienced much erosion, indicating that the large impact craters younger than this on stable terrains must also be intact. “So that's how we know those craters represent a near-complete record,” Ghent said.

Ghent’s team, which also included Southwest Research Institute planetary astronomer Alex Parker, wasn’t the first to propose that the rate of asteroid strikes to Earth has fluctuated over the past billion years. But it was the first to show it statistically and to quantify the rate. Now the team’s technique can be used to study the surfaces of other planets to find out if they might also show more impacts.

The team’s findings related to Earth, meanwhile, may have implications for the history of life, which is punctuated by extinction events and rapid evolution of new species. Though the forces driving these events are complicated and may include other geologic causes, such as large volcanic eruptions, combined with biological factors, the team points out that asteroid impacts have surely played a role in this ongoing saga. The question is whether the predicted change in asteroid impacts can be directly linked to events that occurred long ago on Earth.

Read more about this article at: https://www.nasa.gov/feature/goddard/2019/scientists-find-increase-in-asteroid-impacts-on-ancient-earth-by- studying-the-moon

Earth and Moon Impact Flux Increased at The End of The Paleozoic

Abstract The terrestrial impact crater record is commonly assumed to be biased, with erosion thought to eliminate older craters, even on stable terrains. Given that the same projectile population strikes Earth and the Moon, terrestrial selection effects can be quantified by using a method to date lunar craters with diameters greater than 10 kilometers and younger than 1 billion years. We found that the impact rate increased by a factor of 2.6 about 290 million years ago. The terrestrial crater record shows similar results, suggesting that the deficit of large terrestrial craters between 300 million and 650 million years ago relative to more recent times stems from a lower impact flux, not preservation bias. The almost complete absence of terrestrial craters older than 650 million years may indicate a massive global-scale erosion event near that time.

The abundance of terrestrial craters with diameters (D) ≥ 20 km decreases substantially with age. A common assumption is that this loss is driven by erosive and tectonic processes operating over hundreds of millions of years. Unfortunately, it is challenging to quantitatively test this hypothesis with existing terrestrial data. An

AGS January 2019 Page 13

Earth and Moon Impact Flux Increased at The End of The Paleozoic (Continued) alternative is to estimate terrestrial crater loss rates by comparing Earth’s crater record with the Moon’s. Earth and the Moon have been struck by the same impactor population over time, but large lunar craters have experienced limited degradation over billions of years. An obstacle to performing this test has been obtaining accurate dates for large lunar craters.

We used an analysis of the thermophysical characteristics of lunar impact ejecta as measured with the Diviner thermal radiometer on NASA’s Lunar Reconnaissance Orbiter (LRO) (1, 2) to estimate the ages of lunar craters with D >10 km and younger than 1 billion years (Ga). The formation of large lunar craters excavates numerous ≥1m ejecta fragments onto the Moon’s surface. These recently exposed rocks have high thermal inertia and remain warm during the lunar night relative to the surrounding lunar soils (called regolith), which have low thermal inertia. The nighttime temperatures were calculated from three of Diviner’s thermal infrared channels. Rock abundance values, defined as the fractional coverage of a Diviner pixel by exposed meter- scale rocks (Figure. 1), were obtained, simultaneously with rock-free lunar regolith temperatures, by exploiting the fact that a mixture of lunar rocks and regolith produces a mixed spectral radiance and therefore different estimates of brightness temperature in each of the three thermal infrared channels.

Figure. 1 Regression of lunar crater age versus 95th percentile rock abundance. Data point labels correspond to dated lunar craters listed in table S1. Rock cover is defined as materials with rocklike thermal inertia and minimum diameters larger than the diurnal thermal skin depth (~0.5 m). This regression differs from previous analysis because of use of an updated rock abundance dataset and an updated age for Aristarchus crater, together with a statistical treatment that marginalizes over unacknowledged uncertainties for the published crater ages. Red error bars illustrate uncertainties for each crater, and black error bars show the uncertainties implied by the median value of the uncertainty scaling factor c given its posterior PDF (eq. S2). The best fitting parameters in b the relation RA95/5 = a × (age/Ma) are a, 0.33; b, –0.50 (black solid curve); black dashed and dotted curves indicate the 68 and 95% credible intervals. After propagation through the joint terrestrial/lunar Approximate Bayesian Computation rejection (ABCr) analysis, the best fitting parameters are a, 0.34; b, –0.51 (cyan solid curve); cyan dashed and dotted curves show the 68 and 95% credible intervals. (Insets) The two-dimensional (2D) distribution of the posterior PDF sample of parameters (a, b) before and after ABCr analysis (black and cyan points, respectively), their marginalized distributions, and p(c), the 1D marginalized posterior PDF of the uncertainty scaling factor c (eq. S2).

Using these data, an inverse relationship between rock abundance in large crater ejecta and crater age has been demonstrated by calculating ejecta rock abundance values for nine “index” craters with independently determined ages. Young craters were found to have high rock abundance in their ejecta, whereas rock abundance decreases with increasing crater age, eventually becoming indistinguishable from the background for craters older than ~1 Ga. The breakdown of lunar rocks has most likely occurred at a steady rate over the past billion years through the constant influx of tiny impactors and the thermal effects of lunar day-night cycling. We derived a crater age–rock abundance regression function shown in Figure. 1 and Figure. S1.

Page 14 AGS January 2019

Earth and Moon Impact Flux Increased at The End of The Paleozoic (Continued)

We identified 111 rocky craters on the Moon with D ≥10 km between 80°N and 80°S, with ejecta blankets that have rock abundance values high enough to distinguish them from the background regolith (Figure. 2A and table S1). We used the 95th percentile rock abundance values (RA95/5), which are those that separate the upper 5% from the lower 95% of RA values for a given crater’s ejecta. We chose 10 km as a minimum size for this analysis because those craters have penetrated the surface regolith deeply enough to have excavated large blocks from the underlying bedrock. This approach minimizes the influence of variations in original ejecta block population that are due to spatial variations in surface soil thickness.

Figure. 2 Geographic and SFD of rocky lunar craters. (A) Geographic distribution of 111 rocky (young) craters with D ≥ 10 km between 80°N and 80°S on the Moon (listed in table S1), scaled by size and color coded according to age. Orange (dark yellow deuteranopia) indicates craters younger than 290 Ma; pink (light blue deuteranopia) indicates craters 290 to 580 Ma old; dark blue indicates craters 580 to 870 Ma old; yellow indicates craters 870 to 1160 Ma old; and white indicates craters older than 1160 Ma. [Background image is from https://astrogeology.usgs.gov/search/map/Moon/LRO/LROC_WAC/Lunar_LRO_LROC- WAC_Mosaic_global_100m_June2013 (27)]. (B) Cumulative SFDs of craters. Red indicates average SFD of craters older than 290 Ma (55 craters; average of cumulative distribution in three age bins: 290 to 580 Ma old; 580 to 870 Ma old; and 870 to 1160 Ma old), black indicates craters younger than 290 Ma (56 craters), and error bars show Poisson noise. The lunar cratering rate has increased by a factor of 2.6 in the past 290 Ma compared with the preceding ~710 Ma.

Using Figure. 1, we calculated ages for these craters and found that they were not formed uniformly with time (Figure. 2B). This implies that the small- and large-body impact fluxes striking the Moon are probably decoupled from one another at a modest level, with small impactors more likely to maintain a steady impact flux than large impactors (Figure. S2). Our analysis also showed no statistical evidence for a leading versus trailing hemisphere asymmetry in the calculated ages of these large craters, nor for a latitudinal dependence in rocky crater abundance, although our relatively small sample size might make such a trend difficult to detect. We also identified no correlation between crater sizes and crater ages, meaning differently sized craters are randomly distributed in time.

To quantify the change in flux exhibited by these lunar craters, we adopted a piecewise-constant rate model in which a uniform cratering rate at early times changes instantaneously to a different rate at later times. Sampling from among all possible values of the crater age–rock abundance regression parameters, using

AGS January 2019 Page 15

Earth and Moon Impact Flux Increased at The End of The Paleozoic (Continued) conservative estimates on the lunar index crater ages (Figure. 1), we found that this model shows statistical evidence for a break at some time between 220 and 770 Ma ago (95% credible intervals), with the peak of the marginalized probability density function (PDF) at a break age of 400 Ma (Figure. S1). The ratio of the crater rate after the break age to the prebreak rate is 2.1, with 95% credible interval values of 1.4 to 20.6.

Supporting evidence for an increase of a factor of 2 to 3 in the lunar impact flux since ~400 Ma ago may come from the ages and abundances of lunar impact spherules. Created by energetic cratering events, these glassy melt droplets have been identified in the regolith samples returned from the Apollo landing sites. Their age distribution is a potential proxy for the impact flux of larger bodies and suggests that the impact flux increased by a factor of 3.7 ± 1.2 over the past 400 Ma, which is in broad agreement with our results. However, the abundance of young impact spherules found in Apollo lunar regolith samples could be a bias. Lunar craters formed over the past 300 to 400 Ma may have also degraded faster by means of diffusion processes than those that formed between 700 and 3100 Ma ago. This observation may be explained if large impacts enhance diffusive processes through, for example, seismic shaking, and the large-body impact flux has increased over recent times.

Rayed lunar craters have previously been used to compute impact flux rates, with the assumption often made that they formed in the past 1 Ga. We found 11 farside rocky craters with D ≥ 20 km formed in the past 1 Ga, compared with 28 to 32 farside rayed craters assumed to be this age. This discrepancy suggests that rayed craters may have a much wider spread of ages than commonly thought (supplementary text).

These results for the Moon provide insights into Earth’s crater record. Interpretation of the terrestrial record is problematic because (i) an unknown number of older craters have been erased at unknown times by erosion or tectonics, (ii) stable continental surfaces capable of recording ancient impacts have potentially been buried and exhumed multiple times since they formed, (iii) it is difficult to precisely quantify which terrains have been adequately searched for craters, and (iv) not all craters are exposed at the surface but instead have to be identified through geophysical anomalies and explored through drilling.

Lunar craters have experienced comparatively little erosion over the past 1 Ga, and the proximity of Earth to the Moon implies that both have been struck by the same population of impactors. A comparison of records on both bodies therefore provides an opportunity to quantify terrestrial selection effects.

Contrary to our expectations, we found that the size-frequency distributions (SFDs) of the lunar and terrestrial craters for D ≥ 20 km, normalized by the total number of craters, are highly similar (Figure. S3A). We found no evidence for size bias in retention of terrestrial craters; in an average sense, for a given region, it appears that Earth either keeps all or loses all of its D ≥ 20 craters at the same rate, independent of size.

We compared the ages of the 38 known terrestrial craters with D ≥ 20 km (table S2) with the computed age distribution for lunar craters with D ≥ 10 and ≥ 20 km (Figure. 3 and table S1). Using the same statistical method for the terrestrial craters as for the lunar craters, we found that the terrestrial craters also have a break age and ratio of present-day to past crater rate close to lunar values (Figure. S1). Because there is evidence for a nonuniform terrestrial cratering rate similar to the lunar cratering rate and considering that Earth and the Moon share a similar bombardment history, we combined both records. The inclusion of terrestrial craters provides an absolute age chronology supplement to the nine index craters we have for the Moon. The model adopted to fit these data includes a single break between two uniform rates, but we do not rule out

Page 16 AGS January 2019

Earth and Moon Impact Flux Increased at The End of The Paleozoic (Continued)

Figure. 3 Age-frequency distributions of lunar and terrestrial craters. The lunar crater D ≥ 10 and 20 km curves are shown by the black line, whereas terrestrial craters with D ≥ 20 km (table S2) are shown with the red line. All terrestrial craters are younger than 650 Ma. The lunar impact flux increases by a factor of 2.6 near 290 Ma ago (Figure. S1). A simple piecewise model (cyan) demonstrates the break between two rates compared with a simple uniform model (dashed black). The similarity between the lunar and terrestrial distributions suggests that the inferred increase in terrestrial impacts is not a preservation bias.

other simple models (for example, cratering rate linearly increasing in time) or more complex models (for example, multiple breaks). Rather, we used the single-break piecewise model as a simple and physically plausible hypothesis to demonstrate that the lunar and terrestrial cratering rates have not been constant over the past billion years.

Our joint lunar and terrestrial analysis yields a ratio of the crater rate after the break age to the prebreak rate of 2.6, with a 95% credible interval value of 1.7 to 4.7. The most probable break age is 290 Ma. The impact rate change is reflected in the SFD curves, with craters younger than 290 Ma substantially higher in frequency at all diameters than those older than 290 Ma (Figure. 2B). The deficit of large terrestrial craters between 290 and 650 Ma old can therefore be interpreted to reflect a lower impact flux relative to the present day and not a bias (supplementary text).

The erosion history of Earth’s continents can also be constrained by using uranium-lead (U-Pb) thermochronology, or temperature-sensitive radiometric dating. Thermochronologic data suggest that stable continental terrains experience low erosion or burial rates of up to 2.5 m Ma−1, which equates to a maximum of 1.6 km vertical erosion (or deposition) over the past 650 Ma. This would likely be insufficient to eradicate craters with D ≥ 20 km, given that crater depths are approximately equal to ~10% of their original diameter.

Support for limited erosion on cratered terrains can also be found in the record of kimberlite pipes. Kimberlites are formed during explosive volcanism from deep mantle sources, generating carrot-shaped pipes 1 to 2 km deep (Figure. 4), and commonly preserve volcanic features (such as volcanic craters and pipes) that are depth-diagnostic. Impact craters and kimberlites are frequently found in common regions on stable continental surfaces (Figure. 4A), so kimberlites are a proxy that indicate the depth of erosion for surfaces of different ages. Deep erosion of stable continental surfaces (>2 km) should have removed most kimberlite pipes, leaving behind deep-seated intrusive rocks, but kimberlite pipes are relatively common throughout the Phanerozoic Eon (541 Ma ago to the present). Their spatiotemporal distribution (Figure. 4B) suggests only modest erosion (<1 km) on most cratons since 650 Ma ago, favoring the survival of D ≥ 20 km impact craters.

AGS January 2019 Page 17

Earth and Moon Impact Flux Increased at The End of The Paleozoic (Continued)

Figure. 4 Positions of terrestrial impact craters and kimberlites in space and time. (A) Locations of all impact craters identified in the Planetary and Space Science Centre (PASSC) Earth Impact Database, scaled by size and colored by age. Kimberlite occurrences are also shown; solid symbols denote those craters with well-defined ages (n = 624), and white diamonds indicate undated kimberlites (n = 3645). Gray regions correspond to major exposures of Precambrian basement rocks, which together with platform areas shown in beige form the stable cratons, where 84% of craters with D ≥ 20 km (and 84.6% of craters with D ≥ 10 km) occur. (B) Chronology of large impacts (>10 km) and well- dated kimberlites for each continent, excluding Antarctica. Colored symbols indicate depth-diagnostic kimberlite zones (labeled and illustrated in the inset). There is an abrupt cut-off in impact crater and kimberlite pipe frequency at ~650 Ma ago, which is coincident with Snowball Earth glaciation during the Cryogenian Period, 720 to 635 Ma ago.

There is a sharp cut-off in the number of terrestrial craters at ~650 Ma ago (Figures. 3 and 4). Given erosion rates on stable continental terrains after 650 Ma ago, similar conditions further back in time would have allowed most craters of Precambrian age (older than 541 Ma) to survive. Instead, the paucity of Precambrian craters is coincident with major episodes of globally extensive “Snowball Earth” glaciation (Figure. 4B). Pervasive subglacial erosion at ~650 to 720 Ma ago is thought to have removed kilometers of material from the continents, enough to erase most existing kimberlite pipes and impact craters (Figure. S5A). The exceptions are the D > 130 km impact craters Sudbury (1850 Ma ago) and Vredefort (2023 Ma ago). Both craters were deep enough to survive, but each shows indications of multiple kilometers of erosion.

The change in the lunar and terrestrial impact flux may be due to the breakup of one or more large asteroids in the inner and/or central main asteroid belt. Those located near dynamical resonances may produce long- lived surges in the impact flux as the fragments are slowly driven to escape routes by nongravitational forces. Asteroid evolution models suggest that the contribution of kilometer-sized impactors from a large parent-body disruption would have reached their new level within a few tens of millions of years of the breakup event(s), with the wave of bodies perhaps receding after hundreds of millions of years.

Read more about this article at: http://science.sciencemag.org/content/363/6424/253

East Antarctica’s Ice is Melting at an Unexpectedly Rapid Clip, New Study Suggests

Antarctica’s melting ice, which has caused global sea levels to rise by at least 13.8 millimeters over the past 40 years, was long thought to come from primarily one place: the unstable West Antarctic Ice Sheet. Now, scientists studying 40 years of satellite images have found that the East Antarctic Ice Sheet—considered

Page 18 AGS January 2019

East Antarctica’s Ice is Melting at an Unexpectedly Rapid Clip, New Study Suggests (Continued) largely insulated from the ravages of climate change—may also be melting at an accelerating rate. Those results, at odds with a large 2018 study, could dramatically reshape projections of sea level rise if confirmed. “If this paper is right, it changes the ball game for sea level rise in this century,” says Princeton University climate scientist Michael Oppenheimer, who was not involved in the new work. East Antarctica’s ice sheet holds 10 times the ice of its rapidly melting neighbor to the west.

The West Antarctic Ice Sheet, whose base is below sea level, has long been considered the most vulnerable to collapse. With an assist from gravity, a deep current of warm water slips beneath the sheet, melting it from below until it becomes a floating shelf at risk of breaking away. In contrast, frigid temperatures and a base mostly above sea level are thought to keep the East Antarctic Ice Sheet relatively safe from warm water intrusion. A collaboration of more than 60 scientists last year, published in Nature, estimated that the East Antarctic Ice Sheet actually added about 5 billion tons of ice each year from 1992 to 2017.

But as climate change shifts wind patterns around Antarctica, some scientists think warm water carried by a circular current off the continental shelf will start to invade East Antarctica’s once unassailable ice. “People who study Antarctic ice know that East Antarctica has the potential to start losing significant amounts of ice, but it’s never been clear how fast that would [happen],” Oppenheimer says.

To find out how fast that ice loss is happening, glaciologist Eric Rignot of the University of California, Irvine, and colleagues combined 40 years of satellite imagery and climate modeling. The models were used to estimate annual snowfall, which over time adds ice to the region’s glaciers. Then, the team measured the speed of ice flowing out to sea by tracking visual landmarks on the glaciers through time. This allowed them to estimate how much ice each of the continent’s many glaciers sent out to sea each year from 1979 to 2017. By subtracting the amount of ice added annually by snow from the amount of ice lost to sea, the researchers determined how much ice was gained or lost.

“After staring at satellite photos for hours you go a little cross-eyed, but it’s basic statistics—you beat down the noise by adding more data points,” Rignot says. “Tracking down these old satellite photos and spending months analyzing by hand was worth it to create this long-term record.”

Overall, the study found that Antarctica now sends six times more ice plunging into the sea each year than it did in 1979. During the 40-year period of the study, Antarctica added 13.8 millimeters to sea level, with the majority coming from West Antarctica. But East Antarctica, particularly the area known as Wilkes Land, was responsible for more than 30% of Antarctica’s contribution to sea level rise, the researchers report today in the Proceedings of the National Academy of Sciences. “The more we look at this system the more we realize this is a fragile system,” Rignot says. “Once these glaciers are destabilized there is no red button to press to stop it.”

If intensifying polar winds are responsible for the intrusion of warm waters beneath East Antarctica, the situation is likely to get worse, Rignot says. The increasing strength of those winds is owed in part to the contrast in temperature between Antarctica and the rest of the world. As greenhouse gases warm much of the planet, this temperature differential is likely to intensify, driving even stronger westerlies, he adds.

But the bold new results won’t be accepted without a fight, says glaciologist Richard Alley of Pennsylvania State University in University Park, who was not involved in either study. “There will be a lot of

AGS January 2019 Page 19

East Antarctica’s Ice is Melting at an Unexpectedly Rapid Clip, New Study Suggests (Continued) comparisons between the methods used to create these estimates and those in the [previous study],” he says. In addition to the ice-tracking method used in the current paper, the previous one also gathered two other measurements: one that estimated ice loss by repeatedly “weighing” the ice sheet via satellite, and one that estimated changes in elevation on the glacier’s surface from planes and satellites.

No matter the outcome, Rignot hopes the study brings greater attention to a part of Antarctica that has traditionally been understudied. Helen Fricker, a glaciologist at the Scripps Institution of Oceanography in San Diego, California, agrees. “We need to monitor the entirety of Antarctica and we just can’t do that without international cooperation,” Fricker says. “We can’t take our eyes off this ice.”

Read more about this article at: http://www.sciencemag.org/news/2019/01/east-antarctica-s-ice-melting-unexpectedly-rapid-clip-new-study- suggests Lessons From a Postdoc Gone Wrong I sat hunched over my computer screen, analyzing data, when a university administrator walked into our lab and handed out a series of sealed envelopes. Puzzled, I opened the letter addressed to me: “It has become necessary for the University to effect a layoff of your position as a Postdoctoral Scholar.” In silence, my labmates opened their own letters, all of which said essentially the same thing. I knew that our lab was under investigation, but I had no inkling that my job was in jeopardy, so the news came as a huge shock. My mind raced from concerns about my personal finances—“How will I pay rent?”—to questions about my future in science: “How will we finish our experiments? Will this mark the end of my research career?”

Three years earlier, I had started my postdoc brimming with enthusiasm, excited to work for a brilliant scientist on a project that, we hoped, would help people with hearing loss—a group that includes me. My enthusiasm was short-lived. Almost as soon as I arrived, it became clear that the lab had problems. For one, my supervisor had been receiving animal care violation warnings for the lab's work with mice for years. They continued to pile up during my tenure, at times forcing us to suspend our experiments. Eventually, our funding was cut off entirely and the lab was shut down.

I ended up digging out of the mess and moving on to a second postdoc. Now I'm back to doing research that I love in a functional lab, and I'm glad I persevered. But looking back, I wish I hadn't sunk so much time into my first postdoc lab. I should have quit and moved on much sooner. For others who may be in similar situations, here are tips to avoid drowning with a sinking ship.

DO NOT BE BLINDED BY PASSION. Enthusiasm and drive are key ingredients for scientific careers. However, they can be problematic when they prevent you from seeing warning signs clearly. My intense desire to find treatments to reverse hearing loss led me to mistakenly write off serious lab issues as small bumps in the road. Had I been more objective, I would have realized that those “bumps” were actually major obstacles.

TAKE PERSONNEL DYNAMICS SERIOUSLY. Collaboration and teamwork are essential in science; you can't function as an island. Blinded by passion, I disregarded the lack of honest communication with my supervisor about the problems in our lab. In retrospect, that was an obvious warning sign. DO NOT BE TRAPPED BY FEAR. I fretted that if I didn't publish anything from my postdoc, no one

Page 20 AGS January 2019

Lessons From a Postdoc Gone Wrong (Continued) would hire me. That's one reason I stuck with my ill-fated lab. But the concern turned out to be unfounded. Finding a new position after I was laid off wasn't easy, but I survived by being transparent about what happened and pushing forward with confidence. One thing that helped me move past my postdoc mess was looking back at my past successes to remind myself that I am a good scientist.

FOCUS ON YOURSELF. Pointing fingers is easy, but burning bridges—and wasting energy on casting blame—won't help you move forward. When problems arise, don't engage in pointless battles. Instead, take stock of your situation and decide what's best for you. Write down the pros and cons of your job; examine your career goals; and talk to your trusted mentors, colleagues, friends, and family. Along the way, be open to the possibility that it may be best to quit.

DO NOT WAIT FOR THE LAST STRIKE. Don't waste time in a bad environment. During my 3 years in my first postdoc lab, there were many times when I should have quit, but instead I hung on, hoping the situation would improve. Your life is not a game. Don't wait for strike three.

Read more about this article at: http://science.sciencemag.org/content/363/6424/314

AGS January 2019 Page 21

Fernbank Events & Activities

Pirate Day Fernbank After Dark: Love on the Brain Saturday, January 26, 2019 Friday, February 8, 2019

Come aboard for a day of pirate- Explore the science behind love and themed family fun. attraction through hands-on activities.

Learn more Learn more

Pterosaurs Opening Day Celebration Latin Dance Night Saturday, February 9, 2019 Friday, February 22, 2019

Take advantage of hands-on activities Enjoy and evening of Latin dancing for celebrating the new exhibit, Pterosaurs: ages 21+ only. Flight in the Age of the Dinosaurs. Learn more Learn more

Page 22 AGS January 2019

A New Way to Museum Take a walk on the wild side as you explore 75 acres of new outdoor nature adventures. WildWoods and Fernbank Forest combine to highlight the natural world through immersive trails, educational programming, hands-on exhibits and beautiful scenery.

You’ll discover something new each time you visit. You don’t have to drive north to enjoy the fall colors. Fernbank Forest and WildWoods come alive with dramatic yellows and oranges as the leaves change.

Nature Gallery Wild Huts and Hollows

The Nature Gallery is an outdoor exhibit space located in WildWoods. Permanent features include macro- sculptures representing the reproductive cycle of a sweetgum tree and giant photo frames that allow visitors to highlight nature’s beauty. This unique space also features rotating nature-inspired special exhibits throughout the year.

AGS January 2019 Page 23

Fernbank Museum of Natural History

(All programs require reservations, including free programs)

Now showing in the Fernbank IMAX movie theater:

Flying Monsters 3D Showing January 11 through June 1, 2019 Just as dinosaurs began their domination of Earth, pterosaurs ruled the prehistoric skies. Some with wingspans as long as a modern jet plane, these flying reptiles were as spectacular in appearance as they were amazing in flight. Join world-renowned naturalist and documentary filmmaker David Attenborough as he recounts the fascinating story of how we humans first discovered that these creatures were real and how they were even able to get off the ground and indeed soar...until their sudden disappearance from Earth. Great Barrier Reef 3D Showing December 14 through May 2, 2019 Every year millions of visitors travel by way of fins, flippers and feet to see one of the seven wonders of the natural world. So grab your mask and snorkel and come on an unforgettable adventure to the Great Barrier Reef. Narrated by acclaimed Australian actor Eric Bana, Great Barrier Reef 3D captures the natural beauty and exquisite strangeness of the world’s largest living wonder and introduces us to the visionaries and citizen scientists who are helping us better understand and protect this awesome, bizarre, and vibrant living world. Meet reef native Jemma Craig on an expedition to document efforts to preserve the reef and swim with giant mantas, sea turtles, sharks and Minke whales as you explore this awe- inspiring natural wonderland on the world’s largest screens!

Page 24 AGS January 2019

AGS Officers AGS Committees

President: Ben Bentkowski AGS Publications: Open [email protected] Phone (770) 296‐2529 Career Networking/Advertising: Todd Roach Phone (770) 242‐9040, Fax (770) 242‐8388

Vice‐President: Steven Stokowski [email protected]

[email protected] Continuing Education: Open

Secretary: Rob White Fernbank Liaison: Kaden Borseth Phone (770) 891‐0519 Phone (404) 929‐6342 [email protected] [email protected]

Treasurer: John Salvino, P.G. Field Trips: Open

Phone: 678‐237‐7329 Georgia PG Registration: Ken Simonton [email protected] Phone: 404‐825‐3439 Past President [email protected] Shannon Star George Ginny Mauldin‐Kenney,

[email protected] ginny.mauldin@gmailcom

Teacher Grants: Bill Waggener Phone (404)354‐8752 2019 Meeting Dates [email protected]

Listed below are the planned meeting Hospitality: John Salvino, P.G. dates for 2019. Please mark your calendar [email protected] and make plans to attend.

Membership Burton Dixon 2019 AGS Meeting Schedule [email protected] February 26

March 26 Social Media Coordinator: Carina O’Bara April 30 [email protected] May 28

June 25 Newsletter Editor James Ferreira 2019 PG Study Group Meetings Phone 508‐878‐0980

February 23 [email protected]

March 30 Web Master: Ken Simonton April 27 [email protected] May 25 June 29 www.atlantageologicalsociety.org

AGS January 2019 Page 25 ATLANTA GEOLOGICAL SOCIETY www.atlantageologicalsociety.org

ANNUAL MEMBERSHIP FORM Please print the required details and check the appropriate membership box.

DATE:______

NAME:______

ORGANIZATION:______

TELEPHONE (1): TELEPHONE (2):

EMAIL (1): EMAIL (2):

STUDENT $10

PROFESSIONAL MEMBERSHIP $25

CORPORATE MEMBERSHIP $100 (Includes 4 professional members, please list names and emails below)

NAME: EMAIL:

NAME: EMAIL:

NAME: EMAIL:

NAME: EMAIL:

For further details, contact the AGS Treasurer: John Salvino [email protected]

Please make checks payable to the “Atlanta Geological Society” and bring them to the next meeting or remit with the completed form to: Atlanta Geological Society, Attn: John Salvino 3073 Lexington Avenue Woodstock, Georgia 30189

To pay electronically; click https://squareup.com/store/atlanta‐geological‐society

CASH CHECK (CHECK NUMBER:______)