India Time after time N. China Continents break Australia S. China Siberia apart and rejoin over hundreds of millions of years, S. China resculpting Earth’s Australia ever-changing face. Laurentia N. China Siberia Congo/São Francisco Kalahari Laurentia Baltica Congo/São W. Africa Francisco Amazonia Baltica Amazonia W. Africa Nuna Rodinia 1.4 billion years ago 750 million years ago New studies of magnetic minerals in rock from SUPERCONTINENT Brazil, for instance, are helping pin the ancient Amazon to a spot it once occupied in Nuna’s heart. Other recent research reveals the geo­ SUPERPUZZLE logic stresses that finally pulled Rodinia apart, some 750 million years ago. Scientists have even Geologists trace the comings and goings predicted when and where the next superconti­ nent may form — an amalgam of North America of Earth’s landmasses By Alexandra Witze and Asia, evocatively named Amasia — some 250 million years from now. Look at any map of the Atlantic Ocean, and you Reconstructing supercontinents is like trying might feel the urge to slide South America and to assemble a 1,000­piece jigsaw puzzle after you’ve Africa together. The two continents just beg to lost a bunch of the pieces and your dog has chewed nestle next to each other, with Brazil’s bulge up others. Still, by figuring out which puzzle pieces locking into West Africa’s dimple. That visible went where, geologists have been able to illumi­ clue, along with several others, prompted Alfred nate some of Earth science’s most fundamental Wegener to propose over a century ago that questions. the continents had once been joined in a single For one thing, continental drift, that grad­ enormous landmass. He called it Pangaea, or ual movement of landmasses across Earth’s “all lands.” surface, profoundly affected life by allowing spe­ Today, geologists know that Pangaea was just cies to move into different parts of the world the most recent in a series of mighty super­ depending on what particular landmasses hap­ continents. Over hundreds of millions of years, pened to be joined. (The global distribution of enormous plates of Earth’s crust have drifted dinosaur fossils is dictated by how continents together and then apart. Pangaea ruled from were assembled when those great animals about 400 million to 200 million years ago. But roamed.) R. MITCHELL EVANS; 2016; D.A.D. wind the clock further back, and other superconti­ Supercontinents can also help geologists hunt­ nents emerge. Between 1.3 billion and 750 million ing for mineral deposits — imagine discovering years ago, all the continents amassed in a great gold ore of a certain age in the Amazon and using it land known as Rodinia. Go back even further, to find another gold deposit in a distant landmass MURPHY (EDS.)/ LI AND J.B. Z.-X. EVANS, D.A.D. SOURCES: about 1.4 billion years or more, and the crustal that was once joined to the Amazon. More broadly, shards had arranged themselves into a supercon­ shifting landmasses have reshaped the face of the tinent called Nuna. planet — as they form, supercontinents push up Using powerful computer programs and geologic mountains like the Appalachians, and as they clues from rocks around the world, researchers break apart, they create oceans like the Atlantic. are painting a picture of these long­lost worlds. “The assembly and breakup of these continents FULLER; NICOLLE RAGER ART: HISTORY EARTH THROUGH CYCLES SUPERCONTINENT 18 SCIENCE NEWS | January 21, 2017 Siberia Baltica N. America N. China China 2.1 billion years ago: Laurentia Landmasses begin Siberia assembling toward S. America the first true known supercontinent, Australia Nuna (also known as Columbia). W. Africa S. China Antarctica 1.5 billion years ago: Nuna reaches its Amazonia maximum landmass. Congo/São Francisco Australia 1.3 billion years ago: India Nuna begins to fragment and the parts reassemble as Rodinia. Pangaea Amasia 200 million years ago 250 million years from now 1 billion years ago: Rodinia reaches have profoundly influenced the evolution of the the Pacific Ocean is shrinking, its seafloor sucked maximum landmass. whole Earth,” says Johanna Salminen, a geophysi­ down by subduction along the Ring of Fire — loop­ cist at the University of Helsinki in Finland. ing from New Zealand to Japan, Alaska and Chile. 750 million years ago: By running the process backward in time, geol­ Rodinia begins to Push or pull ogists can begin to see how oceans and continents break apart, creating the Pacific Ocean. For centuries, geologists, biogeographers and have jockeyed for position over millions of years. explorers have tried to explain various features Computers calculate how plate positions shifted of the natural world by invoking lost continents. over time, based on the movements of today’s 400 million years ago: Subducting ocean Some of the wilder concepts included Lemuria, a plates as well as geologic data that hint at their crust once again sunken realm between Madagascar and India that past locations. shifts landmasses offered an out­there rationale for the presence of Those geologic clues — such as magnetic min­ toward one another, in early steps toward lemurs and lemurlike fossils in both places, and erals in ancient rocks — are few and far between. Pangaea. Mu, an underwater land supposedly described in But enough remain for researchers to start to ancient Mayan manuscripts. While those fantas­ cobble together the story of which crustal piece 300 million years ago: tic notions have fallen out of favor, scientists are went where. Pangaea reaches exploring the equally mind­bending story of the “To solve a jigsaw puzzle, you don’t necessar­ maximum landmass. supercontinents that actually existed. ily need 100 percent of the pieces before you Earth’s constantly shifting jigsaw puzzle of con­ can look at it and say it’s the Mona Lisa,” says 200 million years ago: tinents and oceans traces back to the fundamental Brendan Murphy, a geophysicist at St. Francis Pangaea begins to forces of plate tectonics. The story begins in the Xavier University in Antigonish, Nova Scotia. break apart, creating the Atlantic Ocean. centers of oceans, where hot molten rock wells “But you need some key pieces.” He adds: “With up from deep inside the Earth along underwater the eyes and nose, you have a chance.” mountain chains. The lava cools and solidifies into Next big event: About 250 million newborn ocean crust, which moves continually No place like Nuna years from now: away from either side of the mountain ridge as if For ancient Nuna, scientists are starting to find North America and carried outward on a conveyor belt. Eventually, the first of those key pieces. They may not reveal Asia will smash together with other the moving ocean crust bumps into a continent, the Mona Lisa’s enigmatic smile, but they are at land fragments to where it either stalls or begins diving beneath that least starting to fill in a portrait of a long­vanished create the supercon- continental crust in a process called subduction. supercontinent. tinent Amasia. Those competing forces — pushing newborn Nuna came together starting around 2 billion SOURCES: D. EVANS; J. MEERT; Z.-X. LI, D.A.D. EVANS, J.B. MURPHY/ crust away from the mid­ocean mountains years ago, with its heart a mash­up of Baltica SUPERCONTINENT CYCLES THROUGH and pulling older crust down through subduc­ (the landmass that today contains Scandinavia), EARTH HISTORY 2016; M. YOSHIDA/ GEOLOGY 2016 tion — are constantly rearranging Earth’s crustal Laurentia (which is now much of North America) plates. That’s why North America and Europe are and Siberia. Geologists argue over many things getting farther away from each other by a few cen­ involving this first supercontinent, starting with timeters each year as the Atlantic widens, and why its name. “Nuna” is from the Inuktitut language of www.sciencenews.org | January 21, 2017 19 FEATURE | SUPERCONTINENT SUPERPUZZLE the Arctic. It means lands bordering the northern we can say Congo could have been there.” Like oceans, so dubbed for the supercontinent’s Arctic­ building out a jigsaw puzzle from its center, the fringing components. But some researchers prefer work essentially expands Nuna’s core. to call it Columbia after the Columbia region of North America’s Pacific Northwest. Rodinia’s radioactive decay Whatever its moniker, Nuna/Columbia is an By around 1.3 billion years ago, Nuna was breaking exercise in trying to get all the puzzle pieces to apart, the pieces of the Mona Lisa face shattering fit. Because Nuna existed so long ago, subduction and drifting away from each other. It took another has recycled many rocks of that age back into the 200 million years before they rejoined in the con­ deep Earth, erasing any record of what they were figuration known as Rodinia. doing at the time. Geologists travel to rocks that Recent research suggests that Rodinia may not remain in places like India, South America and have looked much different than Nuna, though. “As soon as you North China, analyzing them for clues to where The Mona Lisa in its second incarnation may still they were at the time of Nuna. have looked like the portrait of a woman — just start asking One of the most promising techniques targets maybe with a set of earrings dangling from her why [Pangaea] magnetic minerals. Paleomagnetic studies use the lobes. formed, how minerals as tiny, time capsule compasses, which A team led by geologist Richard Ernst of Carleton it formed and recorded the direction of the magnetic field at the University in Ottawa, Canada, recently explored time the rocks formed. The minerals can reveal the relative positions of Laurentia and Siberia what processes information about where those rocks used to between 1.9 billion and 720 million years ago, a are involved ..