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Home , Glacial erratic, Glacial period, Last glacial period

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Bangor Daily News, Thursday, January 12, 2006, OUR CHANGING WORLD 3

Natural world keeps detailed records of its ecological past The history of is literally beneath “There are quite a few parts of the world tists important clues about the ancient atmos- “The deep ocean just receives . It our feet. Rocks alongside the road tell tales of that don’t have thick ice sheets to sample,” phere. Pollen grains, which have a surface par- just goes to the bottom [and stays there]. and ancient life, and marine clay soils Jacobson said. ticularly resistant to decay, can tell researchers There’s no ,” said Harold “Hal” Borns, in flower beds as far north as Millinocket Some Maine lakes have offered sediment which trees and plants lived in the region over a professor emeritus at the University of paint a picture of oceans stretching far inland. cores that reach as far back as 17,000 , time. Radiocarbon dating of organic matter in Maine and the founder of the Change But to understand the past, paleoecologists though 10,000- to 12,000- cores are far more the sample can link the findings to a precise Institute. — those who study the history of ’s common, particularly in bogs, many of which point in time. Elsewhere in the world, scientists also study plant and animal communities — dig much didn’t develop until several thousand years But the organisms that allow sediment sam- tree rings and the similar annual development deeper. after the ice completed its retreat. Others offer ples to be carbon dated also can mar the data. patterns of ocean corals and cave growths The beneath lakes and bogs have just a blink in geologic time. A burrowing insect or shellfish disturbs just a such as stalactites to understand a shifting cli- quietly been transcribing a changing world “You may find that the lake just formed few inches of lake bottom, but those inches mate. A wider ring could mean a milder sea- since they were formed with the retreat of the 1,000 years ago, and you’re out of luck,” said might represent 50 years of history, which son or an increase in precipitation, while a glaciers from Maine at least 12,000 years ago. Ron Davis, a professor emeritus at the univer- become blended together, Davis explained. slight change in the chemical makeup of coral Every year, pollen and leaves fall from the sity and one of the founding members of the Some of these less precise records remain can reveal a great deal about the ancient ocean trees and slowly drift to lake bottoms or cling Climate Change Institute. useful, as proof of sweeping climatic change. and atmosphere. to sphagnum moss. Perhaps 60 cores that extend all the way Other, less common cores, from lakes where One biological record by itself means very “It’s like having a recorder, running from back to the retreat of the glaciers have been fewer insects or shellfish existed, can be near- little, but when hundreds of samples all show the day the lake is formed,” said George Jacob- taken in Maine and fully examined by biolo- ly as precise as ice cores, offering a year-by- the same trends, scientists can begin to piece son, a paleoecologist at the Climate Change gists. Many more samples are in storage await- year history of the region, Davis said. together a mosaic of ancient landscapes, Institute at the University of Maine. ing someone with the time and funds to under- The only sediment records than can begin Jacobson said. In places like Maine, where glaciers no take the six solid months of research it can to challenge ice for sheer longevity are the “It’s really a tremendous natural history,” longer exist, biological records often provide require to analyze a sample, Davis said. cores of ocean sediment that can contain hun- he said. “It allows us to piece the whole story the best view into the ecological past. Tests of the soil chemistry can give scien- dreds of thousands of years of history. together in a way that’s pretty incredible.” Trail will follow glaciers’ legacy in the landscape of coastal Maine

Today, blueberry bushes drenched Maine, covering every inch of its Borns is creating an , expand the trail to the entire state of cross County. in the greens of spring or aflame land and weighing down the surface a journey across coastal Maine with Maine. offers tourists the with the colors of autumn blanket so much so that when the ice rapidly glacial clues as its signposts. The “There are spectacular examples National Ice Age Trail, while Wash- the ridges of Maine’s Down East melted, seawater flooded in, follow- trail winds through Hancock and of just about everything … , ington is considering a trail to edu- region. ing the Penobscot River as far Washington counties highlighting , deltas, erratics [through- cate people about the glacial origins But somewhere between 23,000 north and east as Millinocket. some of the most accessible features out the state],” said Woodrow of the Cascades region. Borns and and 28,000 years ago, when a mile- In Maine, the signs of glaciation that were sculpted into the landscape Thompson, a geologist with the his colleagues have spent decades deep mountain of ice was beginning are all around, from Acadia’s famed by tons of moving ice. The trail Maine Geological Survey. mapping glacial footprints on the long, slow retreat that would Bubble — an orphan boulder includes Cadillac Mountain — the Climate change doesn’t just affect Maine’s landscape. “So why not a mark the end of a in known as a “” that was first land to emerge from the ice as it the and it doesn’t just trail here?” he asked himself. Maine, the frigid coast was no Vaca- dropped by the ice as it passed over made its final retreat — and contin- change the habitat for plants and ani- “We’ve got all the science done. All tionland. South Bubble Mountain — to the ues east across the land where gla- mals. When mountains of ice scrape we’ve got to do is put it together in a The very hills that give blueberry Great Basin of Mount Katahdin ciers once met the sea. Between across Earth, climate change has the map,” Borns said. country its well-drained, sandy soil itself, shaped by the glaciers that 12,000 and 17,000 years ago, the gla- power to alter the very landscape. With federal funding, Borns has were once glacial moraines — moat- once nestled into its valleys. ciers were gone from Maine, but Borns likes to use a three-dimen- been working on the project for sev- like deposits of sand and gravel that Harold “Hal” Borns, founder of their footprints remain. sional map of Maine’s landscape to eral years and he hopes to make formed as water rushed from the the University of Maine’s Climate For tens of thousands of years, ice explain the recession of glaciers available by this spring a printed melting . Change Institute, has spent his life was on the move, seasonally advanc- across the state over thousands of map of a driving route between gla- Sediment samples and other data studying the geological signals of ing and retreating as it slowly reced- years. cial features along the coast. He reveal that Maine’s climate at the glaciers and is amazed at how little ed, all the while scraping bedrock, “There’s a climate change right already shares considerable informa- time probably resembled far north- people know about the catastrophic dropping boulders and hollowing out there,” Borns said, pointing to a long tion about some of the locations in ern or portions of climate shift that shaped their state. lakes. The first Ice Age Trail map ridge near Addison that clearly an interactive map online at: that are today within the Arctic Cir- “[Mainers] live and die on this will focus on the moraines of coastal shows one of the moraines that criss- http://iceagetrail.umaine.edu. cle. landscape, and most of it is glacial,” Maine, where the made its Glaciers shaped the state of he said. last stand. Borns hopes eventually to Glacial melt and land rebound As glaciers receded, previously depressed land rebounded, released from the weight of the ice load. ’s last ice sheet Maine La ssive retreat of the urentide Continental I 17,5 Maine and the progre 0 ce Sheet 00 years ago The Ice Age in Maine e last ice sheet, 17,50 1.5 to 2 miles high southern edge of th Land surface ago. to 12,000 years 17,500 years ago Present Vast ice sheets (similar to the ones with the in 12.9 land surface 17,500 Greenville years ago that now cover Greenland and experience peaking about 20,000 Bangor The glacier Maine coast ) once blanketed a signi- years ago, with most of the ice margin stood Bedrock .8 ficant portion of the North American melting during the period 17,500- in the Bangor 13 12.9 area about Laurentid continent. During the last million 12,500 years ago. Much of what we 15,600 e Continental Ice Sheet 15,500 years ago Pre years ago. sent years, roughly the time during which call human , therefore, land Land surface surfa Se have existed as a species, including the practice of agriculture, 15,500 years ago ce a level 15,500 years ago (higher than at present) Earth experienced about a dozen emerged only during the most recent 15.1 Greenville .3 glaciations. During the greatest of period. 13 Bangor Maine coast them, about 650,000 years ago, the During the last million years or so Bangor 15.6 Laurentide Continental Ice She Laurentide Continental Ice Sheet, (the ), glacial et/Maine 12,500 years ag 15.1 Prese o with its northernmost reaches up periods have come at fairly regular nt lan .9 d sur 15.6 15 face Sea level 12,500 year near Hudson Bay, covered Chicago intervals of about 100,000 years. This Greenville s ago (lower than at present) and points south in ice perhaps a mile periodicity is partly explained by the 15.9 The timeline Land surface Bangor re measured in 12,500 years ago Maine thick. So much water was bound up “Milankovitch hypothesis,” which 17.2 figures a Rebound coast thousands of years in in ice that the level of the seas was states that regular wobbles and tilts the past. Greenville about 400 feet lower than it is in Earth’s axis of spin, as well as Present currently. stretches in its orbit, cause changes Pres Bangor Maine After glacial ice receded, ent la nd su coast Present sea level Glacial periods tended to last much in how warm the planet is, especially the depressed ground slowly rface rebounded, released from its longer than the interglacial periods, in the . Co load of ice. ntine s ntal helf

Sea was in Much of Glacier had contact with southern Maine disappeared ice margin. was ice-free. and sea had Sea covered retreated coastal from coastal lowland. Maine. 17,500 15,500 12,500 years years years Maine Ice Cap ago ago ago

Laurentide Continental Laurentide Continental Ice Sheet Ice Sheet

Continental Laurentide Continental shelf Continental Ice Sheet shelf Till Till Continental shelf Bedrock Bedrock Bedrock

Moraine Moraine Marine clay Marine clay Marine clay

1. Thick Laurentide Continental 1. Ice front retreats to station- 1. A small isolated segment of Ice Sheet advances out onto ary position just north of pres- ice is present in northern the Continental Shelf into the ent-day Bangor. Maine. Gulf of Maine 2. Land surface/crust remains 2. Released from the weight of 2. Weight of the ice depresses mostly depressed, but release the ice, land surface/crust land surface downward. of ice’s weight causes crust rebounds and emerges up and 3. Relative sea level at ice to begin to rebound. out of the ocean. front is about 300 feet higher 3. In contact with the retreat- 3. Relative sea level drops to a than present-day sea level. ing ice margin, sea level is at low-stand well off the present Maximum extent of the Extent of the Laurentide about 400 feet above present- Extent of the Laurentide coast to about 200 feet below Laurentide Continental Ice Sheet Continental Ice Sheet on day sea level. Continental Ice Sheet on the present-day sea level. on North America North America Present-Day Profile 1. Laurentide Continental Ice Sheet has melted and disappeared from North America. The Greenland Ice Cap is the only remnant of last ice age. 2. The land surface-crust has rebounded and been restored to its present-day level. 3. Sea level rose once again to its present position at the coast due to the infilling of the ocean by the meltwater from the collapse of the Laurentide Continental Ice Sheet in North America, and the Scandinavian Ice Sheet in .

65 million years ago 5.8 million to 2 million to 100,000 years ago The end of the era of the dinosaurs. Today, many scientists 5.2 million years ago 1.6 million years ago The first modern support the theory that a massive asteroid struck Earth, fill- Man's earliest-known The beginning of the Period, in which Earth's humans, Homo ing the atmosphere with dust and debris for several years ancestor, Ardipithecus climate continues to cool, introducing a long glacial cycle sapiens, appear in and causing a drastic but temporary climate change that ramidus kadabba, that lasts to the present. Glaciers have advanced into Africa. few species could survive. appears in Africa. temperate zones at least nine times, each occurrence bringing at least 90,000 years of ice buildup, followed by rapid melting and around 10,000 years of relief known as an “interglacial” period. Geologic evidence of at least two of these glaciations exists in New .