[_ Old Earth _] A History of Life on Earth

[M82A1]

Tertiary Volcanics:

Volcanic activity was extensive during the Tertiary. Flood basalts were caused by hot spot volcanism, with plumes of magma rising to the surface from deep within the mantle. India's Deccen Traps are perhaps the greatest outpouring of basalt on land during the last 250 million years. About 65 million years ago, a giant rift ran down the west side of India, and huge volumes of molten magma poured onto the surface. Some 100 separate flows spilled over 350,000 cubic miles of lava onto much of west-central India, totaling up to 8,000 feet thick over a period of several million years. If spread evenly, that vast amount of lava would envelop the entire world in a layer of volcanic rock some 10 feet thick.

During the eruptions, India was about 300 miles northeast of Madagascar, as it continued drifting toward southern Asia. The Seychelles Bank is a large oceanic volcanic plateau that became separated from the Indian subcontinent and is now exposed on the surface of several islands. The massive outpourings of carbon dioxide-laden lava might have created the extraordinary warm climate of the Paleocene that sparked the evolution of the mammals.

Continental rifting that occurred at approximately the same time as the Deccen Traps eruptions began separating Greenland from Norway and North America. The rifting poured out great flood basalts across eastern Greenland, northwestern Britain, northern Ireland, and the Faeroe Islands, between Britain and Iceland. The island of ice is itself an expression of the Mid-Atlantic Ridge, where massive floods of basalt formed a huge volcanic plateau that rose above sea level about 16 million years ago.

Evidence of substantial explosive volcanism lies in an extensive region from the South Atlantic to Antarctica. The Kerguelen plateau located north of Antarctica is the world's largest submerged volcanic plateau. It originated from the ocean floor more than 90 million years ago, when a series of volcanic eruptions released immense quantities of basalt onto the Antarctic plate. The timing also coincides with a mass extinction of species. The Ninety East Ridge, named for its longitude, 90 degrees east, is an undersea volcanic mountain range that runs 3,000 miles south from the Bay of Bengal, India, and formed when the Indian plate passed over a hot spot as it continued drifting toward Asia.

Prior to the opening of the Red Sea and Gulf of Aden, massive floods of basalt covered some 300,000 square miles of Ethiopia, beginning about 35 million years ago. The East African Rift Valley extends from the shores of Mozambique to the Red Sea, where it splits to form the Afar Triangle in Ethiopia. For the past 25 to 30 million years, the Afar Triangle has been stewing with volcanism. An expanding mass of molten magma lying just beneath the crust uplifted much of the area thousands of feet.

In North America, major episodes of basalt volcanism occurred in the Columbia River Plateau, the Colorado Plateau, and the Sierra Madre region in northern Mexico. A band of volcanoes stretching from Colorado to Nevada produced a series of very violent eruptions between 30 million and 26 million years ago. Beginning about 17 million years ago and extending over a period of 2 million years, great outpourings of basalt covered Washington, Oregon, and Idaho, creating the Columbia River Plateau. Massive floods of lava enveloped an area of about 200,000 square miles, in places reaching 10,000 feet thick. Periodically, volcanic eruptions spewed out batches of basalt as large as 1,200 cubic miles, forming lava lakes up to 450 miles wide in a matter of days.

The volcanic episodes might be related to the present Yellowstone hot spot, which was beneath the Columbia River Plateau region. The hot spot moved eastward relative to the North American plate and can be traced by following volcanic rocks for 400 miles across Idaho's Snake River Plain. During the last 2 million years, it was responsible for three major episodes of volcanic activity in the vicinity of Yellowstone National Park, Wyoming, which number among the greatest catastrophes of nature.

 

[M82A1]

Cenozoic Mountain Building:

The Cenozoic is known for its intense mountain building, and the spurt in mountain growth over the past 5 million years might have triggered the Pleistocene ice ages. The Rocky Mountains, extending from Mexico to Canada, heaved upward during the Laramide orogeny from about 80 million to 40 million years ago. During the Miocene epoch, beginning some 25 million years ago, a large portion of western North America uplifted, and the entire Rocky Mountain region rose about a mile above sea level. Great blocks of granite soared high above the surrounding terrain, while to the west in the Basin and Range Province the crust stretched and in some places dropped below sea level.

Arizona's Grand Canyon is at the southwest end of the Colorado plateau, a generally mounain-free expanse that stretches from Arizona north into Utah and east into Colorado and New Mexico. Initially, the area surrounding the canyon was almost totally flat. Over the last 2 billion years, heat and pressure buckled the land into mountains that were later flattened by erosion. Again, mountains formed and eroded, and the region flooded with shallow seas. The land was uplifted another time with the rising of the Rocky Mountains. Between 10 and 20 million years ago, the Colorado River began eroding layers of sediment, exposing the raw basement rock below, and its present course is less than 6 million years old.

About 30 million years ago, the North American continent approached the East Pacific Rise, the counterpart of the Mid-Atlantic Ridge. The first portion of the continent to override the axis of seafloor spreading was the coast of southern California and northwest Mexico. When the rift system and subduction zone converged, the intervening oceanic plate dove into a deep trench. The sediments in the trench were compressed and thrust upward to form California's Coast Ranges. A system of faults associated with the 650-mile-long San Andreas Fault crisscrosses the mountain belt. The Sierra Nevada Range to the east, which rose about 7,000 feet over the last 10 million years, might be buoyed by a mass of hot rock in the upper mantle.

In the Pacific Northwest of the United States and British Columbia, the Juan de Fuca plate dove into a subduction zone located beneath the continent. As the 50-mile-thick crustal plate subducted into the mantle, its heat melted parts of the descending plate and the adjacent lithospheric plate, forming pockets of magma. The magma rose toward the surface, forming the volcanoes of the Cascade Rang, which erupted one after another.

India and the rocks that comprise the Himalayas broke away from Gondwana early in the Cretaceous, sped across the ancestral Indian Ocean, and slammed into southern Asia about 45 million years ago. As the Indian and Asian plates collided, the oceanic lithosphere between them thrust under Tibet, destroying 6,000 miles of subduction plate. The increased buoyancy uplifted the Himalayan Mountains and the broad Tibetan Plateau, the equal of which has probably not existed on this planet for over a billion years.

During the past 5 to 10 million years, the entire region rose over a mile in elevation. The continental collision heated vast amounts of carbonate rock, spewing several hundred trillion tons of carbon dioxide into the atmosphere, which might explain why the Earth grew so warm during the Eocene epoch from 54 million to 37 million years ago, when temperatures reached the highest of the past 65 million years. According to the fossil record, winters were warm enough for crocodiles to roam as far north as Wyoming, and forests of palms, cycads, and ferns covered Montana.

About 50 million years ago, the Tethys Sea separating Eurasia from Africa narrowed as the two continents approached each other, then began to close off entirely some 20 million years ago. Thick sediments that had been accumulating for tens of thousands of years buckled into long belts of mountain ranges on the northern and southern flanks. The contact between the continents initiated a major mountain building episode that raised the Alps and other ranges in Europe and squeezed out the Tethys Sea.

This episode of mountain building, called the Alpine orogeny, raised the Pyrenees on the boarder between Spain and France, the Atlas Mountains of northwest Africa, and the Carpathians in east-central Europe. The Alps of northern Italy formed in much the same manner as the Himalayas, when the Italian prong of the African plate thrust into the European plate.

In South America, the mountainous spine that comprises the Andes and runs along the western edge of the continent rose throughout much of the Cenozoic due to an increase in crustal buoyancy from the subduction of the Nazca plate beneath the South American plate. By the time all the continents had wandered to their present positions and all the mountain ranges had risen to their current heights, the world was ripe for the coming of the ice age.

 

[M82A1]

Tertiary Tectonics:

Changing climate patterns resulted from the movement of continents toward their present positions, and intense tectonic activity built landforms and raised most mountain ranges of the world. Except for a few land bridges exposed from time to time, plants and animals were prevented from migrating from one continent to the other. About 57 million years ago Greenland began to separate from North America and Eurasia. Prior to about 4 million years ago, Greenland was largely ice-free, but today the world's largest island is buried under a sheet of ice up to 2 miles thick. Alaska connected with east Siberia and closed off the Arctic Basin from warm water currents originating in the tropics, resulting in the formation of pack ice in the Arctic Ocean.

A narrow, curved land bridge that temporarily connected South America with Antarctica assisted in the migration of marsupials to Australia. Sediments containing fossils of a large crocodile, a 6-foot flightless bird, and a 30-foot whale suggest that land bridges existed as late as 40 million years ago. Antarctica and Australia then broke away from South America and moved eastward. When the two continents rifted apart, Antarctica moved toward the South Pole, while Australia continued in a northeastward direction. After Antarctica separated from Australia in the Eocene about 40 million years ago, it drifted over the South Pole, and acquired a permanent ice sheet that buried most of its terrain features.

The Mid-Atlantic Ridge system, which generates new ocean crust in the Atlantic Basin, began to occupy its present location midway between the Americas and Eurasia/Africa about 16 million years ago. Iceland is a broad volcanic plateau of the Mid-Atlantic Ridge that rose above sea level at about the same time. About 3 million years ago, the Panama Isthmus separating North and South America uplifted as oceanic plates collided. Prior to the continental collision, South America had been an island continent for the past 80 million years, during which time its mammals evolved undisturbed by outside competitors.

A barrier created by the land bridge isolated Atlantic and Pacific species, and extinctions impoverished the once rich fauna of the western Atlantic. The new landform halted the flow of cold water currents from the Atlantic into the Pacific, which along with the closing of the Arctic Ocean from warm Pacific currents might have initiated the Pleistocene glacial epoch. Never before have permanent ice caps existed at both poles, suggesting that the planet has been steadily cooling since the Cretaceous, when average global temperatures were 10 to 15 degrees Celsius warmer than today.

 

[M82A1]

Closing of the Tethys:

The Tethys Sea was a large, shallow equatorial body of water that separated the southern and northern continents during the Mesozoic and early Cenozoic. About 17 million years ago, the Tethys, which linked the Indian and Atlantic oceans, began to close off as Africa rammed into Eurasia. The collision also initiated a major mountain building episode that raised the Alps and other ranges. The climates of Europe and Asia were warmer and forests were widespread and lusher than today.

The Mediterranean Basin was apparently cut off from the Atlantic Ocean 6 million years ago, when an isthmus, created at Gibraltar by the northward movement of the African plate, formed a dam across the strait. Nearly a million cubic miles of seawater evaporated, almost completely emptying the basin over a period of about 1,000 years. The adjacent Black Sea, which is 750 miles long and 7,000 feet deep, might have had a similar fate. Like the Mediterranean, it is a remnant of an ancient equatorial sea that separated Africa from Europe.

The collision of the African plate with the Eurasia plate squeezed out the Tethys, resulting in a long chain of mountains and two major inland seas, the ancestral Mediterranean and a composite of the Black, Caspian, and Aral Seas, called the Paratethys, which covered much of Eastern Europe. About 15 million years ago, the Mediterranean separated from the Paratethys, which became a brackish (slightly salty) sea, much like the Black Sea of today.

The disintegration of the great inland waterway was closely associated with the sudden drying of the Mediterranean. The waters of the Black Sea drained into the desiccated basin of the Mediterranean. In a brief moment in geologic time, the Black Sea became practically a dry basin. Then during the last ice age, it refilled again and became a freshwater lake. The brackish and largely stagnant sea that occupies the basin today has evolved since the end of the last ice age.

 

[M82A1]

Chapter Fourteen:
Quaternary Glaciation:

The Quaternary period, from 3 million years ago to the present, witnessed a progression of ice ages that occurred almost like clockwork. The movement of continents to their present locations and the raising of land to higher elevations made geographic conditions ripe for a colder climate. Variations in the Earth's orbital motions might have provided the initial kick to trigger the growth of continental glaciers, which partly explains the recurrence of the ice age cycles about every 100,000 years. Once in place, the glaciers became self-sustaining by controlling the climate to their benefit. Then, mysteriously, in only a few thousand years, the great ice sheets collapsed and rapidly retreated to the poles.

Many northern lands owe their unusual topographies to massive ice sheets that swept down from the polar regions during the Pleistocene epoch of the last 3 million years. The invasion was so pervasive that ice sheets 2 miles or more thick enveloped upper North America and Eurasia, Antarctica, and parts of the Southern Hemisphere. In many areas, the glaciers stripped off entire layers of sediment down to the bare bedrock, erasing the entire geologic history of the region. The last ice age even destroyed evidence of earlier glaciations, as great ice sheets eradicated much of the northern landscape.


The Age of Man:

About 3 million years ago, huge volcanic eruptions in the northern Pacific Ocean darkened the skies and global temperatures plummeted, culminating in a series of glacial episodes. The climate change prompted a shift from forested environments to open savanna habitats in Africa. These changing conditions produced many new animal species and spurred the evolution of early humans. Indeed, we are products of the ice ages, which spanned the whole of human experience.

Our direct ancestors the hominids evolved in Africa, probably from the same species that gave rise to the great apes, including the gorilla and chimpanzee. Around 7 million years ago, much of Africa entered a period of cooler, drier climates when forests retreated and were replaced with grasslands. Life on the savanna, where our ancient ancestors roamed, was harsher and more challenging than life in the forests, where the apes lived. To survive under these difficult conditions, early humans rapidly evolved into intelligent, upright-walking species, whereas the apes are much the same today as they were millions of years ago.

An early hominid species called Australopithecus first appeared in Africa about 4 million years ago. It walked on two legs but retained many ape-like features, such as long arms in relation to its legs and curved bones in its hands and feet. The species was quite muscular and considerably stronger than modern humans. Males stood less than 5 feet tall and weighed about 100 pounds, and females stood about 4 feet tall and weighed about 70 pounds. Two or more lines of Australopithecene lived simultaneously in Africa and survived practically unchanged for more than a million years. After a lengthy period of apparent stability, all but one line became extinct, possibly due to a changing climate or habitat.

The most successful of the early hominids was Homo habilis, which evolved a little over 2 million years ago. It was a transitional species, somewhere between primitive ape-like hominids and humans. Its brain was about half the size of a modern human brain. The limb bones were markedly different from earlier hominids and more closely resembled those of later humans. It was the first human species to make and use tools and had a well-developed speech center, indicating a primitive language capability.

Homo habilis disappeared from Africa around 1.8 million years ago and was replaced by Homo erectus. This species is widely accepted as human and appears to have evolved in Africa directly from Homo habilis. It also could have evolved independently in Asia and subsequently migrated to Africa. About a million years ago, this early human occupied southern and eastern Asia, where it lived until about 200,000 years ago. Its advanced features suggest a spurt of evolutionary development, as it shares many attributes with modern humans. Its brain was also larger, about two-thirds the size of a modern human's.

Many types of Homo erectus then scattered throughout the world, which suggests that anatomically modern humans evolved from this species in several places, possibly accounting for the differences in races among people today. Peking man, a variety of Homo erectus that lived in China about 400,000 years ago, dwelling in caves and was possibly the first to use fire. Another variety, called Java man, arrived in Java about 700,000 years ago. About 60,000 years ago, the descendants of Java man migrated to Australia and possibly to the South Pacific islands.

The earliest Homo sapiens, called Cro-Magnon for the Cro-Magnon cave in France where the first discoveries were made in 1868, originated in Africa perhaps 200,000 years ago. Evidence also suggests they arose simultaneously in several parts of the world, as much as a million years ago, possibly evolving directly from Homo erectus. The Cro-Magnon shared most of the physical attributes of modern humans. The skull, whose brain case proportions were modern in structure, was short, high, and rounded, and the lower jaw ended in a definite chin. The rest of the skeleton was slender and long-limbed compared to earlier species of Homo.

Sometime during the last ice age, Cro-Magnon appears to have advanced into Europe and Asia during a warm interlude when the climate was less severe. They probably lived much like present-day natives of the Arctic tundra, fishing the rivers and hunting reindeer and other animals. Due to the scarcity of wood in the cold tundra, ice age hunters on the central Russian plain built houses of mammoth bones and tusks covered with animal hides and burned animal bones and animal fat for heat and light.

The Neanderthals were primitive Homo sapiens, named for the Neander Valley near Dusseldorf, Germany, where the first fossils were recognized in 1856. They are generally thought to have inhabited caves, but they also occupied open-air sites, as evidenced by hearths and rings made of mammoth bones and stone tools normally associated with these people. During the last interglacial period, called the Eemian, which ran from about 135,000 to 115,000 years ago, the Neanderthals ranged over most of western Europe and central Asia, extending far north as the Arctic Ocean.

Modern humans and Neanderthals apparently coexisted in Eurasia for at least 60,000 years and shared many cultural advancements. The Neanderthals thrived in these regions until about 30,000 years ago, declining over a period of perhaps 5,000 years. The disappearance of the Neanderthals might have resulted from their replacement or assimilation by modern humans.

 

[M82A1]

The Pleistocene Ice Ages:

From the end of the Permian 250 million years ago to about 40 million years ago, no major ice caps covered the world, suggesting that the existence of ice sheets at both poles during the Pleistocene was a unique event in Earth history. Analysis of deep-sea sediments and glacial ice cores provides a historical record of the recent ice ages, which began about 3 million years ago, when a progression of glaciers sprawled across the northern continents.

During this time, the surface waters of the ocean cooled dramatically, causing diatoms, a species of algae with shell made of silica, to sharply decline in the Antarctic, presumably when sea ice reached its maximum northern extent, thus shading the algae below. In the absence of sunlight for photosynthesis, the diatoms vanished, and their disappearance marks the initiation of the Pleistocene glacial epoch in the Northern Hemisphere.

The latest period of glaciation began over 100,000 years ago, intensified about 75,000 years ago, possibly due to the massive Mount Toba eruption in Indonesia, and peaked about 18,000 years ago. During the height of the last ice age, glaciers up to 2 or more miles thick enveloped Canada, Greenland, and Northern Europe.

In North America, the largest ice sheet, called the Laurentide, blanketed an area of 5 million square miles. It extended from Hudson Bay, reaching northward into the Arctic Ocean and southward into eastern Canada, New England, and the upper midwestern United States. A smaller ice sheet called the Cordilleran originated in the Canadian Rockies and engulfed western Canada, along with the northern and southern parts of Alaska, leaving an ice-free corridor down the middle, used by humans migrating into North America. Glaciers also covered small portions of the northwestern United States.

The largest ice sheet in Europe, the Fennoscandian, fanned out from northern Scandinavia and covered most of Great Britain as far south as London and large parts of northern Germany, Poland, and European Russia. A smaller ice sheet called the Alpine, centered in the Swiss Alps, covered parts of Austria, Italy, France, and southern Germany. In Asia, ice sheets draped over the Himalayas and blanketed parts of Siberia.

In the Southern Hemisphere, small ice sheets capped the mountains of Australia, New Zealand, and the Andes of South America. Elsewhere, alpine glaciers topped the mountains that are presently ice free. Only Antarctica had a major ice sheet, which expanded to about 10 percent larger than its present size, extending as far as the southern tip of South America.

Excess ice with nowhere to go except into the sea calved off to form icebergs. During the peak of the last ice age, icebergs covered half the area of the ocean. The ice floating in the sea reflected sunlight back into space, thereby maintaining a cool climate with average global temperatures about 5 degrees Celsius colder than today.

Some 10 million cubic miles of water were tied up in the continental ice sheets, which covered about a third of the land surface with an ice volume three times greater than its present size. The accumulated ice dropped the level of the ocean about 400 feet, advancing the shoreline tens of miles seaward. The drop in sea level exposed land bridges and linked continents, spurring the migration of species to various parts of the world. The great weight of the ice sheets caused the continental crust to sink deeper into the upper mantle. Even today, the northern lands are rebounding as much as half an inch per year, long after the weight of the glaciers was lifted.

The lower temperatures reduced the evaporation rate of seawater and lowered the average amount of precipitation, which caused the expansion of deserts in many parts of the world. Fierce desert winds produced tremendous dust storms, and the dense dust suspended in the atmosphere blocked sunlight, dropping temperatures even further. Most of the windblown sand deposits called loess in the central United States were laid down during the Pleistocene ice ages.

The cold weather and approaching ice forced species to migrate to warmer latitudes. Ahead of the ice sheets, which advanced on average perhaps a few hundred feet per year, lush deciduous woodlands gave way to evergreen forests the yielded before grasslands, which became barren tundra and rugged periglacial regions on the margins of the ice sheets.

 

[M82A1]

The Holocene Interglacial:

Perhaps one of the most dramatic climate changes in geologic history took place during the present interglacial period, known as the Holocene epoch. After some 100,000 years of gradual accumulation of snow and ice up to 2 miles and more thick, the glaciers melted away in only a few thousand years, retreating upwards of a half-mile annually. About a third of the ice melted between 16,000 and 12,000 years ago, when average global temperatures increased about 5 degrees Celsius to nearly present-day levels. A renewal of the deep-ocean circulation system, which was shut off or weakened during the ice age, might have thawed out the planet from the deep freeze.

A gigantic ice dam on the boarder of Idaho and Montana held back a huge lake hundreds of miles wide and up to 2,000 feet deep. Around 13,000 years ago, the sudden bursting of the dam sent waters gushing toward the Pacific Ocean. Along the way, the floodwaters carved out one of the strangest landscapes known, called the Scablands. Lake Agassiz, a vast reservoir of meltwater formed in a bedrock depression carved out by glaciers, sat at the edge of the retreating ice sheet in southern Manitoba, Canada.

When the North American ice sheet retreated, its meltwaters flowed down the Mississippi River into the Gulf of Mexico. After the ice sheet subsided beyond the Great Lakes, the meltwater took an alternate route down the St. Lawrence River, and the cold waters entered the North Atlantic Ocean. Simultaneously, the Niagara River Falls began cutting it gorge and has traversed more than 5 miles northward since the ice sheets melted.

The rapid melting of the glaciers culminated in the extinction of microscopic organisms called foraminifera, which met their demise when a torrent of meltwater and icebergs spilled into the North Atlantic. The massive floods formed a cold fresh water lid on the ocean that significantly changed the salinity of the seawater. The cold waters also blocked poleward-flowing warm currents from the tropics, causing land temperature to fall to near ice age levels.

The ice sheets appear to have paused in mid-stride between 13,000 and 11,500 years ago, during a period called the Younger Dryas, named for an Arctic wildflower that grew in Europe. Afterward, the warm currents returned, and the mild weather remained, prompting a second episode of melting that led to the present volume of ice by about 6,000 years ago. Following the receding ice sheets, plants and animals began to return to the northern latitudes.

When the ice sheets melted, massive floods raged across the land as water gushed from trapped reservoirs below the glaciers. While flowing under the ice, water surged in vast turbulent sheets that scoured deep grooves in the crust, forming steep ridges carved out of solid bedrock. Each flood continued until the weight of the ice sheet shut off the outlet of the reservoir. When water pressure built up again, another massive surge of meltwater spouted from beneath and rushed toward the sea. Huge torrents of meltwater laden with sediment surged along the Mississippi River toward the Gulf of Mexico, widening the channel to several times its present size. Many other rivers overreached their banks to carve out new floodplains.

The warming paved the way for the Climatic Optimum, a period of unusually warm, wet conditions that began 6,000 years ago and lasted for 2,000 years. As the Climatic Optimum unfolded, many regions of the world warmed on average about 5 degrees Celsius. The melting ice caps released massive floodwaters into the sea, raising sea levels 300 feet higher than when the Holocene began.

The inland seas filled with sediments, and subsequent uplifting drove out the waters, leaving behind salt lakes. Great Salt Lake in Utah is today only a remnant of a vast inland sea. During a long wet period between 12,000 and 6,000 years ago, it expanded to several times it current size and flooded the nearby salt flats.

 

[M82A1]

Megaherbivore Extinction:

When the last ice age was drawing to a close between 12,000 and 10,000 years ago, an unusual extinction killed off large terrestrial plant-eating mammals called megaherbivores. Woolly rhinos, mammoths, and Irish elk disappeared in Eurasia, and the great buffalo, giant hartebeests, and giant horses disappeared in Africa. Over 80 percent of the large mammals and a significant number of bird species disappeared from Australia.

Meanwhile, the giant ground sloths, mastodons, and woolly mammoths disappeared from North America. A possible exception was the dwarf wooly mammoth, which might have survived in the Arctic until about 4,000 years ago. The loss of these animals also caused their main predators the American lion, saber-toothed tiger, and dire wolf to go extinct.

The global environment reacted to the changing climate at the end of the last ice age with declining forests and expanding grasslands. The climate change disrupted the food chains of many large animals; deprived of their food resources they simply vanished. Also by this time, humans were becoming proficient hunters and roamed northward on the heals of the retreating glaciers. On their journey, they encountered an abundance of wildlife, many species of which they might have hunted to extinction.

In North America, 35 classes of mammals and 10 classes of birds went extinct. The extinctions occurred between 13,000 and 10,000 years ago, with the greatest die-out peaking around 11,000 years ago. Most mammals adversely affected were large herbivores weighing over 100 pounds, many of them weighing up to a ton or more. Unlike earlier episodes of mass extinction, this event did not significantly affect small mammals, amphibians, reptiles, and marine invertebrates. Strangely, after having endured several previous periods of glaciation and deglaciation over the past 2 to 3 million years, these large mammals were unable to survive at the end of the last ice age.

During this time, ice age peoples occupied many parts of North America, and their spearpoints have been found resting among the remains of giant mammals, including mammoths, mastodons, tapirs, native horses, and camels. These people crossed into North America from Asia over a land bridge formed by the draining of the Bering Sea and moved through an ice-free corridor east of the Canadian Rockies.

Instead of migrating to North America in several waves, small bands of nomadic hunters probably crosses the ancient land bridges and ended up in the New World purely by accident. The human hunters arriving from Asia sped across the virgin continent following migrating herds of large herbivores, leaving big game carcasses in their wake.

 

[M82A1]

Glacial Geology:

Much of the landscapes in the northern latitudes owes its unusual geography to massive glaciers that swept down from the polar regions during the last ice age. The power of glacial erosion is well demonstrated in deep-sided valleys carved out of mountain slopes by thick sheets of flowing ice a mile or more thick. The glaciers descended from the mountains and spread across most of the northern lands, destroying everything in their path.

In the alpine regions, glaciers flowing down mountain peeks gouged large pits called cirques. The glaciers extended far down the valleys, grinding rocks on the valley floors as the ice advanced and receded. In effect, a river of solid ice embedded with rocks moved along the valley floors, grinding them down like a giant file as the glacier flowed back and forth over them.

The advancing glaciers left parallel furrows called glacial striae on the valley floors, as they sliced down mountainsides. Miles from existing glaciers are large areas of polished and deeply furrowed rocks, and heaped rocks called moraines mark the extent of former glaciers. Many of the northern lands are dotted with glacial lakes developed from deep pits excavated by roving glaciers.

In other areas, older rocks were buried under thick deposits of glacial till, forming elongated hillocks aligned in the same direction called drumlins. They are tall and narrow at the upstream end of the glacier and slope to a low, broad tail. The hills appear in concentrated fields in North America, Scandinavia, Britain, and other areas once covered with ice. Drumlin fields might contain as many as 10,000 knolls, looking much like row upon row of eggs lying on their sides.

Eskers are long, sinuous sand deposits produced by glacial outwash steam debris. They form winding, steep-walled ridges that extend up to 500 miles in length but seldom exceed more than 2,000 feet wide and 150 feet high. Eskers were probably created by streams running through tunnels beneath the ice sheet. When the ice melted, the old stream deposits remained standing as a ridge. Well-known esker areas exist in Maine, Canada, Sweden, and Ireland.

Rugged periglacial regions existed at the margins of the ice sheets. Periglacial processes sculpted features along the tip of the ice that were directly controlled by the glacier. Cold winds whistling off the ice sheets influenced the climate of the glacial margins and helped create periglacial conditions. The zone was dominated by such processes as frost heaving, frost splitting, and sorting, creating immense boulder fields from once solid bedrock.

The ice age is still with us, only we are fortunate to live in a warmer period between glaciations. Perhaps in another couple thousand years, massive ice sheets will again be on a rampage, wiping out everything they come across. Rubble from demolished northern cities would be bulldozed hundreds of miles to the south, gripped in the frozen jaws of the advancing ice. Global temperatures would plummet, as plants and animals, including humans, scramble for the warmth of the tropics.

The End.

 

[SyntaxVorlon]

You posted a BOOK!???
How original.

 

[victorhadin]

Yeesh. And I thought Willow the Wip was a cut-'n'-paste fanatic. :roll:

 

[Admiral Valdemar]

If you somehow think posting an entire book is going to change anything, guess again.

I have no desire to wade through the masses of text despite my interest in science so I expect no one else to do so either. This is merely an extreme copy & paste debate tactic and has no real worth. I could post every page Dawkins has ever written on evolution or maybe post every page from the Bible, but it'd be ignored and also about as concise as reading out the entire dictionary for someone asking what a Zebra is.

 

[M82A1]

Oh come on! I spent 3 months typing this book down, the least you guys could do is flip through it.

 

[Admiral Valdemar]

Oh come on! I spent 3 months typing this book down, the least you guys could do is flip through it.

Why?

And I did skim through parts of it, but it has no bearing on any argument right now, so it's just fluff that could be called upon in a debate by quoting relevent pages at a time.

 

[SyntaxVorlon]

Oh come on! I spent 3 months typing this book down, the least you guys could do is flip through it.

It may have been a bad idea in the first place, I hope you didn't need permission to post this persons book. Can you post a book about copyright infringement?

 

[M82A1]

Oh come on! I spent 3 months typing this book down, the least you guys could do is flip through it.

It may have been a bad idea in the first place, I hope you didn't need permission to post this persons book. Can you post a book about copyright infringement?

Please. The only way he can sue me is if I sell the book. And I ain't going to be doing that. :wink:

 

[Free]

Pretty sure that just reproducing it without permission is a copyright infringment, whether or not you sell it.

 

[SyntaxVorlon]

Either way it may be best to request a lock.