First North Americans (03:11)
When humans first migrated from Africa to North America, much of the continent resembled Alaska's Mendenhall Glacier. After scaling the side of a glacier, Kirk Johnson doubts that the first Americans crossed the northern ice sheet.
Arlington Man (03:38)
When the climate warmed 13,000 years ago, a corridor opened allowing passage into the continent. Johnson and Joe Watkins investigate some of the earliest human remains in North America, found on Santa Rosa Island.
California's Tar Pit (02:31)
The use of boats could have opened the way for early inhabitants to settle along the western edge of the continent. Johnson visits the La Brea Tar Pits, a fossil site revealing an ancient hunting ground.
Stone Age Tool-Kit (03:08)
For Ice Age hunters, mammoths were of high value. Johnson travels to Boulder, Colorado to investigate the type of weapons these hunters used. North Americans relied on stone.
Conquering the Continent (03:06)
The most lethal hunting weapon early North Americans devised was a spear tip known as a Clovis point. Johnson and Bob Patten create a Clovis point replica, and test its killing power.
Hunters and Farmers (04:08)
By 12,000 years ago, mammoths, saber-tooth cats, dire wolves, and camels had all but disappeared, leaving the bison to flourish in the Great Plains. Johnson visits Cliff Palace in Mesa Verde, Colorado.
Natives and Colonists (01:58)
Early Americans in Cahokia, Illinois, raised corn to support a city of 15,000. Hundreds of thousands lived in the Aztec capital in central Mexico at the end of the 15th century. Western Europeans opened up the corridor for conquerors, colonists and their slaves, who would displace most of the native population.
Colonial Agriculture (04:08)
David Montgomery explains the definition and historical significance of soil. For 10,000 years nature had been preparing the soil along the Southeast coast for tobacco cash crops. Montgomery compares forest soil and tobacco field soil.
Fertile Lands and the Gold Rush (02:04)
During the westward expansion, the Great Plains and gold were discovered. In 1848, Mexico ceded to the US a territory that would later become California. In 1949, 80,000 people joined the gold rush.
Formation of Gold (03:43)
Johnson and Lisa White visit a historically persevered mine in the Sierra Nevada Mountains. Gold rises to the earth's surface through pathways created from earthquakes.
Gold Fever (01:50)
Between 1848 and 1860, it is estimated that more than one million pounds of gold were found in the hills of California. Johnson visits an old mint called the Granite Lady, where gold was turned into coins.
Transcontinental Railroad (03:08)
By the 1860s, the American economy was industrialized and the steam locomotive was invented. In 1863, the US government launched the Transcontinental Railroad project. With the two coasts linked, the economy boomed.
Discovering Black Gold (03:40)
Johnson travels down into a fossil tar pit to see Los Angeles's black gold. Oil is produced by the slow accumulation and burial of marine plankton over millions of years. LA has more than 3,000 active oil wells.
Ghost Forest (02:11)
When fossil fuels are burned, the release of carbon dioxide causes earth's atmosphere and oceans to warm. The Pacific Northwest offers clues of a potential natural disaster.
Natural Disaster (03:02)
Johnson and Brian Atwater carve into the mud to reveal three distinct layers. In 1700, the activity of the Cascadia Subduction Zone created massive land transformation.
Living on Borrowed Time (03:34)
At Oregon State University, Chris Goldfinger studies deep-sea earthquakes that can cause tsunamis. A severe earthquake strikes somewhere along the fault line about every 240 years. Johnson describes what geologists predict will happen to North America in the next 175 million years.
Credits: Human: Part 3—Making North America (01:36)
Credits: Human: Part 3—Making North America
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