present levels, so landmasses we would not recognize today
remained above water. One of these was the sprawling land-
scape of Beringia, an area encompassing parts of modern-day
Alaska and easternmost Siberia. Th is landmass provided an
inhospitable yet solid land bridge between Russia and North
America. Siberian hunter-gatherers on the trail of large prey,
such as mammoth, musk ox, and saiga antelope, could have
crossed some 60 miles of open tundra into Alaska. Th ere,
they gradually would have become stranded by rising sea lev-
els. Th ey might have settled near Beringia’s rivers for an easy
supply of fresh water but would eventually have moved on
in search of territories more fertile than this dry scrub land.
As the ice age ended, much of Beringia became submerged
beneath the icy waves of today’s Bering Sea. Ocean levels con-
tinued to rise.
Th e submergence of the Bering Strait (the narrow pas-
sage between modern-day Alaska and Siberia) took many
generations, so the new settlers would have had an oppor-
tunity to return to the Siberia of their forbears. It is possible
that some did rejoin their countrymen on the Russian side
of Beringia, but today’s Native Americans are descendants of
the ones who attempted to push farther and farther into the
new territory.
Once they were in North America, their path to the rest
of the continent was not yet clear. Glaciers still covered much
of Alaska and Canada so that these early Americans may
have lived for centuries trapped between their submerged
land bridge to the north and Canada’s glacial ice sheets to
the south. In the unstable climate the ice sheets sometimes
convulsed violently, occasionally advancing toward the set-
tlers. As they did so, the glaciers slowly crushed and envel-
oped entire forests, diminishing vital habitat and destroying
food and shelter. Oft en the ice would suddenly retreat again,
leaving a fl attened landscape in its wake. Even in times of
retreat, glacial meltwaters could inundate grazing land and
woodlands and cause massive fl ash fl ooding as millions of
cubic tons of water came bursting out from behind dams
of half-melted glacial ice. Enormous boulders and jagged
chunks of ice tumbled within these fl oods, smashing every-
thing in their path.
It was a millennium or more before the two major Ca-
nadian ice sheets, the Cordilleran in the west and the Lau-
rentide in the east, parted and permitted the new settlers to
enter the rest of the Americas. From there the migrants di-
versifi ed into more than 2,000 societies with more than 1,000
languages and produced some of the greatest civilizations in
human history.
It is apparent from studies of Native American lan-
guages and DNA that American settlement began with
migrants from Siberia. Th e linguist Joseph Greenberg and
other scientists have proved that ancient America was set-
tled not by just one but by several separate waves of east-
ward migration from Asia. Greenberg had been suggesting
since the 1950s that Native American languages fell into
three distinct families. By the 1980s, aft er many years of
collaboration and comparison among several disciplines,
scientists were able to demonstrate that North America
had been settled in three separate waves: Paleo-Indians
had arrived near the end of the last ice age and spawned
the majority of native languages, a second group consisting
of Na-Dene speakers (the Athabascan family from whom
the Apache and Navajo descend) arrived some 9,000 years
ago, and just 4,000 years ago a fi nal group arrived speaking
a language from which modern Inuit (Eskimo) and Aleut
have developed. Discovering the exact means by which
these later migrants arrived, whether by land or sea, has
become a new quest of archaeologists.FROM BERINGIA TO CLOVIS
By the time they were cut off from their Siberian heartland
the ancient Alaskan settlers had already begun to adapt to
their new home. Diff erent bands of settlers quickly diversi-
fi ed into distinct hunting, fi shing, and foraging cultures in
reaction to their maritime, tundra, valley, or highland envi-
ronments. As they began to diff er from each other, they also
diff ered considerably from their Siberian relatives in culture,
technology, and language. Anthropologists call these distinct
people Paleo-Indians (“ancient Indians”) to distinguish them
clearly from their Asian antecedents. For some 2,000 years
they may have lived confi ned to northwestern Canada, but
as the ice age ended and the Cordilleran and Laurentide ice
sheets fi nally melted, the new settlers were free to issue forth
into the vast American landscape.
Th e oldest sites in North America south of the ice sheets
are located in the western United States. Th e sites of Folsom
and Clovis in New Mexico date back as far as 11,000 and
11,500 years ago, respectively. At both of these sites stone
projectile points from spears and arrows were found among
the bones of extinct ice age mammals, indicating that people
had been in America at least 10,000 years ago. In fact, the
fi nely wrought projectile points had been found between the
ribs of a bison skeleton at Folsom and between the ribs of
several mammoths at Clovis. Th us these ancient “kill sites”
contained diff erent prey and slightly diff erent kinds of pro-
jectiles but illustrated similar hunting techniques. Th e Clo-
vis and Folsom people appeared to be hunter-gatherers who
stalked large prey that would supply them with large amounts
of food at a time, which they could eat on the spot or preserve
until the next hunt.
When radiocarbon dating was introduced in the 1950s,
almost two decades aft er the fi rst excavations at Folsom, it
was determined that Clovis was the older site. All biological
organisms absorb carbon isotopes while they are alive. Some
of these isotopes decay at a steady rate aft er an organism’s
death. Radiocarbon (or carbon 14) testing measures the de-
gree of isotopic decay to approximate the year or period of
death of an organism. Radiocarbon dating is commonly used
to fi x the age of artifacts in conjunction with other contex-
tual information, such as location, materials, and methods of
manufacture. Although varying designs of projectile points720 migration and population movements: The Americas