Geography Reference
In-Depth Information
Populating the Planet
Perhaps the greatest migration story of them all involves the populating of the planet. Scientific evid-
ence suggests humans originated in East Africa. The Bible talks of the Garden of Eden, somewhere
in Mesopotamia. Either way, the basic argument is that
homo sapiens
began by occupying one very
small part of planet Earth.
Thatdidn'tlast.WhenColumbusreachedtheNewWorld,hediscoveredthatotherhumanshadgotten
there long before he did. Throughout the Age of Discovery, other explorers also found that, time and
again, other humans had beaten them to their newly found lands. Throughout the Americas, the Pa-
cific Islands, the far Northlands, Eurasia, Africa, Australia, and New Zealand, you name it. Humans
were just about everywhere except Antarctica. How had they done it? That is, assuming humans ori-
ginated in a single region (and no credible evidence has been found to the contrary), how had they
managed by 1492 to assume a near-global distribution? The answer is land bridges and ocean voy-
ages.
Bridging the oceans
Onceuponatimeitwaspossibleforhumanstowalkbetweencertaincontinentsandotherlandbodies
that are today separated by straits and shallow seas. The key word in that sentence is walk — and on
dry land, too. That was made possible by something rather peculiar that happened during the last ice
age.
Earth has experienced several ice ages during the past million years. We're not certain what caused
them, but climates then were definitely cooler on average than they are today. The most recent ice age
began about 120,000 years ago and ended about 10,000 years ago. During that period, humongous
amounts of seawater evaporated, condensed in the atmosphere, fell to Earth as snow, and compacted
to form glaciers instead of returning to the sea as runoff. Thus, as the glaciers grew, sea level dropped.
The exact extent of the decline is unknown, but for several thousands of years sea level was as much
as 475 to 500 feet lower than today.
Thus, a world map at the height of the ice age would have looked a lot different from today's (see
Figure 12-1). Substantial areas that had been ocean bottom became dry land, so the continents and
other land bodies grew while the oceans shrank. Most importantly, several land bodies that had been
separated by water became connected by
land bridges
— dry land in places that had been straits or
shallow seas.
