years ago
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North Pole
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225 million years ago
South Pole
tion of the southern Appalachians. By about 225 million years ago, at the close of the Paleozoic Era, Pangaea was one vast landmass that stretched from pole to pole. Virtually all of the Earth's continental lithosphere remained joined together for the next 50 million years or more, until Pangaea began to rift and water flowed in to form the modern oceans.
Continental Rises
Laurentia (North America) collided with Baltica (northern Europe) and later with Avalonia (Britain and New England), a fragment of Gondwana. The Caledonian mountains and northern Appalachians were thrust up along the boundary. As the continents squeezed together, ocean basins widened and sea level fell,
uncovering more land and withdrawing saltwater barriers between rivers and lakes. Freshwater fish migrated freely, and plants colonized land. Later, as carbon-rich vegetation was buried, carbon dioxide levels in the atmosphere fell, allowing Earth to cool.
A chunk of Pannotia tore off and drifted north, leaving the continent of Gondwana at the South Pole. As the fragment approached equatorial latitudes, it splintered into three parts that were mostly submerged. Between lay warm, shallow seas
where multicellular animals exoskeletons first appeared million years ago.The sudde abundance of fossil evidenc three billion years of primiti is called the Cambrian explc
ARS AGO
Apart
ieces collided itinent of Panák up, rifting isia-North h America, and India. Next, ars ago, each ed, perhaps plumes rising i fragmentation ' lines such as ed a warm cli-vlewly formed placed seas, vith heat-le shallow 3nts carried )ward the Poles.
ARS AGO
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e dinosaurs tem-
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SO MILLION YEARS AGO
High and Dry
Pangaea's breakup ended and a new cycle of continental collision began. Africa hit Europe, and India rammed into Asia, thrusting up the Alps and Himalaya. Continental compression led to widened ocean
basins, which lowered sea level. Migration routes emerged, and land animals flourished. But greater expanses of heat-reflecting land helped cool Earth and allowed ice to remain year-round in Antarctica.
clear only in this century, with the tectonics.
First attempts at reconstructing based on the incomplete theory of
led. But greater ecting land rl allowed ice in Antarctica.
Freeze
At the peak cf the last great ice age glaoers frosted northern Europe
ticľwa:Nľrth/merÍCa'andAntarc-t.ca Water locked in ice transformed
fam.l.ar continental outlines, lowTr'no sea eve. 300 to 500 feet and ex^os ng oontmentai Reives and a iand bridge
from Asia to the Americas. WithinTe
next 8,000 years the glaciers receded, the oceans rose, and the climate turned warmer and wetter. Along -ts farthest margin the retreating
the Great Lakes, pressed into the lanascape.
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g the 3, ice
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10,000 YEARS AGO
1,000 YEARS AGO
SHAFTS INTO THE PAST
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an, ancestor of the Pacific. The rged ocean basin caused sea ! to falf, whife the north-south
Pangaea, evolving into diverse forms that gave rise to the dinosaurs.