Geology Reference
In-Depth Information
Another 50 million years later, South America and Africa begin to spread apart, creating
what is now the Atlantic Ocean. By the end of the Mesozoic era the continents looked
very much like they do today, except that India had not yet connected to Asia and
Greenland was still attached to Europe.
Influencing global climate
For the span of human history, the continents have always been in the same place, so it
may never have crossed your mind to wonder what the weather in your region would be
like if the Himalayan Mountains were near Australia instead of between India and China.
But mountains and other features of the earth's surface shape the patterns of wind and
water that circulate weather around the planet. The size of a continent, size of an ocean,
distance from the equator, and elevation of the continent all play a role in global weath-
er patterns today, just as they have in the past.
The breakup of Pangaea dramatically affected the global climate and weather
patterns, creating new environments across the land and beneath the seas. The
changes in climate caused by the breakup of Pangaea are recorded in the Mesozo-
ic rocks. Patterns of two rock types in particular indicate changes in the global cli-
mate patterns during the Mesozoic era.
Evaporites:
Rocks called
evaporites
are created when an area covered by water
dries out. As the water evaporates, minerals form from the elements that were dis-
solved in the water. Mesozoic-aged evaporites are found in regions that were near
the equator between 250 and 65 million years ago, suggesting that the climate near
the equator was especially warm and dry. (This is different from conditions near
the equator today, which are warm and wet.)
Coal:
I explain in Chapter 19 that coal is formed by the accumulation of organic
matter, such as plants, in a warm, tropical region. Prior to the Mesozoic (during
the Carboniferous period, which I describe in Chapter 19), coal deposits were
formed in regions near the equator. But during the Mesozoic, coal layers began to
form much closer to the poles, suggesting that after the Paleozoic glaciers melted,
temperatures at the North and South Pole were fairly warm.
Scientists generally accept that the Mesozoic climate was moderate and warm. Some sci-
entists think that the movement of landmasses away from the equator toward the poles
began to create a temperature gradient similar to, but not as extreme as, the one that ex-
ists today. (A
temperature gradient
describes how the temperatures get cooler as you
