Geology Reference
In-Depth Information
Fossils found in rocks provide a long history of life on earth, going back nearly 3.6 billion
years. These early life forms were tiny, single-celled, simple organisms, such as bacteria.
But even at that level, life is a very complicated thing. How did nonliving matter become
living matter? Scientists suspect that energy of some kind acted on chemical elements,
creating the proper combination to spark life. They have even recreated such a scenario
in a laboratory. But until fossil evidence in the rocks is found that can provide clues
about the nature of earliest life, the question is still up for debate.
Mass extinctions
Long after the first life forms existed, earth experienced periods when many different
species thrived, filling the oceans and eventually the land. At least five times in earth's
long history, thousands of species were wiped out in a very short time. (Geologically
speaking, a “short time” can span a few million years; I explain geologic time in Chapter
16.) Such events are called
mass extinctions.
Even if you haven't heard about the other extinctions, you likely know about the extinc-
tion of the dinosaurs. But the extinction of the dinosaurs was not the largest mass ex-
tinction event in earth's history. Hundreds of millions of years before the dinosaurs, an
extinction took place that killed 80 percent of all the plant and animal groups existing at
the time.
In Chapter 22, I describe what is currently known about the mass extinctions in earth's
past. However, geologists and
paleontologists
(people who study fossils) have many un-
answered questions about how and why these periods of major extinction occurred.
Some propose changes in climate as the culprit, and others point to meteor impacts or
extreme volcanic activity. Still others claim only a combination of all these factors could
have led to such dramatic mass extinctions.
Predicting the future: Earthquakes and climate
change
Scientists in many different fields hope someday to understand enough about earth's
systems to be able to predict what changes may occur in the near future. Two examples
I describe here are efforts to predict earthquakes before they occur and the science of
future climate change.
Earthquake warnings
You may have firsthand experience with the literally earth-shaking event of an earth-
quake. If not, you certainly have seen news reports of the terrible devastation that oc-
