The Origin and Evolution of Life

Critical Thinking Activity

Mass extinctions. Thousands of more species than live today have become extinct. Is this normal and natural? For a good discussion of extinction, click here. After you have read the previous article, look at Patterns of Extinction.

Most researchers in the field agree that there were five major extinctions through time. We probably should recognize at least eight. At this Web site you will find all eight listed as additional Web sites of only one page each, except for seven and eight, which are listed together. Click on them all. They are arranged in order, from the oldest to the most recent.

Before we become too captivated by the biological importance of these huge extinctions, let's take a look at Minor Extinctions through the Earth's history.

Of all these events, the one that most engages our attention is the End-Cretaceous, or K-T extinction, because it saw the end of the dinosaurs. Read the Journey to the End of the Dinosaur Era, for a first-hand account of field work by one of the researchers in this subject.

FOR INVESTIGATION: For each inquiry, write your thoughts in a short paragraph for later comparison.

1. In the first paper, Endangered Species Classroom, the importance of determining extinction rates was discussed. Only two sentences were devoted to the problems in establishing extinction rates. Can you think of others?

2. What is the newest hypothesis that seems able to explain catastrophic events among species?

3. Much has been made of catastrophic astronomical events as the cause of mass extinctions. Name the causes given in the list of the eight great extinctions, and note the one that appears most frequently.

4. The dinosaurs likely would have not developed into such a group of such impressive and dominant animals were it not for what event?

Endangered species classroom, Past extinctions

Patterns of Extinction

Mass Extinctions Of The Phanerozoic Menu

Minor Extinctions of Earth History

Journey to the End of the Dinosaur Era: A Society Expedition to Belize