Extinction may be constructive in a Darwinian sense or it may only perturb the system by eliminating those organisms that happen to be susceptible to geologically rare stresses. A drop in sea level and climatic change are most frequently invoked to explain mass extinctions, but new theories of collisions with extraterrestrial bodies are gaining favor. Most extinction episodes are biologically selective, and further analysis of the victims and survivors offers the greatest chance of deducing the proximal causes of extinction. Extinction may be episodic at all scales, with relatively long periods of stability alternating with short-lived extinction events. The five largest mass extinctions of the past 600 million years are of greatest interest, but there is also a spectrum of smaller events, many of which indicate biological systems in profound stress. For this reason alone, extinction must play an important role in the evolution of life. Students will complete 3 short answer questions based on the reading. In this fossils learning exercise, learners will read about the discovery of fossil leaves by Edward Golenberg.
Virtually all plant and animal species that have ever lived on the earth are extinct. This Middle and Recent Earth History Worksheet is suitable for 7th - 12th Grade.
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