Mass extinctions are periods in Earth's history when abnormally large numbers of species die out simultaneously or within a limited time frame. The Cretaceous-Tertiary (or K-T) extinction event is probably the best known to many people because it wiped out the dinosaurs, but many other mass extinction events have occurred throughout the history of the Earth. Some of these mass extinction events are even more devastating than K-T. The most severe occurred at the end of the Permian period when approximately 96% of all species disappeared. Many smaller-scale mass extinctions of plants and animals have occurred as recorded in the fossil records.

Consider the history of extinction on our planet. From the Sam Noble Museum, answer the following questions:

1. How many major mass extinction periods are listed here? Follow the links from that page to learn more about each period. What caused each, and which major groups of species disappeared from each period? Choose two of the recent extinctions listed on this link and explain why they occurred.

2. Global Climate Change Scientists have concerns that human activities are changing our environment at rapid rates that could result in a sixth mass extinction. Let’s examine the evidence: Review the “Recent, Past and Present” section from Mass Extinctions. Also review the following link from the NASA website: https://climate.nasa.gov/causes/

Define greenhouse effect. Describe which gases are important to the greenhouse effect.

What were listed as human activities related to greenhouse gas production from each link?

How do humans contribute to both climate change and major extinction events?

Some scientists think that human activities may be contributing to a sixth mass extinction event. What specific evidence do they site for this possible event? (you may need to conduct additional research to support your findings).

3. Drawing Conclusions Now provide a summary paragraph that explains what conclusions you can make for yourself based on the evidence provided and what you now know about the geologic time scale of the history of the Earth.