Which type of erosion is caused by steady, fast flow of running water?

In the past 500 million years, there have been __________ mass extinctions.

The Wallace Line is generally cited as evidence of which of the following?

Climatologists work to understand what factors affect climate throughout geological time. Scientists have proposed many theories to explain complex climatic events. Which of the following theories explains how shift’s in Earth’s orbit every 100,000 years can trigger ice ages?