Science Olympiad Dynamic Planet Practice Test

What is isostasy?

1. A process of ice sheet formation

2. A state of gravitational equilibrium between Earth's crust and mantle

3. A method of measuring geological time

4. A type of geological fault

The correct answer is: A state of gravitational equilibrium between Earth's crust and mantle

Isostasy refers to the state of gravitational equilibrium that exists between the Earth's crust and the mantle. This concept explains how sections of the Earth's crust "float" on the more fluid mantle beneath them. The idea is that the lithosphere, which includes the crust, is less dense than the underlying asthenosphere, allowing it to rise or sink to create balance in response to changes such as erosion, sediment deposition, or tectonic activity. Isostatic adjustments occur when these changes take place, resulting in vertical movements of the Earth's surface. For example, when large ice sheets melt, the crust, which had been depressed by the weight of the ice, slowly begins to rise again in a process known as post-glacial rebound. Understanding isostasy is crucial for geologists as it helps to explain various geological formations and processes, as well as the distribution of tectonic plates.