Geologic Time

Front

What is the oldest and longest period in Earth's history?

Back

Precambrian

Front

What is the current geologic period called?

Back

Holocene

Front

Why is the fossil record incomplete?

Back

All of the above: fossils get eroded away over time, most organisms never became fossils, scavengers and decomposers eat them too quickly.

Front

How old is the Earth?

Back

4.6 billion years

Front

What type of rock do fossils form in?

Back

Sedimentary

Front

What are the three main types of rocks?

Back

Igneous, Sedimentary, Metamorphic

Front

What is the principle of superposition?

Back

In undisturbed sedimentary rock layers, the oldest layers are at the bottom and the youngest are at the top.

Front

What is radiometric dating?

Back

A method used to date materials by comparing the abundance of a radioactive isotope to its decay products.

Front

What is the significance of the Cambrian Explosion?

Back

It marks a period of rapid diversification of life forms on Earth.

Front

What are index fossils?

Back

Fossils of organisms that were widespread but only existed for a short period, used to date rock layers.