To establish the age of a rock or a fossil, researchers use some type of clock to determine the date it was formed. Geologists commonly use radiometric dating methods, based on the natural radioactive decay of certain elements such as potassium and carbon, as reliable clocks to date ancient events.

How do you tell rocks from oldest to youngest?

The law of superposition states that rock strata (layers) farthest from the ground surface are the oldest (formed first) and rock strata (layers) closest to the ground surface are the youngest (formed most recently).

How old is our planet?

4.543 billion years Earth/Age

How can you tell which rock layer is older?

The bottom layer of rock forms first, which means it is oldest. Each layer above that is younger, and the top layer is youngest of all.

Can a rock be broken?

Erosion happens when rocks and sediments are picked up and moved to another place by ice, water, wind or gravity. Mechanical weathering physically breaks up rock. Over time pieces of rock can split off a rock face and big boulders are broken into smaller rocks and gravel.

Are extrusions older or younger?

The rock layers below an extrusion are always older than the extrusion. Beneath the surface, magma may push into bodies of rock. There, the magma cools and hardens into a mass of igneous rock called an intrusion. An intrusion is always younger than the rock layers around and beneath it.