1. Science Earth’s Changing Surface
Chapter 4
Section 3

2. Radioactive Dating Everything around us is made up of matter
Matter is made up of tiny particles called atoms
When atoms in a particular type of matter are the same, the matter is an element
There are about 110 elements
Most elements are stable
They do not change under normal conditions

3. Continued Some elements exist in forms that are unstable
These may break down or decay, & in the process release particles & energy in a process called radioactive decay
These unstable elements are said to be radioactive
During this decay, the atoms of one element break down to form atoms of another element.

4. The Rate of Radioactive Decay
As a radioactive element w/i the igneous rock decays, it changes into another element.
So, the composition of the rock changes slowly over time
The amt of the radioactive element goes down, but the amt of the new element goes up
*the rate of decay of each radioactive element is constant—it never changes.
This rate of decay is the element’s half-life.
This is the time it takes for half of the radioactive atoms to deday

5. Absolute Ages from Radioactive Dating
Geologists use radioactive dating to determine the absolute ages of rocks.
First, the amt of radioactive element in a rock is determined
Then a comparison this amt to the amt of the stable element into which the radioactive element decays
Types of dating
Potassium-Argon Dating—used to date rocks
Carbon-14—useful for dating plants & animals up to 50k years ago

6. Radioactive Dating of Rock Layers
RA cannot be used in dating other than igneous rocks
For sed rocks scientists date the intrusion & extrusions nearby.
E has been dated to about 4 billion years
May be older