1. How we know the structure and age of Earth
5.2(b) - Earth’s Interior
How we know the structure and age of Earth

2. Seismic waves reveal Earth’s Structure
There are three kinds of seismic ( aka earthquake) waves.
They reflect and refract differently in the different layers of the Earth.
Scientists study them to determine Earth's structure.

3. Radioactive Decay and “Half-Life”
Large, unstable (radioactive) atoms decay, and give off radiation (energy). They become smaller more stable “daughter” atoms.
Uranium becomes… Strontium
Potassium becomes… Calcium and Argon
Carbon 14 becomes… Carbon 12

4. The time it takes for half of the “mother” atoms to become “daughter” atoms is called the “Half-life” of the radioactive element.

5. The Age of the Earth and Solar System
The age of a rock is determined by comparing the number of “mother” and “daughter” atoms in a sample.

6. According to this method, the oldest rocks on Earth are over 4 billion years of age, which makes the Earth itself at least that old.

7. 4.6 million year old meteorite, in China.
Some asteroid fragments found on Earth have been dated as 4.6 billion years old, making our Solar System about that age, as well.
4.6 million year old meteorite, in China.