1. How do we know The structure and Age of the Earth

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

3. Radioactive Decay and “Half-Life”
Large unstable (radioactive) atoms decay giving off radiation (energy) and becoming smaller more stable “daughter” atoms.
Uranium becomes… Strontium
Potassium becomes… Calcium and Argon
Carbon 14 becomes… Carbon 12
The time it takes for half of the “mother” atoms to become “daughter” atoms is called the “Half-life” of the radioactive element.

4. The Age of the Earth and the Solar System
By comparing the number of “mother” and “daughter” atoms the age of rocks is determined.
The Oldest rocks on Earth are over 4 billion years old according to this method
Thus the Earth is at least 4.5 billion years old
Further some asteroid fragments found on Earth as meteorites have been dated as 4.6 billion years
Making our Solar System at least that old.