The four most abundant gases in the Earth's atmosphere are:

1. Nitrogen (N2): Makes up about 78% of the atmosphere.

2. Oxygen (O2): Makes up about 21% of the atmosphere.

3. Argon (Ar): Makes up about 0.93% of the atmosphere.

4. Carbon Dioxide (CO2): Makes up about 0.04% of the atmosphere.

It's important to note that there are many other trace gases present in the atmosphere, but these four make up the vast majority.