The vast majority, approximately 99%, of the Earth's atmospheric mass is concentrated within the first 20 miles (32 km) above the planet's surface.
The Density of the Lower Atmosphere
The air surrounding our planet doesn't extend infinitely with uniform density. Instead, gravity pulls most of the atmospheric gases closer to the Earth's surface. This results in the air being much denser at lower altitudes and becoming progressively thinner as you ascend.
According to the reference provided (Atmospheric Structure www.albany.edu), "About 99% of the total atmospheric mass is concentrated in the first 20 miles (32 km) above Earth's surface." This highlights just how quickly the atmosphere thins out with increasing altitude.
Atmospheric Mass Distribution
This concentration means that while the atmosphere extends much higher (hundreds of miles), almost all of the actual material that makes up the air we breathe and that creates atmospheric pressure is found relatively close to the ground.
Here's a simple breakdown based on this fact:
| Altitude Range | Approx. % of Total Atmospheric Mass |
|---|---|
| 0 to 20 miles (32 km) | ~99% |
| Above 20 miles (32 km) | ~1% |
This dramatic drop-off in density is why phenomena like weather primarily occur in the lowest layer, and why climbing high mountains or traveling in aircraft requires supplemental oxygen – there's simply not enough air to breathe comfortably at those altitudes.
