At 40,000 feet altitude, you are in the troposphere, the lowest layer of Earth's atmosphere.

Here's why:

* Troposphere: Extends from the Earth's surface to about 7-15 km (4.3-9.3 miles) high. This layer contains most of the atmosphere's mass and is where we experience weather phenomena.

* Stratosphere: Lies above the troposphere and extends to about 50 km (31 miles) high. This layer contains the ozone layer, which absorbs harmful ultraviolet radiation from the sun.

Since 40,000 feet is roughly 12.2 km, it falls within the range of the troposphere.