The layers of the atmosphere where gases maintain an approximately uniform composition are the homosphere and heterosphere.

* Homosphere: This layer extends from the Earth's surface up to about 80-100 kilometers (50-62 miles). It is characterized by relatively uniform composition of gases, with nitrogen (N2) and oxygen (O2) being the most abundant.

* Heterosphere: This layer extends above the homosphere and up to the exosphere. Here, the composition of gases varies with altitude, as the lighter gases tend to rise and heavier gases sink due to gravity.

So, in essence, the homosphere is the region where the atmosphere is well-mixed and has a consistent composition.