Main Page | See live article | Alphabetical index The exosphere is the uppermost layer of the atmosphere. On Earth, its lower boundary is estimated at 500 km to 1000 km above the Earth's surface, and its upper boundary at about 10,000 km. It is only from the exosphere that atmospheric gases can, to any appreciable extent, escape into outer space. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.