The third layer of the atmosphere is the Mesosphere. The mesosphere starts at 50 km above ground and goes all the way up to 85 km. Most meteors burn up in this layer. The forth layer of our atmosphere is the thermosphere. Strange,high-altitude clouds called noctilucent clouds sometimes from in this layer near the North and South poles. Temperatures climb sharply in the lower thermosphere (below 200 to 300 km altitude), then level off and hold fairly steady with increasing altitude above that height. The last layer of our atmosphere is the exosphere. The region where atoms and molecules escape into space is referred to the exosphere. One definition of the outermost limit of the exosphere places the uppermost edge of Earth's atmosphere around 190,000 km (120,000 miles), about halfway to the Moon.