The hottest layer is in The tropopause. The tropopause is the boundary between the troposphere and the stratosphere. The tropopause is located at 15 to 35 kilometers (9 to 22 miles) above the Earth’s surface. The tropopause is the coldest part of the atmosphere. The tropopause is a band that marks the boundary between the lower atmosphere and the upper atmosphere. The tropopause is the coldest part of the entire Earth’s atmosphere. The tropopause is the lowest altitude where clouds form. The tropopause is located at an altitude of 15 to 35 kilometers (9 to 22 miles) above the surface of the Earth.