What is the uppermost later of the atmosphere?

The uppermost layer of the atmosphere is the exosphere. It extends from about 600 kilometers (373 miles) above the Earth's surface to around 10,000 kilometers (6,200 miles) and gradually transitions into outer space. In this layer, the atmosphere is extremely thin, and particles are so sparse that they can travel long distances without colliding with one another. The exosphere contains low-density hydrogen and helium, along with some heavier molecules.