What is the name of the fifth layer of the atmosphere?

The fifth layer of the Earth's atmosphere is called the exosphere. It extends from around 600 kilometers (about 370 miles) above the Earth's surface to about 10,000 kilometers (6,200 miles). This layer is characterized by extremely thin air, where particles are so sparse that they can travel hundreds of kilometers without colliding with one another. The exosphere gradually transitions into outer space.