The part of the atmosphere that protects Earth from ultraviolet radiation is the stratosphere, specifically the ozone layer.

Here's why:

* Ozone Layer: The ozone layer is a region within the stratosphere that contains a high concentration of ozone (O3) molecules. Ozone is a powerful absorber of ultraviolet (UV) radiation.

* UV Radiation: UV radiation is a type of electromagnetic radiation that can be harmful to living organisms. It can cause skin cancer, cataracts, and damage to plant life.

* Absorption: When UV radiation enters the atmosphere, it collides with ozone molecules. This collision causes the ozone molecules to absorb the UV energy and break down into oxygen molecules (O2) and single oxygen atoms (O). This process prevents the harmful UV radiation from reaching the Earth's surface.

So, while the entire atmosphere plays a role in protecting us from space, the ozone layer in the stratosphere is the primary shield against harmful UV radiation.