Question

What attaches itself to this jet stream and, in a sense, tells you where the stratosphere begins? (hint: it protects us from the sun's uv rays)?

Answer 1

Ozone molecules.

Ozone is a gas that is naturally present in our atmosphere, mostly in a region of the stratosphere, also known as the ozone layer. It's  between about 10 km and 50 km above the surface of the earth and extends over the entire globe with some variation.
The ozone in the stratosphere is considered good  because it absorbs ultraviolet- B (UV-B) radiation from the Sun . If not absorbed, radiation would reach Earth’s surface in  higher amounts that would be more harmful.