Earth is the third planet from the sun and the only known place to support life. Earth sciences study the solid Earth, its waters, and atmosphere in order to understand Earth's features and evolution. The lithosphere is Earth's solid outer layer including the upper mantle and crust. Earth's hydrosphere includes all water on the planet in liquid, vapor, or ice form in oceans, lakes, rivers, underground, and air. The atmosphere helps make life possible by providing air, shielding from UV rays, trapping heat, and preventing extreme temperature differences. The biosphere is where life exists on Earth from root systems to ocean trenches to rainforests and mountaintops.