AP BIOLOGY

Detailed explanation-1: -Until this development, all life on Earth must have existed either under at least several centimeters of water or underground. The ozone layer, which blocks most of the damaging ultraviolet light from the Sun, did not exist, so any organism on the surface of the Earth would have been killed by the ultraviolet light.

Detailed explanation-2: -The early Earth had no ozone layer and was probably very hot. The early Earth also had no free oxygen. Without an oxygen atmosphere very few things could live on the early Earth.

Detailed explanation-3: -The early Earth had no atmosphere or free water. The planet was far too hot for gases and water to collect. The gases came from volcanic eruptions and from comets. Nitrogen, carbon dioxide, hydrogen, and water vapor, or water in gas form, were in the first atmosphere.

Detailed explanation-4: -Earth’s first atmosphere came from outgassing from the planet’s interior and from asteroids and comets from elsewhere in the solar system. Earth’s first and second atmosphere did not contain oxygen so there was no ozone layer to protect life from ultraviolet radiation and no oxygen for animals to breathe.

Detailed explanation-5: -(4.6 billion years ago) When Earth formed 4.6 billion years ago from a hot mix of gases and solids, it had almost no atmosphere. The surface was molten. As Earth cooled, an atmosphere formed mainly from gases spewed from volcanoes.