Question

Which events contributed to life evolving on Earth? Check all that apply.

Organisms began to photosynthesize.
The surface cooled, and water condensed.
Volcanoes added carbon dioxide to the atmosphere.
Ozone formed and blocked ultraviolet rays from the Sun.
Comets crashed into Earth, releasing water.

Answer 1

All five statements contributed. Briefly:

- Organisms began to photosynthesize — yes. Photosynthesis produced oxygen, enabling aerobic metabolism and later complex life.
- The surface cooled, and water condensed — yes. Liquid water (oceans) was essential for biochemical reactions and early life.
- Volcanoes added carbon dioxide to the atmosphere — yes. Volcanic outgassing created an atmosphere and greenhouse gases that helped keep the planet warm and supplied key chemicals.
- Ozone formed and blocked ultraviolet rays from the Sun — yes. The ozone layer (produced after oxygen built up) protected organisms from harmful UV, allowing life to spread toward the surface and land.
- Comets crashed into Earth, releasing water — yes. Impacts likely delivered significant water and organic compounds that helped seed Earth’s oceans and prebiotic chemistry.