Earth 101 | National Geographic

Earth’s Formation and Structure

Earth formed about 4.5 billion years ago from material left over after the Sun formed. Gravity gathered particles into larger bodies, eventually forming the planet.

Earth’s interior consists of a solid inner core, a liquid outer core, a mantle of flowing silicate rock, and a rocky crust.

Conditions for Life

Earth’s average distance from the Sun—about 93 million miles—helps maintain conditions suitable for liquid water. This contrasts with the colder outer planets and the hotter environment near Mercury.

Earth can hold water as liquid, ice, and vapor. Surface water nourishes land, helps form nutrient-rich soils, gathers into oceans and freshwater systems, and cycles into the atmosphere. The subtitles describe liquid surface water as having cascading effects on Earth and note that life is associated with it.

Life and Biodiversity

Primitive microbial life existed in Earth’s oceans about 3.8 billion years ago. Over time, life diversified across the seas, land, and skies.

Around 1.5 million species have been cataloged, with many more potentially undiscovered. Earth is the only known world to support life.

Researchers or Sources

None are named in the subtitles.