The Earth’s history

As the proto-Earth grew, heavier elements within it began to sink toward the center, forming the core, and lighter elements rose to the surface. This process, called differentiation, likely took place over tens of millions of years.

During these early stages a Mars-sized protoplanet, often referred to as Theia, collided with the young Earth, ejecting material from both protoplanets into space. Some of this material fell back to Earth, but some of the material eventually coalesced in orbit around Earth to form the Moon.

The Earth continued to experience impacts throughout its early life, though none as dramatic as the collision with Theia. During a period called the Late Heavy Bombardment, which likely happened between 4.1 and 3.8 billion years ago, there was an increased rate of asteroid and comet impacts in the inner Solar System. The Late Heavy Bombardment had major geological consequences, including causing Earth’s crust to melt and differentiate and shaping the early atmosphere and oceans. Although geological activity has erased the craters from this time on Earth, they are preserved on the Moon. These are some of the craters you can see from Earth.

By about 4.3 billion years ago, the Earth's surface had cooled enough for water vapor in the atmosphere to condense on the surface, leading to the formation of oceans. Volcanic activity, which was more widespread at the time, released gasses that shaped the early atmosphere. Life emerged around 3.5 to 4 billion years ago in the form of simple, single-celled organisms.

The Earth has probably been as we know it today — with recognizable continents, oceans, a hospitable climate, and diverse life — for the past few hundred million years. But it continues to evolve through its own gradual tectonic and volcanic activity, and through the more rapid effects of climate change.