Earth formed about 4.5 billion years ago from material left over from the formation of the young Solar System. Dust and rock around the young Sun gradually collided, stuck together, and grew into larger bodies.

Over millions of years, these bodies merged through accretion—the gradual buildup of a planet by collecting more material. Eventually, one of these growing worlds became Earth.

Earth Began in the Young Solar System

A Disk of Dust and Rock Surrounded the Young Sun

The Solar System began as a cloud of gas and dust that collapsed under gravity. As it collapsed, much of the material formed a rotating protoplanetary disk, a disk of gas and dust surrounding the young Sun.

In the hotter inner part of this disk, rocky and metallic materials could remain solid. These materials became the main building blocks of Earth and the other rocky planets.

Dust Grains Began Building Larger Bodies

From Dust to Planetesimals

Tiny grains of solid material collided inside the disk. Some collisions allowed particles to stick together, producing larger clumps, pebbles, and rocks.

As these objects grew, gravity became increasingly important. They eventually formed larger bodies called planetesimals, which became the building blocks of planets.

Gravity Accelerated the Growth

Larger bodies had stronger gravity, so they could attract more material. Repeated collisions gradually made them larger.

Some eventually became planetary embryos—large developing bodies that could continue collecting material. Earth grew from this process of repeated accretion.

Earth Grew Through Accretion

Planetary Embryos Collided and Merged

Earth was not built in one collision. It grew as planetary embryos and other rocky bodies repeatedly struck and merged with the developing planet.

Some impacts destroyed or scattered material, while others added material to Earth. Over time, these repeated events increased Earth’s size and mass.

Earth’s Growth Was Violent

As Earth became larger, some collisions involved increasingly massive bodies. The energy released by these impacts helped heat the young planet.

Scientists reconstruct this violent stage from evidence preserved in Earth, the Moon, meteorites, and other rocky bodies, combined with models of planetary formation.

The Young Earth Became Extremely Hot

Where Did Earth’s Heat Come From?

Earth’s early heat came mainly from the energy of impacts, compression as gravity squeezed the growing planet, and radioactive elements inside it.

As the temperature increased, parts of the young Earth became molten or partially molten. This allowed different materials to move through the planet.

Earth Separated Into Layers

Heavy Metals Sank Toward the Center

When the young Earth was hot and able to deform, dense metals such as iron moved downward toward the center.

Less-dense rocky material remained above them. This process is called planetary differentiation.

Earth’s Basic Internal Structure Took Shape

Differentiation produced the basic structure of Earth: a metal-rich core, a rocky mantle, and a crust.

This was one of the most important steps in Earth’s early development.

Earth Became the Planet We Know Today

A Young Planet Still Undergoing Change

After its main growth, Earth was still a young and changing planet. It continued to cool and evolve while impacts and volcanic activity reshaped its surface.

The Earth we know today developed through processes that continued long after the planet itself had formed.

What Happened After Earth Formed?

Earth’s formation was only the beginning. Its atmosphere developed through later processes, water accumulated through a combination of sources and processes, and the Moon formed during Earth’s early history.

These stages deserve their own explanations, so they are covered in the upcoming articles How Did Earth Get Its Atmosphere?, How Did Water Come to Earth?, and How Did the Moon Form?

Conclusion

Earth formed through accretion, collisions, heating, and planetary differentiation.

Dust and rock became planetesimals, planetesimals helped build planetary embryos, and repeated collisions produced a growing Earth. As the young planet heated, dense metals moved inward while lighter rocky material remained above, creating Earth’s basic internal structure.