First Billion Years of Earth (David Wang)

Beginning of the Formation of the Milky Way

1360 BCE

Astronomers believe that the galaxy formed out of a large, fairly spherical cloud of cold gas, rotating slowly in space. At some point in time, the cloud began to collapse in on itself, or condense, in the same way that the clouds which formed individual stars also condensed.

Beginning of Formation of Earth (Planetary Accretion)

454 BCE

While scientists disagree on the details, most researchers think Earth formed by a series of collisions that took place less than 100 million years after the solar system coalesced. More than 10 impacts with other bodies added bulk to our growing planet, according to most models of Earth's formation. By measuring the age of rocks on the moon, and meteorites found on Earth, scientists estimate the Earth consolidated by 4.54 billion years ago.

Earth-Moon Collision (Formation of the Moon)

451 BCE

The final collision in Earth's timeline was with Theia, a rocky planetoid perhaps the size of Mars. This protoplanet sideswiped Earth, leaving our planet mostly intact but destroying itself and blowing away Earth's atmosphere. Theia's vaporized debris condensed into Earth's moon. Some researchers think remnants of the pre-collision Earth still exist deep in Earth's mantle and outer core today. The mantle is the layer between the surface crust and the core.

Planetary Cooling (after impact)

440 BCE

The force of the moon-forming impact left Earth a churning hot magma blob. The hellish conditions meant Earth resembled Venus for a time, with a hazy, steamy atmosphere. But as the planet cooled, lava became rock and liquid water started to condense, forming Earth's first ocean. The oldest minerals found on Earth, called zircons, date back to this time and are 4.4 billion years old.

End of Heavy Bombardment

380 BCE

Early Earth suffered constant threat of attack from leftover planet-building material. From about 4.1 to 3.8 billion years ago, failed planets and smaller asteroids slammed into larger worlds, scarring their surface. Near the end of the violence, during a period known as the Late Heavy Bombardment, impacts in the solar system may have increased. The increased activity most likely came from the movement of the giant planets, which sent debris raining down on the smaller rocky worlds.

Earth Core Formation

150 BCE

It is believed that core formation occurred when the Solar System was very young – less than 30 million years old. The Earth formed from a cloud of dust and gas, and material began to come together to form kilometer-sized planets known as “planetesimals”. These planetesimals rapidly joined together to form larger planets, thousands of kilometers in diameter. Researchers think that the Earth had already formed a core at this early stage

Generation of an Oxygen-rich Atmosphere & Appearance of Life

35 BCE

The first whiffs of oxygen — from the evolution of photosynthesis — emerged in rocks about 3.5 billion years ago

Formation of the Crust

30 BCE

The young Earth's first tectonic plates were much smaller. The Earth's new crust grew rapidly, with about 70 percent of the crust formed by 3 billion years ago, researchers think.