How the Earth started and it's first one billion years of history
The Earth started forming about 4.6 billion years ago with accretion. Accretion is the accumulation of particles into a massive object by gravitationally attracting more matter. Earth started out as a small object and exponentially attracted more matter until it got the size that it is today.
The Outer core of Earth is a fluid layer of Earth about 1,400 miles thick. It is between the mantle and the inner core. As the Earth was cooling, heavier elements went to the center of Earth.
The most accepted hypothesis for how the moon formed is the giant-impact hypothesis, which suggests a planetary body the size of Mars collided with earth, and the debris from the collision combined to create the moon. The moon was formed approximately 4.5 billion years ago.
Planetary cooling is when the planet's molten lava starts to cool to form the planets crust. The faster the planet cools, the thicker the crust will be. The Earth cooled slowly, so the crust is thing compared to other planetary objects. The Earth started cooling approximately 4.1 billion years ago.
Late Heavy Bombardment was an event that occurred early in Earth's history, but after the Earth had created most of its mass. It was a time period where an abnormally large amount of asteroid hit the Earth and other planets It ended approximately 4.1 to 3.8 billion years ago.