q: Was Earth always solid? a: no q: Why not? a: extreme volcanism q: Any other reason? a: collisions with other bodies. q: Did the collisions occur frequently? a: fno q: What formed on the outside? a: a solid crust q: Did the Moon form before or after the crust? a: after q: What became plentiful in the atmosphere? a: water q: What caused the Moon to be created? a: The Earth was hit by an object q: What size object? a: the size of Mars q: Did some of the object stay on Earth? a: yes q: Where did the rest go? a: into space q: What are the seas made of? a: water vapor q: Anything else? a: comet ice q: How many things created the atmosphere? a: two q: What was one? a: Outgassing q: And the other? a: volcanic activity q: How big was the object that hit the Earth? c: Earth was initially molten due to extreme volcanism and frequent collisions with other bodies. Eventually, the outer layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards, possibly as the result of a Mars-sized object with about 10% of the Earth's mass impacting the planet in a glancing blow. Some of this object's mass merged with the Earth, significantly altering its internal composition, and a portion was ejected into space. Some of the material survived to form an orbiting moon. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans. 

Earth was initially molten due to extreme volcanism and frequent collisions with other bodies. Eventually, the outer layer of the planet cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards, possibly as the result of a Mars-sized object with about 10% of the Earth's mass impacting the planet in a glancing blow. Some of this object's mass merged with the Earth, significantly altering its internal composition, and a portion was ejected into space. Some of the material survived to form an orbiting moon. Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered from comets, produced the oceans.
10% of the Earth's mass