Formation of the Earth and Moon

Formation of the Earth and Moon

This animation demonstrates how the Earth and the Moon were formed.

Geography

Keywords

Earth, Moon, formation of the Earth, formation of the Moon, Solar System, proto-Earth, Theia, planet, protoplanet, rocky planet, terrestrial planet, Earth globe, astronomy, astrophysics, geography, physics, physical

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Scenes

Formation of the proto-Earth

The formation of the Earth is related to the formation of the Solar System. The gases that form the Solar System gradually started shrinking. Increasingly more matter gathered in the centre while temperature was constantly increasing. The Sun formed from this condensed molecular cloud of dust. Due to rapid rotation, the rest of the cloud scattered and flattened into an orbiting protoplanetary disc around the Sun. The dust particles in the protoplanetary disc collided and stuck together due to electrostatic attraction, forming planetesimals. When they reached a size of about one kilometre, they collided due to mutual gravity, forming protoplanets, which were a few thousand kilometres in diameter. This is how the Earth was formed 4.6 billion years ago.

Around 170 million years after the formation of the Earth, a similarly young planet known as Theia struck the Earth’s still soft crust. Theia was demolished after the collision, and it merged with the Earth. The Earth’s mass therefore increased, effectively reaching its current mass. The impact created a large ring of debris around the Earth, which later formed into the Moon.

After the dissolution of the ring, the Moon became a glowing hot celestial body orbiting 25,000 kilometres above the Earth. During this period, the Moon still had volcanoes, lava flows and its own magnetic field.

The tidal phenomenon that occurs between the Earth and the Moon led to various changes. Firstly, the Moon became tidally locked with the Earth, meaning it takes the Moon just as long to rotate around its own axis as it does to revolve around the Earth. Secondly, the Moon gradually receded from the Earth, cooled down and then became geologically inactive.

Currently, the average distance of the Moon from the Earth is 384 thousand kilometres. Even to this day, it is receding from the Earth (3.8 cm a year). As a result, it takes the Moon increasingly more time to revolve around the Earth; however, due to tidal locking, the period it takes to rotate around its own axis is also increasing. The tidal phenomenon also affects the Earth; the Earth’s rotation period is decreasing, meaning the length of the Earth’s day is slowly increasing.

Definitions:

Planet: an astronomical object orbiting a star (e.g. the Sun) that is not massive enough to cause thermonuclear fusion (therefore it is not luminous), but massive enough to be rounded by its own gravity.

Star: a luminous sphere of plasma, shining due to the various fusion reactions that take place inside its core.

Solar System: the Sun dominates the Solar System gravitationally. The system is a sphere approximately 2 light-years in radius. Numerous small bodies orbit the centre of it, the Sun.

The Giant Impact

Formation of the Moon

Cooling down

The Earth and Moon today

Animation

Narration

The formation of the Earth is related to the formation of the Solar System. The gases that form the Solar System gradually started shrinking. Increasingly more matter gathered in the centre while temperature was constantly increasing. The Sun formed from this condensed molecular cloud of dust. Due to rapid rotation, the rest of the cloud scattered and flattened into an orbiting protoplanetary disc around the Sun. The dust particles in the protoplanetary disc collided and stuck together due to electrostatic attraction, forming planetesimals. When they reached a size of about one kilometre, they collided due to mutual gravity, forming protoplanets, which were a few thousand kilometres in diameter. This is how the Earth was formed 4.6 billion years ago.

Around 170 million years after the formation of the Earth, a similarly young planet known as Theia struck the Earth’s still soft crust. Theia was demolished after the collision, and it merged with the Earth. The Earth’s mass therefore increased, effectively reaching its current mass. The impact created a large ring of debris around the Earth, which later formed into the Moon.

After the dissolution of the ring, the Moon became a glowing hot celestial body orbiting 25,000 kilometres above the Earth. During this period, the Moon still had volcanoes, lava flows and its own magnetic field.

The tidal phenomenon that occurs between the Earth and the Moon led to various changes. Firstly, the Moon became tidally locked with the Earth, meaning it takes the Moon just as long to rotate around its own axis as it does to revolve around the Earth. Secondly, the Moon gradually receded from the Earth, cooled down and then became geologically inactive.

Currently, the average distance of the Moon from the Earth is 384 thousand kilometres. Even to this day, it is receding from the Earth (3.8 cm a year). As a result, it takes the Moon increasingly more time to revolve around the Earth; however, due to tidal locking, the period it takes to rotate around its own axis is also increasing. The tidal phenomenon also affects the Earth; the Earth’s rotation period is decreasing, meaning the length of the Earth’s day is slowly increasing.

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