The Strangest of Moons
Many planets have moons, and some of the larger planets have many moons. However, the Earth's Moon is the largest in the solar system, relative to the size of its host planet. It is nearly one third the size of the Earth, so big in fact that the Earth and Moon together can actually be considered to be a binary planetary system.
Many Planets Have Moons
Other moons in our solar system are tiny by comparison and because they are so small they have little bearing on their host planets. This is certainly not the case for the Earth, which would be entirely different in almost every way if it were not for its large companion Moon.
The part the Moon plays in making our Earth a perfect haven for life is huge. Some of its major contributions are listed below.A more detailed explanation is available in our book.
The Moon and Earth's Orbit
Way back at the beginning of the solar system, 4.6 billion years ago, the Earth was a semi-molten ball of minerals, metals and gas. It spun on its orbit extremely quickly, probably once every two hours or so! The Moon is so large and was originally so close to the Earth that its gravitational influence gradually slowed down the rate of spin of the Earth.
The Moon and Earth's Seasons
The Earth was and is a very unstable planet, with a complex core. Like other planets of the solar system, it would have undoubtedly 'fallen over' on its orbit, not once but many times during its history - like a spinning top running down. The Moon has prevented this from happening because of the way it orbits the Earth. It has also allowed the Earth to maintain a particular angle relative to the Sun. This has been critical because it means that all parts of the Earth in turn get an even warming from the Sun throughout the year. This in turn means the presence of liquid water, which has been crucial for life. The Earth's path around the Sun allows for an even heating and cooling of the planet. This could not happen if the Moon did not keep the Earth at the correct angle of inclination.
The Moon and Earth's Surface
Other inner planets of the solar system, such as Venus and Mars have a solid surface. Like the Earth they are or have been volcanic but Mars for example has only one huge volcano. Neither Venus or Mars have continents like those on Earth and neither has oceans. When the Moon came into existance it was made from material that came from close to the surface of the Earth. This broke up the Earth's surface. Because the Moon was so big and so close, it's gravitational pull prevented Earth's crust from becoming solid - keeping it moving about and inspiring a process known as plate tectonics. This has meant that the Earth has many volcanos, spread out around its surface. These volcanos have constantly errupted, bringing metals and minerals from the centre of the Earth up to its surface. These metals and minerals have been crucial for the development of life.
The Moon and Earth's Oceans
At the start of its relationship with the Earth the Moon was very much closer to us than it is now. Its gravity was so great that it created huge tides in the Earth's oceans. These kept things moving and mixing at a time when it was important to create the 'chemical soup' upon which developing life would depend. As time passed the Moon gradually moved further away. The tides became less powerful but were still present, as they are today. Their presence is part of what allowed life in the oceans to gradually migrate to the land.