• The Moon has been present in the sky above since the earliest signs of life on Earth.
• Humanity has gazed up at it since our earliest days, striving to explore its surface and confirm it isn’t made of cheese.
• While the Moon is nearly 400,000 km away, life on Earth feels its impacts every day.

The most likely cause of the Moon’s formation is a major collision between two or more bodies during the earliest days of the solar system. The early Earth and another small planet, probably about the size of Mars, collided with such force that huge amounts of debris were thrown out from the proto-planet’s surface about 4.5 billion years ago. This was confirmed when the very first moon landings in the 1960s and 70s bought back hundreds of kilograms of rock for scientists to study. They found that the chemical composition of Earth and Moon rocks were very similar, suggesting a common origin, and that the Moon was molten during its formation.

The Earth’s tides

The Moon has had a long and complex impact on humanity’s culture, appearing in art, mythology, and religion across the world, and has been driving a new age of both robotic and human exploration as we enter the 2020s. However, its impact on the natural world has been felt since the earliest days of its orbit.

Perhaps the most well-known impact of the Moon is its role in the tides on Earth. The Earth and the Moon each exert a gravitational pull on the other. On the Earth, this causes the oceans to bulge outwards on the side closest to the Moon, and on the side furthest away from the Moon – this is where we would see a high tide. As the Moon orbits around the Earth, this bulge follows the Moon and so someone standing on a coastline will see the tide rise and then fall roughly twice a day.

The Moon has had a long and complex impact on humanity’s culture, appearing in art, mythology, and religion across the world.

The rise and fall of seawater levels is essential to the ecosystems that have evolved in these constantly changing habitats. The species that live in these intertidal zones depend on the alternation between flooding and exposure. Rocky shores, tidal flats, salt marshes and estuaries all support unique, interconnected species, such as wading birds, mud-dwelling organisms and marine life.

The Moon’s wobbles

The daily rise and fall of the tides is essential for life in these intertidal ecosystems, but the Moon also drives longer cycles in the natural world. During the 27 days it takes to rotate around the Earth, its angle changes slightly and it appears to wobble. Not only does the Moon change its tilt throughout each monthly orbit, the orbit itself changes. The Moon’s orbit is inclined very slightly compared to the Earth’s plane of rotation around the Sun, and this orbit slowly changes over 18.6 years. This means that a location on Earth will see a peak in tidal heights roughly once every 18 years.

Scientists have discovered that this 18.6-year cycle drives a natural cycle of growth and reduction in mangrove forests in Australia. Mangroves are dense groups of trees that live along shorelines and estuaries in the tropics and subtropics and flood twice a day with the rising tide. They are an extremely important for protecting coastlines and support a range of life, but they are also excellent at sequestering carbon and helping to prevent climate change. Being able to predict when mangroves are expanding by using the Moon’s orbital cycle means we can further promote their growth and restore these important ecosystems.

Ruth Kirk is a science writer based in the UK.