Most people don’t know this scientific fact, but the Earth’s Moon is slowing moving further from the Earth. Each year its orbit around the earth experiences a mean recession rate of 2.16 cm/year (less than an inch, since approximately 2.5 cm = 1 inch).

What causes this? As the moon’s gravity pulls on the Earth, the Earth’s gravity pulls on the moon, making the Moon slightly egg-shaped. In addition, tidal friction, caused by the movement of the tidal bulge around the Earth, takes energy out of the Earth and puts it into the Moon’s orbit, making the Moon’s orbit bigger and slower. Thus, not only is the orbit of the moon getting bigger, it is slowing down. Another startling fact is that the Earth’s rotation is slowing down because of the energy lost to the Moon’s orbit.

How real is this effect? To answer this question, let us consider how the Earth’s Moon was formed. Most astrophysicists contend the Moon was formed when a  proto-planet (named Theia after a Greek goddess) about the size of Mars collided with the Earth around 4.5 billion years ago. After the collision, the debris left over from the impact coalesced to form the Moon. Initially, our newly formed Moon orbited the Earth at 22,500 km (14,000 miles) away, compared with 402,336 km (~250,000 miles)  today.

This theory, regarding the Moon’s formulation and gradual recession from the Earth, has been mathematically modeled. Computer simulations of such an impact are consistent with the Earth Moon system we currently observe. There is also physical evidence. Paleontological evidence  of tidal rhythmites, also known as tidally laminated sediments, confirms the above theory. 

What is this going to mean to us on Earth? The speed at which the Moon is moving away from Earth will eventually affect life on the planet, but it will take billions of years for the effect to become significant. Given that Archaic Homo sapiens, the forerunner of anatomically modern humans, evolved between 400,000 and 250,000 years ago, and our progress from cave dwellers to space adventurers during our existence on Earth, it is likely we will have colonized new Earths long before the Moon’s orbit threatens our existence.

There are numerous scholarly papers that delineate the mathematics and palentological evidence in detail. However, they all come to essentially the same conclusion. The Moon is moving further away from the Earth each year.