The moon's gravitational pull (along with the gravitational pull of the sun, of course) has shaped much of Earth's past and present. The moon impacts the Earth's tidal patterns, but tides are one of the more observable results of the moon's gravitational pull. What about the less obvious influences that the moon’s gravity has on our planet?
A 2015 botanical study suggests that the moon's gravity might affect the movement of some plants' leaves. After studying historical plant data as well as data from vegetation grown on the International Space Station, researcher Peter Barlow concluded that there could be a correlation between movement of water within the plant’s leaves and the lunisolar tide cycles, in a movement referred to as "leaftide." Further studies are needed to get more insight into the relationship between lunar gravitational pull and botany and perhaps reveal other influences of the moon’s gravity on flora — and perhaps beyond.
While the relationship between leaf behavior and the gravitational pull of the moon remains uncertain, scientists have discovered some interesting connections between the moon’s gravitational pull and aspects of life on Earth.
Slightly longer days
The moon's gravitational pull slows down the Earth’s rotation, in a phenomenon known as "tidal braking" at a rate of 2.3 milliseconds each century, so — in theory — a sunny day in 2115 will be 2.3 milliseconds longer than today. Going back 1.4 billion years ago, a day was roughly only 18 hours because the moon was closer to Earth, according to a 2018 study.
This isn't a huge problem for the next few generations of calendar makers, but when you look at things from a million-to-billion-year-perspective, it might matter. However, some scientists believe that the 2.3-millisecond-per-century rate is not consistent because of ongoing changes in the Earth's oceans and continents over time.
Earth's axis, the seasons and life on our planet
We have the moon's gravity to thank for the Earth's steady axis and it's one factor among several that influence Earth's consistent rotation in the same direction. Earth's unique and favorable axis of rotation determines the seasons and keeps our climate amenable to the development of life. Our moon also stabilizes Earth on its axis, so it's less wobbly than it would be otherwise.
What about the influence of Earth's gravitational pull on the moon?
It's a two-way street where gravity is concerned. Not only is the Earth's gravitational pull responsible for the moon's egg shape, having pulled on a young moon during its formation, but it is also still causing the moon's shape to change. The Earth causes "lunar body tide," which creates "bulges" on the surface of the moon, one on the Earth-facing side, and a matching lump on the far side.
So, not only does the moon light our night skies, inspire wonderment and dictate the schedules of werewolves, it also makes life as we know it possible. From its influences on the tides to the regulation of the seasons, we have many reasons to thank our celestial neighbor. To deprive the moon of due credit would be sheer lunacy.
Editor's note: This article has been updated since it was originally published in September 2015.