Life and Evolution without the Moon

From controlling the tides to stabilizing global climates, evolution without the Moon would have taken a very different path.

Most scientists agree that the Moon formed around 4.5 billion years ago when the Earth was very young. The early solar system was a chaotic place where leftover protoplanets and asteroids hurtled into one another following the formation of the planets. When a Mars-sized object crashed into the primordial Earth, it practically ripped the planet in two, creating the Moon in the process. However, out of this fiery magmatic hell appeared the foundations for life’s evolution.

Night and Day

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If the formation of the Moon hadn’t boosted Earth’s rotational speed, a single day might last months!

One only needs to look at Venus to see a planet that could be much more like ours, at least if it had a moon of its own. However, a day on our so-called sister planet lasts almost 117 Earth days. Fortunately for us, the impact event that created the Moon exerted enough force that it sent the globe spinning around at a much faster rate than it perhaps otherwise would. In fact, the day may have been as short as six hours immediately after the Moon’s formation.

Earth’s rotational cycle has been getting longer ever since the Moon was born. In fact, scientists saw fit to add an entire extra second to the 24-hour clock on June 30, 2012. This might not sound like much but, at the time of the dinosaurs, the day was as much as an hour shorter than it is now. When the first known microorganisms evolved, some 3.8 billion years ago, the day was under nine hours long.

Although the Moon’s formation greatly accelerated the Earth’s rotation in the first place, it has been responsible for decreasing it ever since. The tidal drag exerted by the Moon, and the fact that it’s constantly moving away from us at a rate of 1.5 inches (4 cm) per year, continues to make the day longer. These tiny numbers might not sound like much but, over the course of the 3.8 billion years that life has existed on Earth, they get a lot bigger.

Rotational periods dramatically lower than they have been for the last billion years or so have a profound effect on Earth’s climate. Aside from a faster rotation translating into briefer days and nights, it also increases wind speeds thanks to the greater inertial forces involved. However, even more important, at least in the context of life and evolution, is the fact that the length of the day is ultimately responsible for the circadian rhythms that dictate the daily cycles of many living things.

The Tides of Evolution

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Tidal flats presented an environment where amphibious animals could migrate from the sea to the land.

With a rotational cycle unbounded by the formation of the Moon, the Earth would be as alien as a tidally locked planet orbiting a red dwarf star. That doesn’t necessarily preclude the possibility of life arising, but it would profoundly change the course of evolution. In other words, life on such a planet would be very different to that on Earth. Thanks to our lunar neighbour, however, we’ve had a guiding force determining the path of evolution since the very beginning. This force is largely defined by the gravitational pull of the Moon – the tides.

There is no doubt that the tides have always played an important role in evolution, perhaps most notably with the migration of life from the sea to the land some 430 million years ago. After all, tidal flats ultimately created an environment where amphibious and, ultimately, fully terrestrial, organisms could evolve. Even long before these times, however, the tides may have also helped facilitate the chemical reactions required for life to arise in the first place.

Since the tidal influences were much stronger when life first evolved on Earth and the Moon was much closer, high tides would have extended many miles inland at a much more frequent rate too. Research suggests that this environment led to faster tidal flooding and drying cycles which, in turn, increased salinity and helped jumpstart the formation of nucleic acids. These nucleic acids are DNA and RNA, the very building blocks of absolutely all life on Earth that has ever existed.

Seasons of Change

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Without the Moon to regulate Earth’s axial tilt, the seasons would be thrown into chaos, and organisms that rely on them would be unable to evolve.

Imagine a world without seasons. Hibernating animals wouldn’t exist, and deciduous plants could never evolve. It would be a very different place. However, while the Moon is not responsible for the seasons, it has an important stabilizing effect on the Earth’s axial tilt. It’s the fact that our planet is tilted some 23.44° that we enjoy seasons; without this tilt, there wouldn’t be any seasons at all.

The gravitational pull of the Moon limits the degree of wobble in the axial tilt. Even a small change could lead to mass extinctions due to the knock-on effect it would have on climates around the world. However, without the Moon to stabilize our seasons, the planet’s axial tilt could change unfettered, perhaps to such an extent that Earth could even end up rolling on its side! If that happened, the planet would end up with one hemisphere in darkness and the other in daylight for half a year.

One only needs to look at Mars to see what seasons are like without a large Moon to keep things under control. Although the Red Planet currently has an axial tilt od 25°, which is not much more than Earth’s, it can fluctuate between 13 and 40 degrees over just a few dozen million years. That’s more than enough to wreak havoc in any advanced ecosystems. Earth, by comparison, only fluctuates in cycles of between 22 and 25 degrees. Nonetheless, even these apparently small changes can cause major changes to Earth’s climate, ultimately shaping the course of evolution and extinction.

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We have a lot to thank the Moon for, dead and barren though it might be. Without it, life on Earth would be immeasurably different to what we know today. In fact, it might not have even arisen at all. What do you think the world would be like without our nearest neighbour? Let me know in the comments below!

Further Reading