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Life on Earth would be much different without the moon. In fact, it’s safe to say that the large diversity of life we find on Earth wouldn’t exist at all. Without the stabilizing effects of the moon, life on Earth would exist only in small, compact niches. Life on Earth, without the moon, if it existed at all, would be confined to a narrow band along the equator. All the plants would be short, deeply rooted and ground-hugging. And any land animal would be short, squat and stout. Birds and any flying insects would be impossible.
Let’s begin with some moon basics. As most of us know, the tides are produced by the moon. The sun also creates tides, but because it’s so far away (93 million miles), its tide–producing effect is about a third that of the moon. The movements of the tides depend on two things: First, the gravitational attraction of the moon, and second, the centrifugal force of the moon-Earth orbit.
Bruce Parker, author of "The Power of the Seas," explains how it works: “Gravitational attraction pulls the earth and the moon toward each other, but at the same time centrifugal force pushes them apart because they are both revolving around a common point.” (The sun).
Giles Sparrow delineates it further in his book "Moon." Gravitational attraction and centrifugal force exactly balance at the center of the earth. On the earth’s surface, on the side closest to the moon, the gravitational force is greater than the centrifugal force (thus the water on the earth’s surface is pulled in that direction, giving that side of the world a high tide), and on the opposite side of the world the centrifugal force is greater than the gravitational force (thus the water on that side of the world will be pulled toward the center of the earth, producing a low tide on that side of the world).
The sun also contributes to the tides, Sparrow explains. When the sun lines up with a new or full moon, its gravity adds to the moon’s and causes an even larger tide. This is known as a spring tide. And during the first and third quarters of the moon, the sun’s gravity pulls in an opposing direction, which evens out the moon’s pull, creating a lower than normal tide, called a neap tide.
The moon plays a second major role on the earth and the life that exists upon it. Its gravitational pull stabilizes the tilt of the earth, and that produces more moderate climates and seasons. Earth’s equatorial plane is tilted at about 23.5 degrees in respect to the sun. It’s this tilt that gives Earth its seasons. But even with the stabilizing effect of the moon, the earth’s axial tilt still varies by about a degree over the course of hundreds of thousands of years.
Jason Barnes, an astronomer and assistant professor of physics at the University of Idaho, led a group of researchers who studied the effects of the moon’s gravity on Earth and how life on Earth would be different without it. Their research showed that without the moon’s gravitational influences, Earth’s axial tilt would vary by 10 degrees over hundreds of thousands of years.
“When the earth is tilted more, the seasons are more extreme,” Barnes said. “The summers are hotter and the winters are colder, and when the tilt is less, then the seasons are moderated, so the summers are cooler and the winters are warmer.”
This one degree tilt over hundreds of thousands of years is what caused the ice ages.
“That small tilt causes the seasons to be more extreme,” Barnes said, “which makes the summers hotter and the winters colder.” It was during this period of hotter summers and colder winters that the glaciers that used to cover North America and northern Siberia melted off, Barnes said.
“And when the seasons are less extreme,” Barnes said, “so when the summers are cooler and the winters are warmer, there’s more snow and less melted off, and that’s what causes the glaciers to form and the ice ages. So even that one degree tilt causes these huge shifts in the earth’s climate, into glaciated and non-glaciated states."
And without the moon’s stabilizing gravitational influence, the earth’s axial plane would vary by 10 degrees, Barnes said, which would have huge consequences for life on earth.
Ice ages could potentially be 10 times as bad as they have been. With climate shifts that dramatic, glaciers would cover the entire planet except for possibly a small band at the equator. Whatever life did exist would exist in a concentrated band at the equator.
But that’s just the beginning of the many ways that the moon stabilizes the earth’s climate. Without the moon, the earth’s days would be only six to eight hours long, explains Neil Comins in his book, "What if the Moon Didn't Exist?"
The moon was created about 4.5 billion years ago when a small planet traveling through space collided with the earth at 25,000 miles per hour. The collision sprayed more than 5 billion cubic miles of the earth’s outer layers into space. This material eventually gravitated into the moon.
As mentioned above, the earth would still have tides caused by the sun, but they’d be about a third the size as they are today. And the moon’s larger tides, over millions of years, have slowed down the earth’s rotation, says Comins.
“The motion of the water pushing against the continent and the friction generated by that water rubbing against the ocean bottom would both act to slow down the earth’s rotation,” he wrote.
Scientists estimate that without the tides, the earth would spin about three to four times faster than it does. And that would have big implications on its life forms. First, winds on earth would be so fast and powerful that few things could grow.
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Winds are generated by a planet’s rotation and the cooling and heating of its air. For example, Comins said, “Jupiter and Saturn have 10-hour days. They rotate so rapidly that the friction between their surfaces and atmospheres pulls the air into narrow, streaming belts of wind.” They have winds up to 300 miles an hour. They have hurricanes that last for years and even centuries. Earth, without the stabilizing effects of its moon, would be the same. If plants did exist, they would be short, deeply rooted and ground-hugging.
And any land animals that existed on such a planet would be all short, squat and stout. Birds and any flying insects would be impossible.
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