Alan Neves, Deseret News
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.
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