Dr. Fred Ask Dr. Fred


by Dr. Fred Bortz

Safesurf Rated All Ages

For more than twenty years, Dr. Fred Bortz worked as a scientist, researcher, and teacher. Now he spends most of his time writing books and articles for young readers like you.

He enjoys both science and writing for the same reason: HE LOVES QUESTIONS. He writes for people your age because he knows you love questions, too.

To find hot-links to other "Ask Dr. Fred" questions and learn how to send Dr. Fred your favorite question, go to the main "Ask Dr. Fred" page.

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"What if the Earth Had No Moon?"

This question has been sent frequently by many young readers. I've decided to make it a featured question on the "Ask Dr. Fred" pages.

Dear Moon-watchers,

Compared to the moons of other planets, Earth's Moon is an unusually large object. If you imagine placing an ordinary planet and one of its moons on a balance beam as long as the distance between them, the planet is so much more massive than its moon that the center of mass, or balance point, would be very close to the center of the planet. That is not true for our planet and its moon. In the Earth-Moon system, the center of mass is barely one quarter of the way inward from surface of Earth toward its center. Only Charon, the moon of tiny, icy Pluto, creates a balance point farther out from the planetary center. The center of mass of that pair is actually outside Pluto in empty space. Thus many scientists consider Pluto-Charon a double planet system.

You probably know that the Moon's gravity creates tides on Earth by attracting the water of the ocean. It actually creates two high tides daily, one on the side of Earth closest to the Moon, and one directly opposite. You can think about that happening because the ocean bulges outward in both directions when the Earth-Moon system spins around its balance point. If the balance point was almost at the center of the Earth, the bulge would be nearly the same all around and the tide would not vary much during the day.

The movements of the tide have always created special environments on Earth. Many life forms have developed in these tidal pools and basins. Without tides, the kinds of plants and animals on Earth would be quite different than those we know today. So we can safely say that life forms would have been different at all times of Earth's history. If Earth didn't have such a large satellite, it wouldn't have had dinosaurs in the Mesozoic Era, and it wouldn't have people today.

In fact, no complex life of any kind would have ever emerged. The evolution of complex life forms requires long periods of stable conditions. Without the Moon, the Earth's axis (the imaginary line through the North and South Poles) would wobble like a top that has been hit by a misbehaving child, or like a tightrope walker without a balancing pole. With the Moon, the axis wobbles a little bit but generally stays put. That keeps the seasons more or less the same for periods long enough for complex life forms to develop, adapt, and succeed.

The Moon is good for a whole lot more than simply lighting up the night sky. If you wonder what your life would be like without it, the surprising answer is that you wouldn't be here to wonder at all!

I hope you always follow your questions!

Scientifically yours,
Dr. Fred

You have just read the most popular "Ask Dr. Fred" question. Don't you want to learn more?

Click here for "Is there life on Mars?", "What Killed the Dinosaurs?", "Is Pluto a Planet?", "Good and Bad Ozone", "Why is the sky blue?" and more!

You can read about how the Moon formed in a great collision between Earth and another planet in Dr. Fred's book Collision Course! Cosmic Impacts and Life on Earth
Text copyright 2000-2003 by Alfred B. Bortz, all rights reserved

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