The Earth is Remarkably Suited for Supporting Life

The Earth isn’t like any other planets we have discovered in the universe. It’s very difficult to analyze far away planets and our knowledge is still very limited, so we shouldn’t assume we will never find another planet like the Earth.

But there are many things that we do know about how unique Earth is for supporting life, as we know it.

There are many variables in the environments of planets, and many of them must be within a very narrow range to support the types of living things found on earth.

Just a few examples of the most familiar variables are: the size and age of the Earth, the speed of the Earth’s rotation on its axis, the elements that are present on Earth and the amounts of those elements, the size and age of the sun, the distance from Earth to the sun and the path and speed of Earth’s orbit around the sun. Each of these factors are critical for life on earth.

So what do we mean by life “as we know it?” It may be possible for life to exist in other forms, but we don’t know anything about what those forms might be. Consider some key variables like oxygen and carbon dioxide, for examples. Plants need carbon dioxide for their metabolism, and they release oxygen. Animals need oxygen and release carbon dioxide. We share our planet with plants, which provide not only food, but the oxygen that keeps us alive.

If a planet does not have sufficient amounts of oxygen or carbon dioxide, any life forms that exist there would have to be radically different from any forms of life we have seen. The biological and chemical processes would have to be very different. We don’t know if that’s possible, but we do know it would be unlike any of earth’s life forms. The same is true of each of the elements that are necessary for life on Earth.

There are many critical variables that life on Earth depends on, and more are still being discovered. Over 200 critical variables have been identified as of this writing.

The chances that all of these variables would be in the range necessary to support life at the same time one one planet is so extremely unlikely that some scientists think there is almost no chance that any other planets in the universe are like the Earth. The Earth is very uniquely suitable for life.

One of the reasons Earth is so unique is that there were some very rare events that occurred in Earth’s early history. One was a collision in space that reduced the amount of water on Earth to about 0.2% of the amount present when Earth was formed. Without that unique event, there would be 500 times as much water on Earth as there is now. Life could not survive on this “water planet”.

For a more complete list of the variables that are required for life on earth as we know it, see the Uniqueness of Earth.