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Name: Megan
Status: student
Grade: K-3
Location: MA
Country: N/A
Date: 9/28/2005
Question:
Why is the earth the only planet that things can live on?

Replies:
We do not know the answer to this question -- one way or the other. Earthlings have not identified such planets, which may be less "advanced" than Earth, "equivalent" to Earth in technological capabilities, or "far more advanced" than our global culture. It is not even a "given" that their evolution (I know that is an inflammatory word.) has developed along the lines of carbon based chemistry as has life on Earth. It may be better, or worse. We also have to realize that our ability to 'communicate' with any such hypothetical life has a narrow time "window" given the finite speed of light and our technological capabilities that are only about 100 years old. So, without any prejudice, we just do not, cannot know if there is another astronomical body that harbors life, or life'like' organisms.

Vince Calder

Megan,

There are many reasons why the Earth is "just right" for life.

If a planet is too close to the Sun, it will be too hot to support life as we know it. If the planet is too far from the Sun, then it will be too cold - water, which we know is important to the kind of life we are used to seeing will be ice, and that is not useable for life.

Also, how much mass (how heavy) the planet is also has an effect on how much air the planet can hold onto. If the planet's gravity is too weak the air escapes into space.

Also, the fact that the Earth has a moving molten iron core provides a magnetic field which shields life from the more harmful radiation from the Sun.

But, having said all that, we have to be careful and say that Earth is just right for the kind of life that we know - as we know life to be. There may be other planets that can support life, but it may be a kind of living thing that is very different from what we see on Earth.

Greg (Roberto Gregorious)


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