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# Water and Life

## Water is essential for most life processes, including photosynthesis, cellular respiration, and other chemical reactions that occur in organisms.

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A Perfect Planet
Teacher Contributed

## A Perfect Planet

### Student Exploration

#### A Time Ago In A Galaxy Real Close

How old is the Earth and how did it form? What a great question, but how do you figure something like that out? Scientists have worked on this question for about as long as there have been "scientists". For evidence, they look at the formation and distribution of different rocks on Earth comparing them to the composition of other planets in our solar system, as well as, our Moon, comets, and meteors (now they are beginning to look at other planetary systems too). This information is interpreted through mathematics and in the light of all known physical laws of the Universe, forming a reasonable scenario about how our Earth came to be. The theory has changed quite a bit overtime, and it continues to change. However the broad strokes of what happened are pretty solid. Watch the below video to find out about the broad strokes.

Now that you are familiar with the general story, read this to find out about some of the finer points that scientist are still working out.

### Extension Investigation

Use the resources below to answer the following questions:

1. Where did the matter to form the sun come from? What physical force caused gases to concentrate to a density sufficient for nuclear fusion to take place or, to put it another way, what caused "the Sun to light up"?? How old do scientists estimate the sun is?
2. How much of the matter in our solar system was not pulled into the sun? What happened to this matter?
3. What do scientists feel caused the Earth to become a molten mass? What in the distribution of heavy and light elements on and in the Earth makes scientists feel the Earth had to be molten at one point?
4. What do scientists see banded iron rock formations as evidence of? How does this evidence affect theories of how life on Earth developed?
5. What new research has led scientists to believe the Earth was drier when it formed than was previously thought?

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