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Forces of the Wild
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Recipe for Life

It's hard to imagine that our precise and orderly solar system was formed out of the cauldron of gases and dust that once swirled through space. It's even harder to imagine that life, in all its wondrous shapes and sizes, emerged from the same morass. Yet miraculously, it did. Why? Because the recipe on Earth was just right. As you see in the NATURE mini-series FORCES OF THE WILD, the newly-formed Earth went through a lot of changes before conditions could allow life to begin.

Many forces have helped to shape our planet.
When the solar system came into existence about 4.6 billion years ago, the Earth was just a lump of rock. Over time, as some of its radioactive rocks began to decay, the Earth heated up tremendously. It rearranged itself in new layers, developing a cooler outer crust. Gases escaped from inside the planet and formed a new atmosphere of nitrogen, carbon dioxide, ammonia, methane, and water. The methane and carbon dioxide, both "greenhouse gasses," helped to retain some solar warmth around the planet as it continued to cool. Finally, about 3.8 billion years ago, water vapor condensed from the atmosphere and formed the oceans. Water in liquid form was crucial for the start of life, and most scientists believe that life arose soon after the oceans formed.

First, non-living amino acids, the "building blocks" from which life was constructed, spontaneously arose out of the surfaceís chemical soup, probably stimulated by energy sources such as electrical discharges or ultraviolet radiation. Next, according to one theory, those elements combined to form more complex materials when they concentrated around charged minerals at the site of submarine vents.

In the next step on the road to life, those materials formed "microspheres," with structures similar to cell walls. However, they still were not alive: two more steps were needed.

First, the microspheres had to develop enzymes that would push along even more chemical reactions. And most importantly, they had to develop a simple genetic system: the chemical DNA. Once that was done, these chemical conglomerations, now called prokaryotic cells, were considered to be alive: they could reproduce themselves. From those primitive cells evolved all the forms of life we see today, from simple bacteria to enormous elephants and, of course, human beings.

Why didn't these events happen on any of the other planets in our solar system? They just didn't have the right conditions.

Planets farther out in the solar system, such as Neptune and Pluto, are so far from the sun that they have little warmth, and the essential chemical reactions cannot take place at temperatures as low as -373° F. On the other hand, Mercury and Venus have temperatures so high -- up to 848° F -- that any compounds that might form would not be able to survive. On Earth, the temperature just happened to be right. In addition, the Earth is just the right size and density (not tiny like Pluto, not enormous like Jupiter).

It is large enough to have sufficient gravitational pull to hold an atmosphere, yet the atmosphere is not so dense that no sunlight can reach its surface. The Earth, it seems, is simply right for life.

Life, however, is not always happy with the Earth. At least, human life is not. Modern humans spend untold energy trying to control the Earth's natural forces. But as we see in FORCES OF THE WILD, no matter how hard we try, things like volcanoes, earthquakes, and the weather always seem to have the upper hand.

Recipe for Life
Why did life evolve on Earth?
Volcanic Action
The secrets of erupting volcanoes.
The Equinox
Why aren't our days and nights of equal length?
Understanding El Niño
What is El Niño?
Avoiding Destruction
Meet an earthquake hunter.
Volcanic eruption
Significant events in geological history.
For Teachers
View FORCES OF THE WILD lesson plans.
A bird
Web links and books related to the program.

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