THE EARTH Was it “Founded” by Chance?

THE EARTH
Was it “Founded”
by Chance?

TO AVOID extremes of temperature, the earth must orbit at the correct distance from the sun. In other solar systems, planets have been detected that orbit sunlike stars and are considered to be in the 'habitable zone'—that is, they are capable of sustaining liquid water. But even these so-called habitable planets may still not be suitable for human life. They must also rotate at the right speed and be the right size.

If the earth were slightly smaller and lighter than it is, the force of gravity would be weaker and much of the earth's precious atmosphere would have escaped into space. This can be seen in the case of the moon and the two planets Mercury and Mars. Being smaller and weighing less than the earth, they have little or no atmosphere. But what if the earth were slightly bigger and heavier than it is?

Then the earth's gravitation would be stronger, and light gases, such as hydrogen and helium, would take longer to escape from the atmosphere. "More importantly," explains the science textbook Environment of Life, "the delicate balance between the gases of the atmosphere would be upset."

Or consider just oxygen, which fuels combustion. If its level were to increase by 1 percent, forest fires would break out more frequently. On the other hand, if the greenhouse gas carbon dioxide kept increasing, we would suffer the consequences of an overheated earth.