Day 35.

We began yesterday contemplating the fragility of the planet we inhabit. Here are some more facts: What about the earth’s spin? If it were slower our nights would be too long and then it would be too cold for vegetation and everything would freeze overnight. The days would be too hot and would dry out even the largest forests. If it were to spin faster the earth would become shorter and fatter (and look like a pumpkin). As you traveled toward the equator your weight would diminish, you would be able to jump higher and you would have to adjust to shorter nights and days. You would have to sleep 4 hours, rush around and do all your work in a few short hours of light.

What about the tilt of the earth? At present our earth is tilted on an axis of 23.5 degrees. This produces the seasons as the earth revolves around the sun. If there were no tilt, there would be no seasons. If the tilt were increased the seasons would be more severe, the equator would become an endless burning summer and most of the earth would be an endless night of winter. The changes would be unendurable, they would produce violent storms and life could exist nowhere except in a strip 1300 kilometres wide around the equator.

What about the moon? If the moon were further away our tides would become smaller and they wouldn’t wash the coast and the coast would become stagnant and choked. We’d get the same effect if the moon were smaller. But if the moon were closer, or larger, the tides would be so large that they would sweep over the continents, eroding the mountains and destroying the world. But the moon is serene and secure in space at the end of the gravitational tether where somebody put it. It reflects the sunlight, it keeps track of time at quarterly intervals and is a spectacular example of celestial engineering.

The earth is protected by a donut shaped magnetic shield, called the magnetosphere. These are invisible lines of force that catch marauding electrons from the sun, slows them down to about the speed of sound and re-routes them southward or northward and funnels them down, harmlessly, around the poles in a display called the Aurora.

Earth’s protective atmosphere is the same. The upper level is 1600 kilometres above the earth. About 450 kilometres up is the ionosphere, filtering out a deadly cocktail of death rays (ultraviolets, x rays, gamma rays and cosmic rays) some traveling almost at the speed of light. This ionosphere, however, lets the beneficial rays through. It also burns up the meteors.

If our atmosphere was thinner, it would let most of the meteors through. If it were thicker we wouldn’t be able to bear the weight. Imagine going for a walk in the open with meteors crashing all around and what kind of houses would we have to build? Strangely this ionosphere lets through those ultraviolets we need. For example the long ones for plant life and the ones that kill bacteria and the ones that help manufacture Vitamin D in the human skin. Who invented this screening process for meteors and the sun’s rays?