The Grand Project: An Introduction
your choices into the next article, so don't wait until the last minute to answer.
Look to the Sky
One of the most important things to decide is what kind of atmosphere your planet has. This will quite literally determine the type of life it's capable of supporting. I'm going to stick to an Earth-like atmosphere for ours since this project is not focused specifically for science fiction writers. This atmosphere changes over time, of course, but today our atmosphere contains 79% nitrogen, 20% oxygen, and 1% other gasses.
The atmosphere is also in a number of layers. Air from these layers does not mix. We Earth-bound creatures only deal with the troposphere as a general rule, which extends around nine miles above the surface. The tallest mountain on Earth is Mt. Everest, and it's only around five and a half miles high. When you fly in a jumbo jet you might only be seven and a half miles up. This leaves you still in the first layer.
On top of this is the stratosphere. Among other things, the ozone layer lives here, toward the top of the layer. You've probably heard over and over with all of the controversy about holes in the ozone that this is where much of the ultraviolet (UV) light from the sun gets absorbed. There are three bands of UV light, predictably named UV-A, UV-B, and UV-C. UV-A is not absorbed by the ozone but is the lightweight of the bunch. It contributes to skin aging and wrinkles and is why your outdoor paint and plastics fade over time. It also contributes toward what tans and sunburns you get. UV-B is the nasty one. It is partially absorbed by the ozone layer and is what most of the hole in the ozone fuss is about. This segment of ultraviolet light causes skin cancer (it's the major contributor for sunburns), cataracts, and DNA damage in many living things. The nastiest is UV-C, but it never gets past the ozone layer and the oxygen in the troposphere, though some might add "yet." The temperature in this layer is from around -40C to -74C.
Around the stratosphere is the mesosphere. We've gone past the bounds of ozone and water vapors now. It's almost -100C by this point because little heat reflecting from the Earth's surface reaches this high. Anything coming from space like an asteroid or meteor begins to heat up when it
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