Venus is closer to the sun than the earth is. It has a very thick, dense atmosphere, made up mostly of carbon dioxide. The carbon dioxide acts like a blanket and keeps the sun's heat is trapped on the surface of Venus. This is called the Greenhouse Effect. Scientists tell us that the temperature on Venus is about 890 degrees Fahrenheit. This is 477 degrees Centigrade (or Celsius). At this temperature lead and tin would be melted. Carbon-based life forms would be vaporized. Water would boil away. It is difficult to discover what the surface of Venus is like. Our earth probes do not survive long in the heat, and the dense atmosphere makes it difficult to transmit information and signals.
Earth would be too cold for life if it had no atmosphere. The atmosphere holds enough of the sun's heat to make life possible here. Temperatures on earth range from a high of perhaps 130 degrees Fahrenheit to about -90 Fahrenheit. There are places on earth in which it is challenging for us to stay alive. For example, the temperature on earth in Los Angeles is about 70 degrees Fahrenheit, which is 21 degrees Centigrade. This is pleasant for carbon-based life forms, though some with adaptations for cold might feel uncomfortably warm.
Mars is the furthest rocky planet from the sun. It is a smaller planet than the earth, and has lost much of its atmosphere. The weaker gravity of Mars allows more atmospheric molecules to escape into space. As a result of Mars' very thin atmosphere, solar heat escapes easily. The temperature on Mars can be as high as 50 degrees Fahrenheit (10 C) at the equator and as low as -185 degrees Fahrenheit (-120 C) at the poles. Carbon-based life forms could survive at the warmer temperatures (given oxygen and other necessities) but the water in our cells freezes at 0 C, and maintaining our body heat would be challenging in even the warmest areas. We would have to really focus on staying warm at night and during the winters.
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