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Why isn't Venus livable if it's just like Earth?
Answer 1:

Good question! Venus is much like Earth in some ways, but in other ways it is very different. The size and density of Venus is very similar to Earth, but its atmosphere is very different. The atmosphere is the layer of gas surrounding the surface of a planet, and it is very important in the livability of a planet because most life (on Earth) is at or very near to the surface.

Venus’ atmosphere is mostly composed of carbon dioxide. It is very dense (about 90 times the pressure of Earth’s atmosphere) and very hot (about 500 Centigrade) because of an extreme “greenhouse effect” from the carbon dioxide (Hamblin & Christiansen, 2004). Obviously, it would be impossible for a human to live there– we would be cooked by the heat and crushed by the pressure, but what about other life?

Life on Earth can live in extreme environments, like the freezing cold desserts of Antarctica and the boiling hot pools in Yellowstone. Organisms that live in these types of environments are known as “extremophiles”. Could an extremophile live on the surface of Venus? Life (as scientists understand it) requires at least two main things: 1) liquid water for chemical reactions to happen in and 2) a source of energy. Humans drink water to “hydrate” our cells and get energy by eating carbon and combining it with the oxygen that we breathe, but there are other ways to get energy as well. Some organisms get all of their energy from “chemical reactions” that take place in their environment. For example, the bacteria that live in hot, acidic pools in Yellowstone take advantage of the combination of sulfur and oxygen in the pools. There may be the potential for the first requirement on Venus. For example, an organism with a similar “metabolic pathway” as plants might be able to get their energy from the carbon dioxide and sunlight on Venus (although not much sunlight makes it through the dense atmosphere). Liquid water is the requirement that Venus probably does not fill. Scientists think that there may have been liquid water on Venus’ surface in the past, but not any longer.

Reference: Hamblin, W.K. & Christiansen, E.H. (2004). Earth’s Dynamic Systems. New Jersey: Prentice-Hall.

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