Quote:
Originally Posted by Nereidalbel
If not on Europa, the original Star Trek series may have had it right with silicon-based life in an anoxic environment.
|
Silicon doesn't look like a good replacement for carbon for making life. It just can't easily form the long polymers that carbon can, so you don't get analogues of DNA, RNA, proteins, or fatty acids.
Quote:
Originally Posted by Nereidalbel
What doomed Venus was the lack of a carbon cycle more than anything. On Earth, plate tectonics ensure that carbon is cycled through the mantle regardless of life, while Venus only experiences any sort of recycling in massive events every few hundred million years. Accelerate Venus' rotation enough to weaken the crust, and it may actually be habitable.
|
This sounds like a chicken-and-egg problem. Consider the following scenario, starting with a Venus with a full plate tectonics cycle and an atmosphere consisting primarily of nitrogen at about 1 Earth atmosphere of pressure :
* The increased insolation of Venus results in two effects - (1) more water evaporates so there is more water in the atmosphere, and (2) the water can rise higher in the atmosphere before it condenses and rains out.
* Water is a strong greenhouse gas, so the thicker blanket of water results in even higher temperatures, which leads to more water and thicker blankes of water due to its higher altitude, leading to even more water in the air and even higher altitudes before condensation.
* The water rises high enough in the atmosphere that significant ultraviolet light can get through and hit the water. The water is photodissociated into hydrogen atoms and hydroxyl radicals. The hydrogen escapes into space (Jeans escape), and over time the water starts to dissapear leaving an atmosphere enriched in oxygen behind.
* While this is happening, surface temperatures get high enough to bake carbon dioxide out of lime deposits. Now the carbon dioxide acts as a greenhouse gas as well, accelerating the process.
* Oxygen reacts with minerals in the venerian crust, and is removed from the air.
* Water is a major lubricant for plate tectonics here on Earth. As water is removed from the air, it gets harder for the plates to move around and eventually the tectonic cycle grinds to a halt.
* The water is eventually fully photolyzed and drifts away. This leaves a world with a thick atmosphere of carbon dioxide and no plate tectonics.
Luke