Why is Venus so different from Earth? Given their similar size, I would have thought they would be similar (a staple of early science fiction), but we’ve found out that Venus is hellishly hot with a primarily CO2 atmosphere.
How come? how did we lose out on having a sister planet? could Venus have ever have supported life?
Venus is just a bit too close to the Sun. It became too warm, and the greenhouse effect became what’s called a “runaway greenhouse”. When an Earthlike planet warms up, the process tends to feed on itself; evaporating water is another greenhouse gas, methane is released which is yet another, snow and ice vanish and the world absorbs more heat and so on.
On Earth, when the world becomes warm enough, eventually the warming becomes self limiting; for example, evaporating water becomes clouds which reflect sunlight, creating cooling. But when too much heat is coming in from the Sun and the world warms too far, the limiting factors are no longer strong enough and the world becomes warmer and warmer. The seas boil away, and then ultraviolet light from the Sun cracks the water vapor into oxygen and hydrogen. Then the hydrogen drifts off into space, and eventually you have a dry hot world like Venus. Barring human intervention this will also be the eventual fate of Earth, since the Sun is slowly warming over it’s lifetime.
As for life, it’s quite possible as far as I know; it probably didn’t have time to develop far before being fried though. For a “sister planet”, we’d probably have been better off if Mars and Venus had been swapped; a bigger Mars might have been able to hold onto enough air and water for life.
Funny thing, there… Mars is big enough to hold onto enough air and water for life. But for some reason, it didn’t. Both Earth and Mars have much thinner atmospheres than would be expected given their sizes and temperatures. Last I heard, the best guess is that Earth lost most of its atmosphere in the collision which formed the Moon, and Mars’ was eroded away by the solar wind due to its pathetically small magnetic field.
Incidentally, related to Earth’s thin atmosphere, it couldn’t go as bad as Venus. Even if we were as close to the Sun as Venus, and even if we did get a runaway greenhouse effect going, it couldn’t go nearly as far as it did on Venus, because there just isn’t enough carbon or other volatiles on the planet. Which is not to say that it wouldn’t be bad for us, of course.
Much of Earth’s presumably reducing primordial hydrocarbon atmosphere is also now locked away in organic compounds, largely in the form of living structures and residue thereof. Venus also lacks a strong magnetic field which doesn’t provide protection against the highly ionized solar wind that tends to leach away atmospheric hydrogen.
Making broad generalizations about the resulting differences between planets tends to gloss over the fact that minor changes in the history of a planet can result in dramatic diversions in planetary development. There are a number of reasons why Earth is so hospitable to modern life while we can’t imagine any type of organic life that could survive in Venus’ sulfurous environs, and reducing it down to one or two will probably miss important impact of other parameters.
Stranger
What about earthly extremophiles such as sulfur reducing bacteria? Too hot or not enough water?
Even extremophiles could not live in the pressure, temperature, and acidity of Venus’ atmosphere. Which is not to say that some kind of self-organizing criticality can’t live there, but it wouldn’t be anything like life as we know it.
Stranger
Would it be fair to say Venus is a BIT too close to the Sun, Mars a bit TOO far and Earth just right? Or is that completely off base?
Close; it’s sometimes called “the Goldilocks effect”. Although to be more precise, Venus is easily too close ( now ); Earth WAS just right but is now nearing too close ( due to the warming Sun ), and Mars is “just a bit TOO far”. Over time the zones move outwards as the Sun warms.
My understanding is the Earth has almost as much carbon as Venus, perhaps enough to give it 70 - 80 atmospheres of pressure if all of it were in the form of CO[sub]2[/sub]. (Venus has about 90 atmospheres of pressure.) Most of it is tied up but not in the biosphere or fossil fuels. Rather it’s in the form of calcium carbonate in rocks. And most of that got there via the calcium in the early oceans reacting with dissolved carbon dioxide.
It takes a considerable amount of heat to release the carbon from calcium carbonate. The Earth would basically already have to be in runaway greenhouse effect before most of it would be released.
This one of my pet peeve’s about the whole “greenhouse thing”. Some/many folks are under the impression that global warming could turn the whole earth into a sahara/venus.
worst case is a higher seas, slightly warmer temps, some places not so great to live in, and some other more places actually better to live in than currently.
If all humans lived and worked in mobile homes, global warming wouldnt even be a big deal IMO. But even if it is, Earth aint going Venus anytime soon.
To me the bigger danger is runaway ice age, which apparently has happened at least once in the earth’s past, with the whole of the earths suface being covered in ALOT of ice. Even a normal ice age renders a decent fraction of the earths surface unusable.
It was my understanding, that if all the glaciers were to melt, fresh water could be real hard to come by. This could be a real problem for farming. Maybe we will get lucky and Alaska will come through in fertile land. I don’t know what the worst case scenario is, but neither do you. Certainly higher seas and balmy winters isn’t the fear.
People need to eat, you know. Massive crop failures mean famine, regardless of people’s ability to move. And then there’s the problem of infrastructure; you wouldn’t just need mobile homes, but mobile factories, mobile power plants, an entire mobile electrical grid, and so on. You can’t make all of civilization mobile.
Except that as I’ve said, the Sun has gotten warmer; the time for a runaway ice age was in the ancient past, not now. Not that we seem to be in for a runaway greenhouse anytime soon in human terms.
Due to the Sun, or due to CO2?
In this 10 yo article 2 researchers from the University of Colorado at Boulder say that volcanos are responsible for the present climate on Venus: New Climate Modeling Of Venus May Hold Clues To Earth’s Future
I don’t know how widely accepted it is, but there’s a theory that the problem with Venus is that it doesn’t have any plate tectonics. Because of this, Venus can’t vent heat that builds up the way that the Earth does. The interior of Venus gets hotter and hotter and hotter until the crust finally melts. Then, once the heat has been vented to space, the surface cools, and the process starts all over again. I believe the main evidence for this is the fact that there aren’t enough craters on Venus, indicating that its entire surface is relatively young.
It depends. If the earth gets warm and dry, we’re all screwed. However, in the past, the earth was warm and wet. The entire area from about Florida to New York (latitude-wise, the lands have moved since then) was all roughly uniform in temperature, which is obviously not true now. The earth was covered in lush vegetation, and there were plants and trees all the way to the poles. Obviously, the entire way that the climate worked was much different than it is now. If the earth returned to this state, the frozen tundra would become fertile farmland, and the U.S. midwest would also remain fertile. If it gets warm and dry, though, the U.S. midwest becomes the great U.S. desert. At least once in earth’s past, a major extinction event was caused by the earth just getting too warm. It got warm and dry, and life just wasn’t sustainable around the equator.
If you look at this chart, we are in an abnormal cold spell: http://lh5.ggpht.com/Stepp.Matthew/RnltBA2TRhI/AAAAAAAAAAs/u3KF8zdJ6-Y/s800/globaltemptimeline.jpg
The earth’s average temperature is usually up around 22 deg C. Right now we’re down around 14 deg C. While recent warming trends do eerily follow mankind’s increase in population and pollution, there’s a rather large debate over whether global warming is purely a man-made thing or if it is just the earth doing one of its normal recoveries, the way it did during the cretaceous, permian, and silurian periods.
Global warming is probably better suited to great debates, and we probably shouldn’t hijack this thread any further on the subject unless it relates specifically to the OP.
I seem to dimly recall that the presence of water/oceans in large amounts was thought neccessary or at least very helpful in allowing for the process of plate tectonics. Or is that something I’ve just made up?
And oceans would seem to be highly neccessary to convert all that CO2 into carbonates.
So, in addition to being too close to the sun, lack of enough water and/or loosing too much of it too soon might not have helped Venus any.
Besides, Venus is not an Earth gone bad. Earth is a Venus gone soft ! Venus will kick anybody butt, though that Mercury is a fiesty little fracker.
The problem isn’t global warmth, it’s global warming. Sure, maybe when all’s said and done, Nebraska will end up with the climate that Texas has now, and Alberta will end up with the climate that Nebraska has now. We could live with that. But in the meanwhile, if a Nebraska farmer uses Nebraska farming methods and ends up with a Texas year, he’s likely to end up with crop failures due to not watering enough, or watering too much, or planting too late, or planting too early, or planting the wrong crops entirely, or so on. There are good farming practices for whatever climate you happen to get, but if the climate is changing too rapidly, then you can’t know ahead of time what those good farming practices are.
I wouldn’t go so far as to say it’s necessary, exactly, but it certainly is a factor - while the main driver of PT is density differences in rocks and hence the “pull” of subduction zones, I think without water-facilitated mantle melting that “conveyor belt” would freeze.
RE: plate tectonics, IIRC we’re pretty much alone in the Solar System as far as that goes. Even Io’s vulcanism is related to Jupiter’s tidal forces.
Oh, and here’s an article related to the “Venus sucks because it has no earthquakes” theory:
http://www.cosmosmagazine.com/news/1658/the-plate-tectonics-alien-worlds
BTW, as an aside. . . I just finished Simon Winchester’s excellent book “Krakatoa”. I was fascinated to learn that while an old theory, plate tectonics wasn’t definitively proven until the 1960s. I knew that it was a recent confirmation, but not THAT recent.
If the “conveyor belt” would freeze, doesnt that imply that its necessary? 
