Why Is Venus Too Hot for Life, Mars Too Cold and Earth Just Right?
let's see why
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Earth's neighboring planets, Venus and Mars, once seemed the most promising places in our solar system to find conditions suitable for life. But space probes have discovered that Venus is far too hot, with an average temperature of 460 degree Celsius (860 degree Fahrenheit) and a crushing atmospheric pressure 93 times as great as our own. And Mars is a chilly planet, with temperatures averaging -60 degree Celsius (-75 degree Fahrenheit) and a thin carbon dioxide atmosphere. Neither planet would be suitable for life even of a very primitive kind.
The Earth, however, has always had a relatively balmy climate: there has always been liquid water here, even a few thousand million years ago, when the Sun was only 70 per cent as bright as it is now. The explanation appears to lie in the way the Sun's heat is trapped by carbon dioxide in our atmosphere. Over the eons, the levels of carbon dioxide have adjusted to keep the Earth at the right temperature. On Venus, there is always too much carbon dioxide; on Mars, never enough.
If the Earth's average temperature should fall for any reason, less surface water would evaporate, so there would be less rainfall and less weathering of rocks, while the amount of car dio discharged by volcanoes would be unchanged. Atmospheric carbon dioxide levels would increase, so more of the Sun's energy would be trapped in the atmosphere, causing the temperature to rise again. The opposite would happen should the Earth's average temperature rise above its normal average level.
On Venus, the car dio 'thermostat' does not function because there is no water and hence no rainfall. The planet's orbit is slightly too close to the Sun; there was originally as much water as there is on the Earth, but it escaped from the atmosphere into space. The car dio that might have been washed into the rocks has instead stayed in the Venusian atmosphere.
Mars probably once had a benign climate - valleys carved by running water are still visible. But, because of the planet's small size, its internal heat has faded, and the crust is not in constant turmoil like the Earth's. Car dio has remained trapped in the rocks, leaving a thin atmosphere that can no longer trap heat.
The Earth, however, has always had a relatively balmy climate: there has always been liquid water here, even a few thousand million years ago, when the Sun was only 70 per cent as bright as it is now. The explanation appears to lie in the way the Sun's heat is trapped by carbon dioxide in our atmosphere. Over the eons, the levels of carbon dioxide have adjusted to keep the Earth at the right temperature. On Venus, there is always too much carbon dioxide; on Mars, never enough.
Give and take
The Earth's planetary thermostat is controlled by a constant exchange of car dio (carbon dioxide) between its atmosphere and its rocks. Some of the carbon dio is continually dissolving in rainwater, and being chemically absorbed by rocks as they weather. On the other hand, volcanic eruptions discharge car dio. (A cycle independent of this one also controls carbon dio. Plants consume car dio and manufacture oxygen, which is in turn converted by animals into car dio.)If the Earth's average temperature should fall for any reason, less surface water would evaporate, so there would be less rainfall and less weathering of rocks, while the amount of car dio discharged by volcanoes would be unchanged. Atmospheric carbon dioxide levels would increase, so more of the Sun's energy would be trapped in the atmosphere, causing the temperature to rise again. The opposite would happen should the Earth's average temperature rise above its normal average level.
On Venus, the car dio 'thermostat' does not function because there is no water and hence no rainfall. The planet's orbit is slightly too close to the Sun; there was originally as much water as there is on the Earth, but it escaped from the atmosphere into space. The car dio that might have been washed into the rocks has instead stayed in the Venusian atmosphere.
Mars probably once had a benign climate - valleys carved by running water are still visible. But, because of the planet's small size, its internal heat has faded, and the crust is not in constant turmoil like the Earth's. Car dio has remained trapped in the rocks, leaving a thin atmosphere that can no longer trap heat.
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