It's quite obvious that the Earth is going through a climate change that may have effects far more serious than a slight heating of the atmosphere. A prolonged heating, as a new study suggests, could bring our planet into a situation similar to that of Venus, whose crust became locked in place.
"The heat required goes far beyond anything we expect from human-induced climate change, but things like volcanic activity and changes in the Sun's luminosity could lead to this level of heating. Our goal was to establish an upper limit of naturally generated climate variation beyond which the entire solid planet would respond", said associate professor of Earth science at Rice University and leader of the study, Adrian Lenardic.
Venus is rather similar to Earth, having roughly the same relative size and mass, both bearing thick atmospheres. The difference between Earth and Venus is that the latter is much hotter than our planet and doesn't seem to present any tectonic activity. The study was aimed towards the relation between the excessive heat experienced on our twin and its seemingly absent tectonic movement.
Venus' atmosphere is about 100 times denser than that of Earth and has a high carbon dioxide concentration that is probably responsible for a global warming effect heating the planet. Surprising as it may seem, Venus actually has a surface temperature greater than Mercury, although it's twice as far from the Sun.
Most of the carbon on Earth is trapped either beneath the surface or inside bodies of water such as seas and oceans. The movement of the plate tectonics ensures that this carbon is being recycled in the inner regions of the planet and returned into the mantle, a flowing layer of rock extending below the crust between as little as 48 to 2880 kilometers.
"We found the Earth's plate tectonics could become unstable if the surface temperature rose by 37.7 degrees Celsius or more for a few million years. The time period and the rise in temperatures, while drastic for humans, are not unreasonable on a geologic scale, particularly compared to what scientists previously thought would be required to affect a planet's geodynamics", said Lenardic.
It is widely believed that Earth's tectonic plates are both stable and self-correcting, under the assumption that heat from the mantle can efficiently escape through the crust. Heat convection generates a flowing pattern in the mantle which is transmitted to the tectonic plates, thus keeping them in motion. However, a rise in surface temperature can also affect temperature inside the planet and could eventually lead to a stop in the plate tectonics.
"We found a corresponding spike in volcanic activity could accompany the initial locking of the tectonic plates. This may explain the large percentage of volcanic plains that we find on Venus", Lenardic explains.
The apparent inactivity of Venus' plate tectonics was previously blamed on the lack of water which could have provided lubrication. According to the study, on Earth water would be able to exist freely at the temperatures required to stop the movement of the plate tectonics.
"The water doesn't have to boil away for irrevocable heating to occur. The cycle of heating can be kicked off long before that happens. All that's required is enough prolonged surface heating to cause a feedback loop in the planet's mantle convection cycle", concluded Lenardic.
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