At the recently concluded Geological Society of America meeting in Denver Dr. Richard Ernst, Scientist in Residence, in the Dept of Earth Sciences at Carleton, together with NASA scientists Dr. Michael Way and Jeffrey Scargle, presented evidence that in deep geologic time both Venus and Earth were water worlds with relatively stable and temperate climates.
While Earth’s climate remained habitable Venus has a hostile CO2-dominated atmosphere with a 450°C surface temperature hot enough to melt lead. They argue that the reason why these sister planet’s climates have diverged so dramatically is because Venus got unlucky. Both worlds have periodically experienced huge volcanic eruptions that form often huge basalt-covered areas called Large Igneous Provinces (LIPS). On Earth one of the largest LIP events caused a massive extinction event 252 million years ago at the end of the Permian Period, where more than 80% of marine species went extinct. Some LIP events are large, and others are small, and they have occurred randomly at about 15-million-year intervals.
Through an unlucky roll of galactic dice Ernst and colleagues hypothesize that at some time in the past Venus was subjected to multiple simultaneous LIP events that raised Venus’s surface temperature past a high-temperature tipping point. With the evaporation of water from Venusian oceans enormous quantities of water vapor, an important greenhouse gas, would have raised the atmospheric temperature even further. With no oceans left plate tectonics would also have ground to a halt without the presence of water to make the oceanic crust heavy enough to sink below adjacent continental crust. These CO2-bearing sediments would thereafter have remained on the surface and exposed to the atmosphere.
This resulted in Venus remaining hot and dry indefinitely. Earth has been lucky thus far to not have the confluence of LIP events that forever changed the climate of Venus. In the context of the vastness of geologic time though how long will that luck hold out?
The full article in the Economist may be read here: https://www.economist.com/science-and-technology/2022/10/19/unlucky-lips-may-explain-venuss-hostile-environment