Global Resurfacing Event
It is hypothesized that Venus underwent some sort of global resurfacing about 300–500 million years ago, though no Venusian rock has ever been dated.
One possible explanation for this event is that it is part of a cyclic process on Venus. On Earth, plate tectonics allows heat to escape from the mantle. However, Venus has no evidence of plate tectonics, so this theory states that the interior of the planet heats up (due to the decay of radioactive elements) until material in the mantle is hot enough to force its way to the surface. The subsequent resurfacing event covers most or all of the planet with lava, until the mantle is cool enough for the process to start over.
There are several other attributes of Venus that this model can help explain. Venus's lack of a magnetic field is puzzling, as Venus is similar to Earth in size, and presumably composition. However, it can be explained by a core that is not losing heat. Also, Venus has a much higher deuterium to hydrogen ratio in its atmosphere than do the Earth or comets. Atmospheric escape is one of the very few processes that differentiate between the deuterium and hydrogen. The extremely high ratio implies that there were large amounts of water in Venus's atmosphere more recently than the beginning of the solar system, and that a massive eruption would release large quantities of water (as well as other compounds, for example the sulfur that leads to the sulfuric acid clouds of Venus).
More evidence is needed to put the theory of global resurfacing of Venus on firm ground. However, several different indications support it, and it is hard to explain the crater pattern of Venus without something at least vaguely resembling this idea.
Read more about this topic: Geology Of Venus
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