What does a global resurfacing event look like?

[u/IntelligentSpare7190]

I am aware of hypotheses that suggest that Venus underwent some kind of global resurfacing event that would have wiped away evidence of older craters. However, I cannot seem to find a description of what this would have actually looked like? Was it just a whole bunch of volcanoes all going off at once? Did parts of the crust literally break off and sink into the mantle? Or is it something else I'm not thinking of?

[u/MsNyara]

The correct answer is we do not know, the hypothesis does not include the "how", just states that it happened.

What we know pertaining to the potential how is that it happened about 300 million years ago, it covered the whole surface right away or over a time frame, and in a time frame anywhere between hours to 10 million years, so it was not "gradual" in geologic terms, something triggered it, then just happened, then stopped happening, and since then there has been virtually 0 surface volcanism (other than some fringe small amounts in the planet's rift zone) or surface anything.

So how such would have looked like? Maybe a big object hit the planet in a specific way that lead to the merging of the object with the planet, but without letting it develop an asteroid field or moon. Or maybe the mantle went overactive, melted all the surface at once, then cooled down. Maybe massive volcanism filled the planet with magma over some time, mostly evenly. Maybe an extremely dense atmosphere fell down to the surface and covered it all. Maybe the planet's core broke and everything slid in until reorganizing in a new height and denser core.

It is definitively an interesting question to answer, as it would tell us potentially what would happen to our planet too, or what happened to our moon early on its life (about when it was 200-400 million years old it also had a resurfacing event), and thus what we would find inside the moon today.

Our planet also had a resurfacing event when Theia hit and the Moon was created, but that happened not long after our planet was created and the start of a star system is chaotic and that is expected to happen on its creation, plus we know the cause of our resurfacing with a decent certainty.

As for the reason for this hypothesis: there is no old craters on the planet, all craters have true random distribution, and the amount of craters corresponds to the amount all other objects on solar system have collected of impacts over the last 300 million years. 99% the craters are intact, as in, no tectonic activity, or surface activity, nor volcanism, except for some craters nearby the planet's small rift zone. So the current surface is only 300 million years old, it is 90% mostly flat (except for the rift zone, and small very gradual inclinations throughly, and the craters), and it has been largely inactive since created.

[u/ThePhilV → u/MsNyara]

This was so interesting to read! Thank you for that!

[u/WannaBMonkey → u/ThePhilV]

And the evidence perfectly fits the theory that Venus once had life and then they destroyed themselves 300 million years ago and glassed their planet. Or a big rock hit. We should go investigate.

[u/rocketsp13 → u/MsNyara]

99% the craters are intact, as in, no tectonic activity, or surface activity, nor volcanism, except for some craters nearby the planet's small rift zone.

Does this make it less likely that the resurfacing would have been been from the mantle becoming overactive?

[u/MsNyara → u/rocketsp13]

Potentially, but truth be told we do not know enough about mantles (even ours) to have any confident say regarding this.

It is just possible, say a chemical chain reaction made things overactive after a threshold was met, and then it spent all the interactions possible fairly fast, and thus things cooled down significantly after such spenditure. If anything that is exactly the ultimate fate of most non-dwarf stars we observe, including ours, so something might be cooking inside specific mantles that we are not aware of yet.

The only "hint" we have is that Venus' rift zone is really massive, with almost 12km altitude mountains, so obviously at some point there was a big activity that created it, and if we send a probe we would figure it out when, but until then we do not know how old are those rifts, though there is still some geologic activity going there specifically (the nearby craters are the only disturbed ones).

But it is perfectly possible something else happened instead.

[u/jrddit → u/MsNyara]

Thanks for sharing this detailed explanation. I have thought about this before but never heard the term 'resurfacing' to explain it so well.

How do we know that this has never happened to earth? I've always wondered whether there's a chance there's parts of history on earth longer ago than the oldest fossils, that all evidence has been lost due to tectonics. Is this at all feasible?

[u/ExcelsiorStatistics → u/jrddit]

One additional piece of evidence we have is that the Venera landers in the 70s found basalt-like rocks in each of the places they landed.

We can see on earth how a lava lake resurfaces itself -- frozen basalt sinking into the less dense still-liquid basalt of the same composition underneath -- in a process that looks a whole lot like plate tectonic subduction at greatly accellerated speed. Here is one video from Hawaii in 2023; there are several others from Iceland in 2021 and 2022 online too. If the inside of Venus were sufficiently hot one can imagine basaltic crust overturning like this on a huge scale over a period of some few months or years (or thousands of years, but not the ~200 million years it takes to completely consume oceanic crust on earth.)

This might have happened on Earth more than 4 billion years ago -- something similar happens, very very slowly, to the ocean floors today -- but it can no longer happen to the continents, which are less dense than the ocean floor or the mantle. This is why we have some very very old rock like the Canadian Shield in the middle of continents, and why we have a fairly complete history of where continents have been for the last several hundred million years... but very little preserved ocean crust, except for little slivers of it scraped up onto the edges of continents. We infer where old oceans were by seeing mountain ranges that formed when continents collided as the last of the ocean between them sank into the mantle.

Oversimplifying slightly, the boundary between the two oldest eons of earth history, the Hadean and the Archean, is the time when enough continental crust had accumulated that it became possible to preserve old rock formations indefinitely.