In Niven and Pournelle’s classic 1977 SF novel, Lucifer’s Hammer, there’s an early scene where, as it becomes increasingly clear the comet Hamner-Brown is on a collision course with Earth, some scientists speculate this might have happened before: Look at the oddly circular shape of the Gulf of Mexico, or the Sea of Japan – might they be giant impact craters?
Has science ever investigated this possibility? What’s the likelihood? (And why is it that the Gulf of Mexico, right next door to the Islands of the Caribbean, is so conspicuously lacking in islands?)
(Putting this in GD because, although a purely scientific question, it may be one with no well-established or uncontroversial answer.)
I believe it has been investigated, at least in context of looking for the “Dinosaur Killer” impact. The seas are particular fast at erasing impact craters, but it must be possible as we have a confirmed crater in Africa of 190 miles across (Vredefort crater) and a possible one in Antarctica of 312 miles (Wilkes Land crater).
If you are specifically asking about the Gulf of Mexico & the Sea of Japan I cannot help at all.
Yes, rigorously though unintentionallly. Rocks have different characteristics depending on how they form. Rocks thrown up by an impact would be largely metamorphic, that is they started out as one type of rock and the vast heat and pressure of the impact transformed them into another type. In contrast the islands of japan are mostly igneus rock IIRC, IOW they formed mostly from lava/magma. That isn’t consistent with the sea having been formed form a meteor impact, but it is perfectly consistent with the sea having been formed on between two plates.
We can also trace the movement of the sea floor due to the movement of those plates, and there is no sighn of any impact.
Different modes of formation.
The answer is well established and not the least controversial. We have a pretty good handle on the gross geology of most of the world.
I’ve heard the Gulf of Mexico = Impact Crater theory before, and it’s true, the Gulf does look suspiciously oval-shaped and island-free, but I think the consensus among geologists is that it formed naturally via erosion & plate techtonics like any other major body of water. Part of the confusion probably comes from the 110-mile wide Yucatan Impact Crater, which lies partly in the Gulf and is believed to be responsible for killing off the dinosaurs.
I read that all our ocean basins may be a result of the hypothetical massive impact that formed the moon - that wasn’t an asteroid, though, but a planet about the size of Mars. Of course, the plates that didn’t get knocked into space have slid around a lot since then and it’s not one big hole anymore.
The trouble is that any impact large enough to leave behind an impact crater as large as the Gulf of Mexico is also going to be large enough to put the survival of the biosphere in question. It would make the KT impact look trivial. It might not sterilize the Earth, but if the temperature of the Earth’s surface is raised to the point where all the oceans boil, there’s not going to be anything left except perhaps a few extremophile prokaryotes.
Then consider the age of the Gulf of Mexico. It’s not that old. Only 250 million years ago North America, South America, Europe and Africa were joined into one continent. Any impact crater that could form something like the Gulf of Mexico would pretty much have to have occured in pre-Cambrian times, and for all we know there were dozens of impacts as large as the KT or larger, we just don’t notice them because there were no metazoans to wipe out. And an impact that old isn’t likely to leave many traces after 650 million years. Given that the summit of Mt Everest is marine limestone, it’s pretty likely that any random spot on the earth has been altered beyond recognition since that time. Only a few really old rocks still remain unaltered from Earth’s early history.
My understanding is that mascons found around or in the Hudson Bay area have lent support to the theory that part of the bay may be the remains of an impact crater, too.