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Let's say that, 2 million years prior to the present day, a meteor impacts roughly in the middle of the Strait of Gibraltar. It is large enough and strikes at sufficient velocity to create an impact crater 100 kilometers in diameter and 10 kilometers deep at its deepest point, which completely destroys the land on either side of the Strait and generally turns it into a gigantic crater that's a lot less of a strategic chokepoint.

Would such an impact wipe out all of the ancestor species of humanity that existed 2 million years ago via mechanisms such as a global winter, direct blast effects, or debris rainout? Failing all of them dying, would it at least kill enough of them that inbreeding would kill the species as a whole?

I recognize that the Chicxulub event is a leading contender for "the thing what wiped out the dinosaurs", and that the crater produced as a result of that is 150 kilometers across, suggesting that these two events would be at least vaguely comparable in magnitude, but I don't know if my impact event would wipe out proto-humans as effectively as whatever killed the dinosaurs killed them, as the former were, from what I can tell, somewhat more intelligent, and this is a smaller impactor.

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  • $\begingroup$ @John I'm pretty sure that was more like 200,000 years ago rather than 2 million. $\endgroup$
    – KEY_ABRADE
    Jul 30, 2021 at 20:52
  • $\begingroup$ Ha, yes, iIm an idiot. but the point still stands, Could it, yes, it is impossible to say for certain if it would, predicting extinction is tricky enough before you include wide spread intelligent hominids. $\endgroup$
    – John
    Jul 30, 2021 at 20:58
  • $\begingroup$ Early humans had several behavioral tendencies that might have allowed them to avoid extinction if they were far enough away. This nukes Western Europe and Northern Africa obviously, but if there were any as far away as modern day South Africa, then some would survive the initial impact and the immediate year or two after. $\endgroup$
    – John O
    Jul 30, 2021 at 21:18
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    $\begingroup$ The answer should be - "It may, but there is no way to say with certainty". $\endgroup$
    – Alexander
    Jul 30, 2021 at 21:21
  • $\begingroup$ @JohnO When you say "some would survive the initial impact and the immediate year or two after", do you mean "they'd die a year or two afterwards", or "they'd survive through then and potentially onwards"? $\endgroup$
    – KEY_ABRADE
    Jul 30, 2021 at 21:40

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I am going to throw my informed opinion in here and say that this scenario would not likely fully prevent the advent of modern man, but it may have delayed it enough that we wouldn't be asking this question today.

I will use simple timeline data and some insight from the Chicxulub event mentioned by the OP. My timeline source will come from the New York Times $(Wilford, 2002)$

Relying on prevailing theory:

5 ~ 7 Million YA

Somewhere in Africa ape-like animals that would become us began upright mobility.

2.5 Million YA

Basic toolmaking, such as flaking spearheads began.

2.4 Million YA

Earth enters the period of the Ice Ages. Global cooling and warming cycles will occur 17 times through the next 2.2 million years.

2 Million YA

BOOM! Your asteroid hits the Strait of Gibraltar. The sky goes dark, the earth cools down with no sun. Food supply runs low (lower than what the climate is already doing); survival of the fittest is handing out its biggest test.

I believe your asteroid is simply creating the same conditions we were conquering already, with ice ages. We had tools and shelter. Other species did not. Based on the Chicxulub event, We, the warm-blooded and mobile species, do win.

In the end, we are asking a question that has too little data for an objective answer. To cire the article one more time, The debate has never been so intense over what archaeologists see as the dawn of human culture

If Humanity began in Europe, maybe your impact could have snuffed us out. It is very likely that we have simply not searched wide and far enough to see how far we traveled in the few millions of years of mobility. A village in some beautiful Goldilocks island may have thrived and never needed more than thatch huts; their culture would never leave a footprint. But maybe they would be the ones far enough away from the damage to survive.

What would it take to answer Yes?

I think if we could reasonably say that human ancestors had not migrated around the globe, and were idle, uninquisitive creatures, just laying around in our pleasant little fields; then one big hit could have taken us out. The anthropological record tells us a different story. Our ancestors were never small, aboriginal and rare local attractions. As soon as we stood up, we walked away.

So your question is very specific: Would it kill all of humanity's ancestor species.

No, some or at least one ancestor would have won that selection event.

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