Extinction Equilibrium: 50%

The last time I asked a worldbuilding extinction question, I asked on what sorts of factors would create an extinction event in which 96% of all terrestrial species and only 70% of marine species died out in a short span of time. In there, I got only two answers--a rogue ice age (not interesting, personally) and a gamma ray burst from a nearby supernova (worth exploring, but that raises another question--how long would it take for the atmosphere re-establish itself?)

But now we investigate a different kind of catastrophe--an extinction equilibrium, in which the death rates of terrestrial and marine species are the same. There are countless inexhaustible variables on this, so let's narrow it down to one extinction event with three different options.

In this episode, we investigate the extinction of 50% of all terrestrial species and 50% of all marine species, the minimum requirement for an extinction event to be "mass".

What combination of factors would create any of the specified damage?

Just a reminder, this question does not ask how long it would take for life to recover, who would fill in the vacant niches, etc. The question is what would cause an extinction event as described in the paragraph above. It doesn't matter when it happened. But no man-made!

Also, a similar-looking question has been deleted, so this is not a duplicate.

posted over 6 years ago

JohnWDailey‭

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