It's pretty tricky to find out, yeah. And new evidence is coming in all the time. All the methods are either floors (a fossil at X date proves a species existed then, but lack of fossils found yet might be inconclusive) or estimates (like molecular clock techniques). Dating fossils themselves (or rather the rocks they're buried in) isn't always easy or possible. For more out-of-the-way species, if anyone has bothered trying to figure out the age it's likely buried in scientific sources that are tricky for novices to find or search, and maybe under debate.

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psychoslave 3 hours ago | parent [-]

That make wonder, how many fossils there might be at total on earth, and with current trend, how much time would humanity should continue to survive before those remaining will approach zero, if fossil formation as a known rate.

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throwup238 3 hours ago | parent | next [-]

> how many fossils there might be at total on earth

The number is both incalculable and vague - is a shark tooth enough to count as a fossil? How about diatoms and other microfossils?

Diatomaceous earth alone contains around 10^6-10^7 frustules (the shell of a diatom) per gram. If you count them as fossils then the lower bound is 10^18 fossils per year just in diatomaceous earth production (the fossils are ancient but we produce nearly a million tons a year in diatomaceous earth).

	▲	hnlmorg 3 hours ago \| parent [-]
		If you have a fossil, and break it in half, then do you now have two fossils?

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bubblewand 3 hours ago | parent | prev [-]

Immense numbers. Quarries destroy them by the (enormous) truckload all the time, unexamined, god knows what cool unknown stuff has been ground up. Entire kinds of rock are basically made of fossils, not even always the really tiny kind (note: fossils can be microscopic!)

Then consider what's buried under the sea, totally inaccessible. Or under the ice at the poles.

It's a lot of fossils. And that's without even getting into questions like "what counts as a fossil for these purposes?", just any halfway sensible answer is going to leave you with an unfathomably big number, no need to even dig (ha, ha) into the specifics.

The places scientists go to dig up fossils are mostly where a particular stratum happens to exist (the crust gets recycled, so much of the oldest stuff is simply gone in most of the world) and happens to be exposed near the surface. Those same kinds of (for the more common strata, anyway) exist all over the place, just buried too deep to get at except, sometimes, during commercial excavation for things like mining (and then most of it's just gonna be destroyed without a look).