That is, is there any point in the geologic record since the Cambrian where we have ZERO fossil evidence of life for that interval? My intuitive guess would be “no” because of the ubiquity of life in the oceans and oceanic sediments (especially diatoms). But can every single let’s-say million year interval for the past 500 million years be accounted for?
I don’t know the answer, but I’d expect that the range of dating uncertainty would get bigger as you go back in time. If you can only date a fossil to +/- 50 million years 1 billion years ago, that will reduce the chance that any interval won’t be in some range.
I don’t know from fossils, but I do know that treating numbers that are inherently uncertain as if they are absolute leads to all sorts of problems.
You probably know this, but it does affect the answer to your very interesting question.
Fortunately, the Cambrian was not a billion years ago; it was about half that (541.0 ± 1.0 to 485.4 ± 1.9 million years ago). Before the Cambrian, life was pretty much all unicellular and there’s very little in the way of fossils of that. The Cambrian is when multicellular life really got going.
AFAIK, the answer to the OP is that there are no significant gaps in the fossil record. There’s no one place that has a complete record, of course. But they can find fossils for every era by looking in many places. After all, they have the entire world to look for them.
I would guess that the fossil record must be sparse after mass extinction events, but I don’t know if it’s zero. And that wouldn’t mean anything other than there were fewer animals to be fossilized around then.
Fewer species perhaps, but the ones that were around might be common.
Even if there were gaps, they would be pretty meningless. Some species such as Stromatolites have been around pretty much unchanged since the PreCambrian.
Gaps to a fossil record are the rule, not the exception. There is no continuous fossil record, or even a continuous stratigraphic column beginning from pre-cambrian times. There’s always a hiatus (called an unconformity.)
Right, fewer animals in total, I meant. Thanks for clarifying.
Yes, but the OP is not asking about local gaps, but complete gaps for a certain time period. Usually when erosion is going on in one place (which causes the unconformity), deposition is going on somewhere else. In fact, this situation virtually guarantees that there will be some sedimentary deposits from all time periods.
Sorry, I should’t have used the phtrase “fossil record”. Of course there are gaps in that, since not all genera have fossilized representatives, or perhaps some have but we haven’t found them. I should have said “stratigraphic record”. There’s no significant gaps in that, although you have look in a number of different places to get the whole thing.
ETA: Just noticed the phrase was used in the thread title. But the OP talks about the geologic record. These are two different things.
Been googling “world-wide unconformities.” The term is used by geologists often enough but it does not mean absolutely no sedimentation and fossilization of any organism that died during the period. Rather, they mean the break is observed in many parts of the world but not the whole world.
I was watching a show on PBS once and the host was walking up a hill showing where there were fossils everywhere he looked and pointed … up to a certain elevation … above which the land was completely devoid of any fossils … very dramatic. It was the Parmesan Distinction Event or some such. So at least on that particular hillside, there was a gap in the fossil record.
A million years is often less than the uncertainty on our dating, so it’s impossible to say for sure that there hasn’t been a worldwide unconformity since the Cambrian - but it doesn’t look like there has been. And the telling bit, for me, is that after the so-called “Cambrian Explosion”, it’s been an ordered spread and evolutionary development ever since - there’s no place for a gap to exist, no sudden jumps in organization level or introduction of new taxa ex nihilo, the way you seem to get after the end of the Ediacaran (with the possible exception of the Bryozoa, but they’re hardly revolutionary). The only comparable event is the evolution of land plants, I think.
As has been noted, virtually every stratigraphic sequence has unconformities (times of no deposition or of erosion) or strata that contain few if any fossils. However, there seem to be no unconformities at a global level, and even after major extinction events the succeeding strata usually contain at least some fossils. (I presume your joke is referring to the Permian Mass Extinction, the largest one on record.)
