Sedimentary build-up.

[Mentat]

This may seem like a stupid question with an obvious answer, but I'm not really sure, so I thought I'd ask: Why do sedimentary strata always build up chronologically?

What I mean is: Why is it that geologists can trust, when dating a fossil or something, that the stratum has built up faithfully (meaning that the higher specimens are definitely newer than the lower ones)?

[Njorl]

I don't know much about the subject, but I have heard geologists talking about "sedimentary inversions". I think there are cases where the sediment "lies", but geologists can tell when it is lying.

I wouldn't be at all surprised to find out some sedimentary layers are put down in such a way as to be very deceptive, and fool researchers into making mistakes. Such mistakes might be considered extraordinary discoveries. Things like this are why extraordinary discoveries warrant extra scrutiny.

What is nastier is when remarkable circumstances hide important information. When an imperfect theory combines with a flawed experiment, and the flaws just happen to be consistent, a theory will be accepted without as much scrutiny.

Njorl

[Zero]

Originally posted by Mentat
This may seem like a stupid question with an obvious answer, but I'm not really sure, so I thought I'd ask: Why do sedimentary strata always build up chronologically?

What I mean is: Why is it that geologists can trust, when dating a fossil or something, that the stratum has built up faithfully (meaning that the higher specimens are definitely newer than the lower ones)? Ummm...I'm no geologist, but I have to ask: how else would they stack up? A layer of strata exists because it was in one place long enough to solidify, and experienced pressure from the layers above and below it. The act of creating a layer locks it into its place physically and chronologically.

[Zero]

Originally posted by Njorl
I don't know much about the subject, but I have heard geologists talking about "sedimentary inversions". I think there are cases where the sediment "lies", but geologists can tell when it is lying.

I wouldn't be at all surprised to find out some sedimentary layers are put down in such a way as to be very deceptive, and fool researchers into making mistakes. Such mistakes might be considered extraordinary discoveries. Things like this are why extraordinary discoveries warrant extra scrutiny.

What is nastier is when remarkable circumstances hide important information. When an imperfect theory combines with a flawed experiment, and the flaws just happen to be consistent, a theory will be accepted without as much scrutiny.

Njorl Hmmm...wouldn't those "inversions" have to be occuring in very specific circumstances, easily identified by geologists?

[Phobos]

It's obvious why sedimentation builds up chronologically. Newer stuff falls onto older stuff.

But you are right to question the reliability of it staying like that. Geologists are well aware of all the folding, faulting, flipping, cracking, mixing, etc. that rocks do. There are tell-tale signs of these processes...we'll need a geologist to give details, but it involves examining the regional geology (not making a conclusion from one point).

And then there's radiodating to verify chronology predicted by sedimentation models.

[Mentat]

Originally posted by Phobos
It's obvious why sedimentation builds up chronologically. Newer stuff falls onto older stuff.

But you are right to question the reliability of it staying like that. Geologists are well aware of all the folding, faulting, flipping, cracking, mixing, etc. that rocks do. There are tell-tale signs of these processes...we'll need a geologist to give details, but it involves examining the regional geology (not making a conclusion from one point).

And then there's radiodating to verify chronology predicted by sedimentation models.

Thanks for the responses (everybody)...yeah, I thought of verifying by radiocarbon and other such methods, after I posted the thread.