Originally posted by BetweenMyths
Did you know that the geological column ... The dates of these time periods were just pulled out of thin air.
I'd like to say thats wrong.
The dates are of course an estimation, but based on fact.
Imagine say, the delta of the River Nile. Sediment is being slowwwwwly deposited there, just as it has for the last few thousand years. Constantly the
same, but not - just changing very slowly.
Anyways - within this sediment, every now and again, maybe a leaf, or a small creature, like a shellfish, will die and its body become encased in
sediment.
The only way this sediment will turn into rock is through compaction over
millions of years. Squashed, subjected to enormous pressures, heat,
et al. Eventually it will become rock, deep within the earths crust.
Tectonic activity, and things related to densities of surrounding rock/landmass/ocean
could mean that a few million years later the rock is
back at the surface (this process is called uplift).
And if the right bit of rock becomes exposed to the elements, someone might find the fossil.
Obviously, we don't know how long that has taken. What we can look at though, is the rate at which sediment is being deposited today - and from the
composition of this fossil we just found, we can have a good go at deciding the environment in which it was deposited.
Find a similar environment in existance today, look at the rate of deposition. Do a few sums, work out how much mass would need to be above it for the
relevant compaction to work, then look how much rock is visible above and below the fossil - and how similar compositions are being deposited today
and at what rate.
Then take your data, and trace back, very carefully, and you get a reasonable estimation at the age of the rock.
Fossil formation is something that takes a long time - very little, if any, organic material remains, it has instead been replaced by certain minerals
contained within the sediment (that turns into the rock.. eventually).
Some of this is guesswork, but it doesnt take a genius to figure out that for a rock to get heavy enough to sink into the earth, then move to an area
of denser material to allow for uplift to occur, then exposation of the rock and subsequent discovery of the fossil - it won't happen in less than
6,000 years, I promise you that.
Its impossible for a fossil to be formed in anything less than a few million years... and all this is the same reason for gaps in the fossil record -
not all of them make it back up to the surface.
Read through that again, slowly. It makes sense. Its based on scientific fact (I can't be bothered finding sources - I learned it myself by slogging
out a long, tedious geology course - and also have a basic understanding of physics, which helps) - but, of course, if you believe a 2000 year old
book thats been fiddled constantly over the ages as opposed to reason and verifiable fact, then feel free.
EDIT TO ADD:
PS - Carbon dating can't tell you how old a rock is. It tells you how long since something died. However, if theres not enough carbon left for that
to work, then other radioactive methods can be used - but on something completely fossilised, or
mineralised if you prefer (as the original
material has been replaced in the same structure by non-organic minerals), it is impossible, and you have to work back as described above, to figure
out how old the rock
could be.
[edit on 10/8/09 by selfisolated]