B
buffalo
Guest
http://t3.gstatic.com/images?q=tbn:ANd9GcSsdMJO6jvCQKwDYJmlXTRGiLlDlWlHtx7Hk67kVs6Gt-EPxFANc6yq5UXuThe Green River Formation: 10,000,000 layers of sediment a couple of millimeters thick each. And each layer representing one years deposition on a lake bed.
But can a lake survive continuously, undisturbed totally, as a lake for 10 million years. No ice-ages, no glaciers or ice sheets gouging the lake bed during all of that 10 million years.
How would I measure the deposition rates in the green river formation. Well, I might question the probabilities of a lake remaining as a lake continuously for 10 million years. And also it being undisturbed during all of that time.
I might look for other mechanisms for depositing sediment in regular consistant layers, other than as annual layers.
I might think they represent the tide flowing into a brackish lake carrying in calcarious sediment twice a day at high tides.
So that now you have 2 high tides a day or 730 high tides a year divided into 10,000,000 layers of sediment gives you an age for the lake of 13,699 years.
And as these layers are occasionally interspersed with interlocking layers of sediment from the shore I can then estimate the amount of time, in years, it took to lay down x amount of sediment on the shore.
Then I might find mammalian fossil jawbones in the shoreline sediment. The lower fossil I used to think was 5 million years older than the top fossil and that these fossils represented the evolution of a mammal over 5 million years.
But now I might see that the fossils were only 6,500 years apart and as a consequence they either showed remarkably speedy evolution or they did not show evolution at all.
That is if I were allowed to think about these things, that is.