Geologic Paradox

4.6 Billion years old. That's the closest we can come to determining the age of the world in which we live. Pretty amazing don't you think? Human civilization began a mere 6 millenia ago, the Sumerians being the earliest known records. Yet the spinning blue ball on which our play is set has been around 166,666 times longer!

I mean, it boggles the mind doesn't it? Because for most of that time, we have no record of anything going on. Until the Cambrian Explosion 530 Million years ago when BLAM! all these fossils suddenly appeared out of nowhere. (That's why they call it an 'explosion'.) But then it's not like there were witnesses to all of this. You know, I've often wondered how we arrive at that number.

It can't be a result of Radio-Carbon Dating, since that can only be used on living organisms or things that had once been living. A complication made more problematic because the half life of C-14 is only about 5,700 years, a little less than the whole life span of human history which, as we've noted is but a drop in the bucket of Earth's lifetime.

For the answer, we have to turn to Geology. The science of Geology studies the strata of rock layers and sediment. It's kind of like looking at the rings of a tree. In general, the lower the rock layer the older it is. So, how do we determine the date range of the particular rock layer we're looking at. Well, that's simple. We look at the fossils in the layers of rock. Since we know the age of the fossils we're finding, we can reasonably assume that the layer of rock is at least that old and that, barring any major upheaval or overturning in plate tectonics, the layers underneath are even older still.

So if we use fossil dating to determine how old the layer of rock is, how do we determine the age of the fossil we're looking at? Well that's easy! We determine the age of the fossil based upon what strata of rock its found in. And then of course we...

...wait a sec.

(slowly and thoughtfully) We determine the date of the rock strata by the fossils found in them and the layers above or below. (okay) Then...we know how old the fossils are...by how old the layers of rocks are...

...hmmm. A paradox.

"The intelligent layman has long suspected circular reasoning in the use of rocks to date fossils and fossils to date rocks. The geologist has never bothered to think of a good reply." - J.E. O'Rourke American Journal of Science Jan. 1976 p.48