The big paleontological news of last week was the announcement that fossil footprints have been discovered that predate - by about 20 million years - the previous contender for the earliest fossil evidence of tetrapods. Naturally, this announcement led almost immediately to a new round of "learning anything new about evolution means that Darwinism is totally wrong" claims from the Creationists.
Their complaints don't impress me much. There's very little difference between the Discovery Institute's "if there were tetrapod footprints 20 million years before Tiktaalik, how can something Tiktaalik-like have been an ancestor to tetrapods" line and the far older "if we descended from apes, why are their still apes" canard. If you're interested in another explanation of why you shouldn't be bothered by having ancestors and descendants alive at the same time, PZ's written a good one. I'm going to look at a different question.
It seems like someone finds some new fossil form somewhere every couple of years that changes our understanding of the evolution of some major group of plants or animals. Paleontology has been a serious scientific pursuit for the better part of the last two centuries. How is it that we continue to make so many spectacular new discoveries? Shouldn't we be at the point where we're just filling in the little gaps in the fossil record?
How thoroughly have we actually examined the fossil record? How much rock have we actually looked through in our quest to understand the evolution of the major branches of life?
Paleontology is time and labor intensive. When it comes to detecting fossils in rock, there is still no substitute for the Mark 1, Mod 0 eyeball. Finding fossils is a slow process. Removing fossils from rock is a slow process. Identifying and describing fossils is a slow process. It takes a lot of time to thoroughly examine a little bit of rock.
Still, there's been a lot of time and a lot of people working. So let's make some back-of-the-envelope calculations. I'm going to be very generous in my basic assumption.
Let's presume that one paleontologist can thoroughly examine 2 cubic meters of rock per day.
If that's the case, then 10,000 paleontologists, working continuously (365.25 days/year) for 150 years will have thoroughly examined 1,095,750,000 cubic meters of rock. That sounds like a lot, until you remember just how big the planet is. So let's put that figure in perspective.
According to the US Geological Survey, the explosive 18 May 1980 Mt. St. Helens eruption removed 0.67 cubic miles of the mountain. That converts, according to Google, to 2,792,681,820 cubic meters - that's more than twice the amount of rock that our hypothetical ten thousand paleontologists spent 150 years combing through.
Still surprised that we keep finding new tetrapod remains?