The “were you there?” fallacy

I was discussing the fossil record with a YEC friend on Twitter the other day. I pointed out to him that we never find whale fossils and plesiosaur fossils in the same strata, which is not what we would expect from Flood geology, since both occupied the same environment.

He said that’s just an assumption: how can we know, since nobody has ever observed plesiosaurs in their natural environment?

This is a fairly standard young-earth argument. Children are taught to impertinently ask their teachers, “Were you there?” when they are told about evolution or millions of years. It may sound persuasive to anyone who knows little or nothing about science, but it is not true.

Not having been there may mean that we don’t know everything about how plesiosaurs lived, but we most certainly do not know nothing. We know that they were marine animals for starters. Animals the size of a bus with flippers don’t live on land: they wouldn’t be able to get around. We also know they had worldwide distribution because their fossils are found everywhere. It doesn’t take a “secular” or a “materialist” worldview to see this, nor do you have to reject the possibility of miracles.

Plesiosaur_on_land
This could not have happened. (Image source: Wikimedia Commons)

These are facts that are obvious. Less obvious facts may require more advanced techniques to figure them out, and some of them may require assumptions to be made, but these assumptions are not untestable by any means.

In particular, it is quite straightforward to determine which physical processes operated at constant rates in the past and which did not. All you need to do is to cross-check different dating methods whose assumptions are independent of each other to see whether or not they give the same results.

There are many such cross-checks that we can make. Besides radiometric dating, we can also check tree rings, lake varves, ice cores, coral layers, and a whole lot more.

One particularly spectacular example comes from measuring rates of continental drift. In places such as the Hawaiian islands, the dates of lava flows increase linearly with distance from the hot spot in the earth’s crust over which the various islands have formed. In recent years, it has also become possible to measure continental drift directly using GPS. Everywhere we look, the measurements are exactly the same within the measured range of errors.

continental-drift-rate-comparisons
Continental drift rates as measured by radiometric dating versus direct laser measurements. Figure modified from Robbins et al., 1993. Source: thenaturalhistorian.com

Scientists do not blindly assume that all geological rates were constant. On the contrary, they acknowledge that some rates must have changed over time. For example, that is why they do not consider that the amount of salt in the sea tells us anything about the age of the earth: its rate of change is simply too variable, there are too many unknowns, and a state of equilibrium lies well within the error bars. On the other hand, there are very good reasons, both theoretical and observational, to believe that nuclear decay rates have always been the same in the past as they are today. These cross-checks are just one such reason.

Next time, we’ll take a look at how the young-earth organisations have responded to these cross-checks. Their response is quite bizarre and completely misses the point.

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