The Geological Column

Another one for Sirius Knott today, this time concerining the geological column. As ever, and I cannot stress this enough, criticism or corrections are welcomed – if you know more about this than I do and spot an error (or several!), please let me know.

The geologic column (or geologic record) is the sum total of the layers of rock that make up the Earth’s crust (‘strata’), the fossils they contain and any other materials found within them. The column itself is a cross-section of strata, displaying different layers of rocks with different compositions and appearances. The column can tell us an enormous amount about the Earth’s history – its composition over time and in different locations, the tectonic forces that shape it, and the life forms that existed in the distant past.

 

 

 

The Grand Canyon

 

 

 

Unfortunately, the geologic column is never perfect; tectonic activity constantly ‘recycles’ the Earth’s crust through subduction, where one plate is pushed under another and melted. On top of that, there are numerous tectonic processes that can warp the geologic column, in some cases even inverting it. Creationists like to pretend that this is geology’s dirty little secret, but it isn’t; almost any discussion of the geologic column will include this information, and any secondary level Geography course includes the study of these tectonic processes. Despite what Knott seems to think, they are well understood by scientists and are certainly not a serious problem for geology. 

Despite these shortcomings (what Darwin referred to as ‘the imperfection of the Geological Record’), the study of rock layers and their composition is enormously useful. The guiding principle of such study is the ‘Law of Superposition’, which states that ‘Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top’. The law was first proposed in the 11th century, but is more commonly associated with 17th century scientist Nicolas Steno. 

Before I go further, I must lay to rest one of the most common fallacies associated with the geologic column, and one that Knott commits frequently. It is often claimed that modern geology is built upon ‘evolutionary presuppositions’, and that (non ‘flood’) geologists lie about their data in order to perpetuate ‘Darwinism’. This is nonsense; the order of the geologic column, along with the relative ages of each strata and their associated fossils, were all confirmed long before evolution became a dominant theory in biology. Nicolas Steno himself believed in the Genesis account of a global flood, as did most scientists of that time. However, it was his first steps into dating the rock layers of the Earth that lead to the eventual abandonement of the global flood idea and the eventual discovery of plate tectonics. 

I mentioned the ‘relative dates’ of strata, and here we come to the most contentious area of geology where Creationists are concerned: dating. Flood geology exists because it provides a plausible (for Creationists) explanation for how the various geological features of the Earth could exist in a world that is just over 6,000 years old. There are two general dating principles, ‘relative’ (determining the age of strata in relation to each other, in which the Law of Superposition obviously comes in useful) and ‘absolute’ (which seeks to approximate a sample’s actual age). I’ll go through the more common mistakes that Creationists make about this area of geology:

1) Circular reasoning. Creationists claim that ‘fossils date the rocks, and rocks date the fossils’, which is yet another curious example of them accusing scientists of behaving in a way that is so stupid, one has to wonder why the entire world hasn’t copped on to them yet. Certain fossils are found only in certain kinds of rock layers, and in some cases help to define them (like the Cambrian). These fossils appear so regularly in the same places that they can be used as a reasonably accurate guide to whether a rock layer is of the same era as another, similar one on the other side of the world. Radiometric dating methods confirm these estimates. 

2) Radiometric dating is highly flawed. I’ve covered this one before, but I’ll go over it again briefly. Radiometric dating is the measure of naturally occurring radioactive isotopes and their products, which they produce via radioactive decay (a well understood phenomenon). By measuring the amount of the original isotope present in a rock sample and comparing it to the amount of the ‘daughter’ isotope, it’s possible to obtain a rough estimate of the sample’s age. Creationists object to this method on two grounds: that an assumption must be made about the amount of daughter isotope present in the sample when it formed and that chemical or physical conditions can alter the decay rates of radioactive isotopes.

The first is only partially true; while some dating methods do require one to assume that a sample has not been contaminated by the daughter isotope, isometric dating (more on that in the post I linked to above) does not. The second is completely false; decay rates cannot be altered in this way, and have not been routinely increased by factors of thousands or millions (as claimed by some Creationists) except in certain high energy physics experiments and under conditions that rocks would ever have been subject to during or after their formation. 

3) The fossil record is ‘imaginary’. I’ll go into more detail on the fossil record at a later date, but it is often claimed that the fossil record suggests evolution only if one assumes evolution. This again ignores the fact that rock strata and their associated fossils were discovered long before Darwin ever wrote On the Origin of Species – it took evolution to explain what had already been discovered, and it remains the best explanation for what the fossil record tells us. 

 

There are of course still gaps in our knowledge of the history of the Earth, as there are in any other branch of  science, but major refinements to the geological record are now rare and revisions to ages of strata or fossils tend to go upwards rather than downwards. It is very unlikely at this point that geologists will turn out to have been so wrong as to mistake a six thousand year old Earth for one that is several billion years old. 

Some time over the next two days I’ll adress the rest of Knott’s post, including fossilisation, the infamous Cambrian explosion and flood geology.

EDIT: Knott has apparently reversed his position and no longer wants me to explain why he’s wrong, despite asking me to do exactly that several times, and has gone as far as to suggest that I’m a ‘cyberstalker’ who he wants to get rid of. I’m not entirely sure what to make of that, but his blog is such a rich trove of Creationist propaganda that I’ll continue to base posts off of it, without directly linking to it. It won’t change the content any, since I’ve already decided to cover Creationist mistakes that I had thought didn’t need to be covered.