I played a lot of “sandlot” sports while growing up. Part of the experience was the pre-game ritual of choosing sides. Unfortunately, if there was an odd number of kids, someone would get left out. As a Christian apologist, there are times when I feel like the odd-man out.
For instance, Christians’ scientific discussions about the age of the universe or earth typically center on astronomy and geology, both areas outside my expertise. But once in awhile, I get to join in when the debate involves biological evidence. As a biochemist, that is something I can weigh-in on.
Cuttlefish fossils recently recovered in Mississippi were dated by researchers to be 35 million years old. However, a young-earth creationist recently claimed that chitin associated with the fossils demonstrates that these remains must be only a few thousand years old. Presumably, chitin, an organic material that makes up the beaks of cephalopods (such as cuttlefish) and other hard structures in mollusks, would have broken down completely after 35 million years. If so, then the scientifically determined date for the fossils must be in error. According to the young-earth proponent, the existence of the chitin remnants make sense only if the fossil record stems from a worldwide, catastrophic flood that took place a few thousand years ago, rather than from preserved organism remains millions of years old.1
In many respects, this is not an unreasonable conclusion. Organic compounds are typically rather “delicate” materials that break down readily. Exposure to water, oxygen, bacteria, and enzymes (like chitinases) found in the environment accelerate the compounds’ degradation.
But the chemical stability of organic substances varies considerably. Some organic materials remain remarkably robust—chitin is one of them.
Chitin is a sugar (more specifically, a carbohydrate). Some of the more familiar sugars, such as starch, breakdown quickly. However, other sugars, like cellulose, are extremely durable materials.
Interestingly, chains of glucose molecules make up both starch and cellulose. The key difference between starch and cellulose is the nature of the chemical bond that joins the glucose molecules together. The bond found in starch is called a α-1,4 linkage, while the cellulose bond is called a β-1,4 linkage.
The video below (although a little goofy) provides a good introduction to carbohydrates and the difference between starch and cellulose.
Whether the glucose units are connected via a α-1,4 or a β-1,4 linkage makes all the difference to the sugar’s durability. When joined together with α-1,4 bonds, the linear glucose chains adopt an open helical structure. But if they are bound by a β-1,4 linkage, the chains exist in an extended state. In this latter configuration, the chains also interact with one another via hydrogen bonding, resulting in multiple cross-links between the chains. Multiple chains interact in this way to form a two-dimensional network, or “sheet,” of cellulose chains (figure 1). This large number of cross-links explains cellulose’s robustness.
Figure 1. The structure of cellulose.
Image source: User: Laghi.l (http://en.wikipedia.org/wiki/File:Cellulose_strand.jpg)
Chitin has a similar structure to cellulose, except that its chains are made up of N-acetylglucosamine subunits joined together with β-1,4 linkages (figure 2).
Figure 2. The structure of chitin.
The β-1,4 linkages in chitin give it structural properties and durability similar to those of cellulose, with one exception: the N-acetyl chemical group creates more opportunities for hydrogen bonds to form between chains. This means that the cross-linking in chitin is more extensive than in cellulose, thus, making it even more durable.
Can Chitin Survive for 35 Million Years?
Chitin’s heavily cross-linked structure makes it reasonable to conclude that this molecule could survive for a long period of time. It is not outlandish to think that chitin could persist for 35 million years under the right conditions.
The researchers who discovered the chitin associated with the cuttlefish fossils noted that the molecule was complexed with the mineral aragonite.2 The interaction between aragonite and chitin would have provided additional stability to this already durable organic material.
Furthermore, the researchers noted that the cuttlefish was buried in a low-oxygen environment, which would have prevented the oxidative degradation of the chitin. They also pointed out that the clay and other inorganic materials that buried the cuttlefish would have deactivated the chitinases, thus preventing bacterial degradation.
In other words, chitin’s chemical nature, coupled with the burial and fossilization environment, explains why it survived 35 million years. It is also worth noting that the researchers did observe that some degradation of the chitin had taken place.
The bottom line: The recovery of 35-million-year-old chitin in no way undermines the scientifically determined age of the Earth, nor does it provide any genuine support for young-earth creationism.