A colorful tale of feathers: copper remnants in fossilized birds

A recent article at the Institute for Creation Research (ICR), entitled Trace Metals Study Confirms Fossil Has Original Feathers, represents the latest in a series of misguided attacks on conventional fossil ages, which appeal to biochemical remnants as evidence for recent burial. Author Brian Thomas renewed the case in response to a rather ingenious and novel analytical method applied to an Early Cretaceous (~120 Ma), fossilized bird. Researchers at the University of Manchester used synchotron x-ray technology to map out trace metals in the avian fossil—namely copper and calcium, which are abundant in feathers and bones, respectively. The resulting image clearly shows the original distribution of hard and soft biological components. But what do the data actually reflect?Have you ever looked at an artist’s rendition of an ancient species (dinosaur, bird, etc.) and wondered how they pick colors for the skin and feathers? In many cases, the choice is educated guesswork—an artist’s touch. But the researchers in this study employed a more scientific approach. The pigments in bird feathers contain organometallic compounds—essentially a carbon-based structure that binds to a specific metal. Hemaglobin in your blood, for example, is an organic compound that binds to iron so as to color the blood red. Using x-ray analysis to determine the coordination chemistry of trace copper in fossilized feathers, the researchers concluded that the copper derived from a dark pigment called eumelanin. By mapping out where copper is concentrated in the fossil, they inferred that the bird (Confuciusornis sanctus) had dark-brown body feathers, and relatively light-colored wings.The title of Mr. Thomas’s article is very misleading on this point. The Early Cretaceous fossil does not contain original feathers—not even close. All that is left are traces of copper, bound up by singular molecules of cyclic chelates, and a carbonized imprint where the feathers’ organic components decayed long ago into the rock. Instead, Wogelius et al. (2011) argued that the organometallic compounds “most likely derived from original eumelanin,” indicating that even the pigments have all broken down. When this occurred, the eumelanin released the copper chelates, which are now bound up in the mineral lattices of the rock and very well protected from the elements.

The researchers demonstrated the ubiquitous presence of eumelanin-derived copper chelates in other well preserved, avian fossils—both older and younger than the famed Confuciusornis sanctus. They concluded that “trace element chemistry provides a robust and consistent method for identifying pigment because metal zoning may be preserved long after melanosome structures have been destroyed.” In other words, copper chelates naturally break down over time, releasing copper ions into the rock. Copper is not very mobile, however, and binds strongly to oxides, hydroxides, carbonates, etc. Thus the distribution of inorganic copper minerals in fossilized feathers should still reflect that of the original feathers, long after organometallic compounds have all broken down (as in one of the samples).

How did these compounds survive some 120 million years of burial? The findings of Wogelius et al. (2011) are impressive, to be sure (that’s why they were published in Science), but scientists have long used remnants of ancient biochemicals to interpret the history of life. Most commonly, these biomarkers are extracted from kerogen and hydrocarbons (oil/gas), which contain numerous fragments of ancient biomolecules. Either way, the stability of organic molecules highly depends on the environment in which they are stored. Organometallic compounds—like the copper chelates described in this study—are most stable in reducing (low-oxygen), non-acidic environments, where the temperature remains moderately low. Given that these compounds would have seen very little interaction with fluids after burial, it is reasonable to expect that some would survive until today.

The verdict?

Mr. Thomas’s statement that “the original organic molecules have hardly decayed” is simply false. Nearly all organic molecules have since disappeared, or were reduced to a carbon residue that now stains the rock. He goes on to infer that “fissile organic molecules had not been altered into more resistant chemicals”, yet the fissile eumelanin (a carboxylic-acid polymer) is no longer present—only the relatively stable copper chelates.

Arguing from ignorant conjecture, Mr. Thomas adds: “[After] only half a million years…copper should now appear randomly distributed among the rocks, having naturally diffused into the surroundings.” How he determines this timeframe is unstated, but it is inaccurate nonetheless. Geological systems cannot be described by such a broad generalization. In sedimentary strata where the water-rock interaction is high, or acidic groundwater prevails, his statement would almost be true. But these conditions hardly describe that of the Cretaceous and Eocene fossils, which accumulated in anoxic lake bottoms, and whose sediments are interbedded with ashfall—a low-permeability barrier to meteoric water.

Contrary to Mr. Thomas’s enthusiastic review, the modern condition of these fossils is inconsistent with a recent burial (some 4,500 years ago, according to Mr. Thomas). If that were the case, we should find significantly more organic material, as in Quaternary fossils that Mr. Thomas would claim were buried within hundreds of years of the Flood (say, 4,000 years ago?). Not only do the recent findings by Wogelius et al. (2011) corroborate the conventional geological story, but they thoroughly falsify Mr. Thomas’s position.*

*Don’t forget to check out the artist’s rendition of Confuciusornis sanctus at the Audubon Magazine blog, which also contains a helpful overview of the publication in Science.

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