Tuesday, June 14, 2011

Earliest Examples Of Biomineralization

On Wired Science Brandon Keim summarizes the discovery of phosphatic biomineralization in Neo-Proterozoic protists, published in the June issue of Geology.

The microfossils were preserved in 750 million year old strata of the Fifteenmile Group in Yukon Territory, Canada. This makes it one of the earliest examples in eukaryotes of the ability to precipitate minerals from sea water and use them as structural support or as a protective casing around soft tissue.

In marine organisms, biomineralization has evolved independently many times in different eukaryotic groups. Preserved instances of biomineralization from the Neo-Proterozoic and the earliest Cambrian are of unicellular organisms like protists using mostly phosphatic minerals like apatite. That changed with the evolution of larger complex metazoans by early mid Cambrian times. These creatures preferred calcium carbonate in the form of either aragonite or calcite to build their skeletons.

This might reflect changing sea water chemistry, the increasing saturation of the Cambrian shallow water areas in calcium carbonate and the decreasing availability of phosphorus or it might reflect inherent energy efficiencies in large skeletal construction. Perhaps calcium carbonate molecules are easier to assemble into the larger edifices required than calcium phosphate is..that's just my speculation..

Brandon Keim ends his article quite evocatively:

Of course, predators eventually developed their own biomineralization strategies, as did other algae. Eventually it became ubiquitous in the marine world, to the point where what we now call limestone is simply a composite of microscopic fossil seashells. It’s also the primary ingredient in concrete. Their shells have become our own.

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