Biologically speaking, it isn't that hard to create very simple, one-celled organisms. But the leap to multicellular life requires many factors to line up just perfectly. Now a new hypothesis suggests we wouldn't even be here without some well-timed erosion.
Certain proteins seem to be essential for the rise of multicellular organisms, and those proteins require ready access to heavy-metal elements like zinc and copper. That's no problem these days, but these heavy-metal elements spent a couple billion years of Earth's early history locked away where organisms couldn't get access to them, and the absence of these elements likely held our earliest ancestors' evolutionary path in stasis, unable to make the big leap to being multicellular.
Exactly where those elements were has long been a big question for geologists, with previous explanations looking at the oxygen-starved ocean depths and ore deposits in the Earth's crust as likely storage sites. But now John Parnell and his team of geoscientists at Scotland's University of Aberdeen have come up with a most intriguing alternative. ScienceNOW has the explanation, but the long and short of it is that we owe granite a massive debt of gratitude:
he essential metals eroded from a rare type of granite that formed in large amounts soon after Earth's landmasses collided to create the supercontinent Nuna, about 1.9 billion years ago. The team's analyses show that most deposits of this variety of granite-whose chemical composition caused the metals to be concentrated in ore deposits that were readily eroded, rather than distributed throughout the rock-formed between 1.8 billion and 1.3 billion years ago, when molten material from deep below Earth's crust rose to just beneath the surface and crystallized. The geological record worldwide contains copious evidence that this form of granite began eroding almost immediately, delivering a variety of metals to coastal and lowland environments, the researchers say.
There's lots of evidence worldwide to fit the researchers' new hypothesis. The supercontinent Nuna seems to have started eroding about 1.9 billion years ago, and vital sulfate minerals start appearing in the geological record about 1.7 billion years ago. It was these minerals, among other raw materials, that helped give one-celled organisms the proteins necessary to jump to multicellular life. For more on this idea and some alternative hypotheses, check out ScienceNOW.
Image by shandchem on Flickr.