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Tiny plankton weaken mighty continents

volcano erupting

One researcher believes, the skeletons of tiny organisms could be the trigger for changes in the earth's surface (Source: iStockphoto)

The skeletons of microscopic plankton that flourished billions of years ago may be causing continents to break apart, says a US scientist.

Photosynthetic plankton have been around almost since the planet formed. Perhaps as far back as 3.8 billion years ago, their carbon husks began piling high on the ocean floor as they died.

Over time they became black shales many kilometres thick.

As hundreds of millions of years passed, the shales would become attached to the edges of continents, then slowly kneaded into their interiors.

Today they're prevalent in most major mountain ranges, including the Alps, Himalayas, Sierra Nevada and Appalachians.

Weak areas

Professor Norm Sleep of Stanford University thinks these biologically-built rocks form huge weak areas in the earth's crust.

When plate tectonics begin stretching out a continent these weak areas are the first to break, encouraging the land mass to rip itself apart.

"Black shales sequester radioactive material, so you get areas of high heat and heat flow, which makes the rocks weak," says Sleep.

The effect is just one of many ways Sleep sees living creatures affecting plate tectonics. He'll be presenting the controversial new theory next month at the American Geophysical Meeting in San Francisco.

Volcanic eruptions also owe a debt to biology. Limestone, a rock also formed from the skeletons of ocean-going life, has been subducted into earth's mantle for hundreds of millions of years.

There it heats up until it partially melts, mixes with other magmas and comes boiling up to the surface as lava.

"The composition of Mount Pinatubo and Mount Saint Helens is partly biologically controlled," says Sleep.


Associate Professor Kevin Hefferan of the University of Wisconsin-Stevens Point says parts of Sleep's theory, like radioactivity in black shales, maybe be a bit speculative.

"Some of these things he makes a pretty convincing case for," says Heffernan. "Others, like the radioactive material in shales, are a bit of a stretch. Granites also sequester lots of radioactivity, so why wouldn't they be weak?"

But he adds, "black shales are notorious for landslides, and developing faults. They are inherently weak, so in a way it does make sense that rifting would start with them."