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.

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.