Diamonds pinpoint start of colliding continents

Jewelers abhor diamond impurities, but they are a bonanza for scientists. Safely encased in the super-hard diamond, impurities are unaltered, ancient minerals that can tell the story of Earth's distant past.

Researchers analysed data from the literature of over 4,000 of these mineral inclusions to find that continents started the cycle of breaking apart, drifting, and colliding about 3 billion years ago. The research, published in the 22 July issue of Science, pinpoints when this so-called Wilson cycle began.

Lead author Steven Shirey at the Carnegie Institution's Department of Terrestrial Magnetism explained, ''The Wilson cycle is responsible for the growth of the Earth's continental crust, the continental structures we see today, the opening and closing of ocean basins through time, mountain building, and the distribution of ores and other materials in the crust.

"But when it all began has remained elusive until now. We used the impurities, or inclusions, contained in diamonds, because they are perfect time capsules from great depth beneath the continents. They provide age and chemical information for a span of more than 3.5 billion years that includes the evolution of the atmosphere, the growth of the continental crust, and the beginning of plate tectonics.''

Coauthor and longtime colleague Stephen Richardson of the University of Cape Town added, ''It is astonishing that we can use the smallest mineral grains that can be analysed to reveal the origin of some of Earth's largest geological features.''

The largest diamonds come from cratons, the most ancient formations within continental interiors that have deep mantle roots or keels around which younger continental material gathered.