Massive Geographic Shift May Have Caused Ancient Explosion of Life During the Cambrian

Scientists may have solved the riddle of the "Cambrian explosion" after analyzing geologic history. They've found that that rapid diversification of animal life that occurred 530 million years ago could possibly be the result of a major tectonic event.

The Cambrian explosion is one of the most significant events in Earth's history. This surge of evolution led to the appearance of almost all modern animal groups, and occurred over a relatively short period of time.

"At the boundary between the Precambrian and Cambrian periods, something big happened tectonically that triggered the spreading of shallow ocean water across the continents, which is clearly tied in time and space to the sudden explosion of multicellular, hard-shelled life on this planet," said Ian Dalziel, one of the researchers, in a news release.

Previous studies suggested that during the early Cambrian, the ancient continent of Laurentia, which is the ancestral core of North America, had already separated from the supercontinent of Gondwanaland. Yet in this study, the scientists propose that present-day North America was still attached to the southern continents until at some point into the Cambrian period.

The development of a deep oceanic gateway between the Pacific and Iapetus, which is the ancient Atlantic, oceans isolated Laurentia in the early Cambiran. This would have caused global sea level rise and an explosion of life.

"The reason that people didn't make this connection before was because they hadn't looked at all the rock records on the different present-day continents," said Dalziel.

As the sea levels rose, the ancient geologic and geographic changes probably led to a buildup of oxygen in the atmosphere and a change in ocean chemistry. This, in turn, allowed more complex life forms to evolve over time.

"I'm not claiming this is the ultimate explanation of the Cambrian explosion," said Dalziel. "But it may help to explain what was happening at that time."

The findings are published in the journal Geology.