September 10, 2009

Study shows evolution of Earth’s animals

Danish-led scientists say an analysis of rock found only in the world's oldest oceans has shed light on how large animals obtained a foothold on Earth.

The team led by University of Copenhagen Professor Robert Frei said it has, for the first time, plotted the rise and fall of oxygen levels in the Earth's atmosphere that occurred during the last 3.8 billion years.

By analyzing the isotopes of chromium in iron-rich sediments formed in the ancient oceans, the team found a rise in atmospheric oxygen levels 580 million years ago was closely followed by the evolution of animal life.

Because animals evolved in the sea, most previous research has focused on oceanic oxygen levels, Newcastle University's Simon Poulton, one of the study's authors, said. Our research confirms for the first time that a rise in atmospheric oxygen was the driving force for oxygenation of the oceans 580 million years ago, and that this was the catalyst for the evolution of large complex animals.

The study that included researchers from Britain and Uruguay appears in the journal Nature.