North scientists delve into the start of life

Sep 12 2009 by Tony Henderson, The Journal

ANCIENT oceans are offering an insight into the origins of animal life in a study involving Newcastle University experts.

Analysis of a rock type found only in the world’s oldest oceans has shed new light on how large animals first got a foothold on the Earth.

A scientific team has for the first time plotted the rise and fall of oxygen levels in the Earth’s atmosphere over the last 3.8 billion years.

By analysing the isotopes of chromium in iron-rich sediments formed in the ancient oceans, the team has found that 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 focussed on oceanic oxygen levels,” said Newcastle University’s Dr Simon Poulton.

“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.”

Distinctive chromium isotope signals occur when rocks are altered and weathered as a result of oxygen levels rising in the atmosphere.

The chromium released by this weathering is then washed into the seas and deposited in the deepest oceans – trapped in iron-rich rocks on the sea bed.

Using this new data, the research team has not only been able to establish the trigger for the evolution of animals, but have also demonstrated that oxygen began to pulse into the atmosphere earlier than previously thought.

“Oxygen levels actually began to rise 2.8 billion years ago,” said Dr Poulton.