The Rise and Fall of Oxygen

Ancient oceans offer new insight into the origins of animal life

A rise in atmospheric oxygen on the ancient Earth may have ultimately led to the evolution of complex animals.
Credit: Rensselaer Polytechnic Institute

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 led by Professor Robert Frei at the University of Copenhagen in Denmark, and including scientists from Newcastle University, UK, and universities in Uruguay and Southern Denmark, have for the first time managed to plot the rise and fall of oxygen levels in the Earth’s atmosphere over the last 3.8 billion years.


Published in the journal Nature, the data offers new insight into how animal life – and ultimately humans – first came to roam the planet.

"Because animals evolved in the sea, most previous research has focussed on oceanic oxygen levels," explains Newcastle University’s Dr Simon Poulton, one of the authors of the paper.


The study

The evolution of genomic complexity and metabolic pathways during Earth’s history.
Credit: Science


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.


"But instead of this rise being steady and gradual over time, what we saw in our data was a very unstable situation with short-lived episodes of free oxygen in the atmosphere early in Earth’s history, followed by plummeting levels around 2 billion years ago.
