The evolution of the first animals may have oxygenated the earth's oceans contrary to the traditional view that a rise in oxygen triggered their development.
New research led by the University of Exeter contests the long held belief that oxygenation of the atmosphere and oceans was a pre-requisite for the evolution of complex life forms.
The study, published today in the leading journal Nature Geoscience, builds on the recent work of scientists in Denmark who found that sponges the first animals to evolve require only small amounts of oxygen.
Professor Tim Lenton of the University of Exeter, who led the new study, said: "There had been enough oxygen in ocean surface waters for over 1.5 billion years before the first animals evolved, but the dark depths of the ocean remained devoid of oxygen. We argue that the evolution of the first animals could have played a key role in the widespread oxygenation of the deep oceans. This in turn may have facilitated the evolution of more complex, mobile animals."
The researchers considered mechanisms by which the deep ocean could have been oxygenated during the Neoproterozoic Era (from 1,000 to 542 million years ago) without requiring an increase in atmospheric oxygen.
Crucial to determining oxygen levels in the deep ocean is the balance of oxygen supply and demand. Demand for oxygen is created by the sinking of dead organic material into the deep ocean. The new study argues that the first animals reduced this supply of organic matter both directly and indirectly.
Sponges feed by pumping water through their bodies, filtering out tiny particles of organic matter from the water, and thus helping oxygenate the shelf seas that they live in. This naturally selects for larger phytoplankton the tiny plants of the ocean which sink faster, also reducing oxygen demand in the water.
By oxygenating more of the bottom waters of shelf seas, the first filter-fe
|Contact: Eleanor Gaskarth|
University of Exeter