Lack of oxygen delayed the appearance of animals on Earth


Share post:

Geologists are letting the air out of a nagging mystery about the development of animal life on Earth. Scientists have long speculated as to why animal species didn’t flourish sooner, once sufficient oxygen covered Earth’s surface. Animals began to prosper at the end of the Proterozoic period, about 800 million years ago — but what about the billion-year stretch before that, when most researchers think there also was plenty of oxygen? Well, it seems the air wasn’t so great then, after all.

Lack of oxygen delayed the appearance of animals on Earth
The photo shows a sample collected in northern China with abundant large grains 
coated by iron oxides. The grains, deposited in shallow, nearshore settings in the 
ancient ocean, can capture the chromium isotope composition of river water draining
 the ancient continents. Those waters, in turn, can record reactions in ancient soil 
in the presence or absence of appreciable atmospheric oxygen. In this way, the iron-rich
 grains are something like an oxygen paleobarometer for the ancient atmosphere 
[Credit: X. Chu, Chinese Academy of Sciences]

In a study published Oct. 30 in Science, Yale researcher Noah Planavsky and his colleagues found that oxygen levels during the “boring billion” period were only 0.1% of what they are today. In other words, Earth’s atmosphere couldn’t have supported a diversity of creatures, no matter what genetic advancements were poised to occur.

“There is no question that genetic and ecological innovation must ultimately be behind the rise of animals, but it is equally unavoidable that animals need a certain level of oxygen,” said Planavsky, co-lead author of the research along with Christopher Reinhard of the Georgia Institute of Technology. “We’re providing the first evidence that oxygen levels were low enough during this period to potentially prevent the rise of animals.”

The scientists found their evidence by analyzing chromium (Cr) isotopes in ancient sediments from China, Australia, Canada, and the United States. Chromium is found in Earth’s continental crust, and chromium oxidation is directly linked to the presence of free oxygen in the atmosphere.

Lack of oxygen delayed the appearance of animals on Earth
Christopher Reinhard and Noah Planavsky conduct research for 
the study in China [Credit: Yale University]

Specifically, the team studied samples deposited in shallow, iron-rich ocean areas, near the shore. They compared their data with other samples taken from younger locales known to have higher levels of oxygen.

Oxygen’s role in controlling the first appearance of animals has long vexed scientists. “We were missing the right approach until now,” Planavsky said. “Chromium gave us the proxy.” Previous estimates put the oxygen level at 40% of today’s conditions during pre-animal times, leaving open the possibility that oxygen was already plentiful enough to support animal life.

In the new study, the researchers acknowledged that oxygen levels were “highly dynamic” in the early atmosphere, with the potential for occasional spikes. However, they said, “It seems clear that there is a first-order difference in the nature of Earth surface Cr cycling” before and after the rise of animals.

“If we are right, our results will really change how people view the origins of animals and other complex life, and their relationships to the co-evolving environment,” said co-author Tim Lyons of the University of California-Riverside. “This could be a game changer.”

“There’s a lot of interest right now in a broader discussion surrounding the role that environmental stability played in the evolution of complex life, and we think our results are a significant contribution to that,” Reinhard said.

Author: Jim Shelton | Source: Yale University [October 31, 2014]



Related articles

Colossal hot cloud envelops colliding galaxies

Scientists have used Chandra to make a detailed study of an enormous cloud of hot gas enveloping two...

Libyans battle to protect ancient treasures

Walking along the tree-lined gravel track towards one of the Roman Empire's greatest architectural legacies, little can prepare...

Melting snow in Norway reveals Iron Age tunic

A boat neck sweater made of warm wool and woven in diamond twill was a dominating fashion trend...

Egyptologists still digging up past, even with uncertain future

The Egyptian Revolution that began a year ago continues to create instability in a country rich with antiquity....

US returns ancient Persian artefact to Iran

On Wednesday, September 25th, the United States returned to Iran an artifact that was seized by Customs enforcement...

Big, shape-shifting animals from the dawn of time

Why did life on Earth change from small to large when it did? Researchers from the University of...

Monarch butterfly numbers drop by 27 percent in Mexico

The number of monarch butterflies wintering in Mexico dropped by 27 percent this year, reversing last year's recovery...

Crossrail project uncovers Bedlam burial ground

Crossrail, Britain's biggest construction project and the biggest archaeological dig in London for years, has uncovered everything from...