Geologists Provide New Evidence for Reason Behind Rise of Life in Cambrian Period

Dec 07, 2006

Geologists have uncovered evidence in the oil fields of Oman that explains how Earth could suddenly have changed 540 million years ago to favor the evolution of the single-celled life forms to the multicellular forms we know today.

Reporting in the December 7 issue of the journal Nature, researchers from MIT, the California Institute of Technology, and Indiana University show that there was a sudden change in the oxygenation of the world's oceans at the time just before the "Cambrian explosion," one of the most significant adaptative radiations in the history of life. With a increased availability of oxygen, the team speculates, single-celled life forms that had dominated the planet for the previous three billion years were able to evolve into the diverse metazoan phyla that still characterize life on Earth.

"The presence of oxygen on Earth is the best indicator of life," says coauthor John Grotzinger, the Fletcher Jones Professor of Geology at Caltech and an authority on sedimentary geology. "But it wasn't always that way. The history of oxygen begins about two and a half billion years ago and occurs in a series of steps. The last step is the subject of this paper."

The key insight was derived when Grotzinger's student Dave Fike, who is lead author of the paper, analyzed core samples and drillings taken at a depth of about three kilometers from oil wells in Oman, which are known to have the oldest commercially viable oil on the planet. The results of carbon and sulfur isotopic analyses from the material led the team to the conclusion that the oceanic conditions that laid down the deposits originally in Oman were quite different from conditions of today.

"You need a very different ocean for these conditions to exist--more like the Black Sea of today, with an upper oxidized layer and lower reduced layer with very little oxygen," says Grotzinger. "The ocean today is pretty well oxidized at all layers, but the ocean before the Cambrian period must have been very different."

When organic matter falls into an ocean that doesn't stir, it becomes deprived of sufficient oxygen and cannot survive as multicellular forms. For this reason, with a limited amount of oxygen, life continued in its single-celled form for the first three billion years.

But about 550 million years ago, according to the team's geologic evidence, the deep oxygen began mixing its contents with the shallow ocean, resulting for the first time in a fully oxidized deep ocean.

Characterizing the study as paleoceanography, Grotzinger says the evidence is persuasive because it is so clearly evident in the rock record. Geologists have long believed that the rise of oxygen was a key element involved in the Cambrian radiation, so this discovery really helps solidify that hypothesis.

The oxygen trigger helps account for how life 500 million years ago could have gone from its single-celled existence to the emergence just 10 to 15 million years later of all the metazoan phyla we know today. In short, an abrupt increase in the availability of oxygen may have led to the diversity and complexity of life.

Fike is a graduate student at MIT who is currently in residence at Caltech to work with his professor, Grotzinger, who himself came to Caltech from MIT last year. The other authors of the paper are Lisa Pratt of Indiana University and Roger Summons of MIT.

Source: Caltech

Explore further: Improving forecasts for rain-on-snow flooding

add to favorites email to friend print save as pdf

Related Stories

The RV Investigator's role in marine science

9 hours ago

We know more about the surface of the moon than we do about our deepest oceans, and only 12% of the ocean floor within Australia's Exclusive Economic Zone has so far been mapped.

How was the Earth formed?

Dec 10, 2014

Just how did the Earth—our home and the place where life as we know it evolved—come to be created in the first place? In some fiery furnace atop a great mountain? On some divine forge with the hammer ...

Extreme shrimp may hold clues to alien life

Nov 24, 2014

(Phys.org) —At one of the world's deepest undersea hydrothermal vents, tiny shrimp are piled on top of each other, layer upon layer, crawling on rock chimneys that spew hot water. Bacteria, inside the shrimps' ...

Recommended for you

Improving forecasts for rain-on-snow flooding

1 hour ago

Many of the worst West Coast winter floods pack a double punch. Heavy rains and melting snow wash down the mountains together to breach riverbanks, wash out roads and flood buildings.

The Greenland Ice Sheet: Now in HD

2 hours ago

The Greenland Ice Sheet is ready for its close-up. The highest-resolution satellite images ever taken of that region are making their debut. And while each individual pixel represents only one moment in time, ...

NOAA/NASA satellite sees holiday lights brighten cities

20 hours ago

Even from space, holidays shine bright. With a new look at daily data from the NOAA/NASA Suomi National Polar-orbiting Partnership (Suomi NPP) satellite, a NASA scientist and colleagues have identified how ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.