The formation of the Great Unconformity may have had a hand in this

Apr 23, 2012 07:49 GMT  ·  By
Organisms such as these trilobites were the norm in Earth's oceans before the Cambrian Explosion
   Organisms such as these trilobites were the norm in Earth's oceans before the Cambrian Explosion

A new study, funded by the US National Science Foundation (NSF), provides new data on the Great Unconformity, a geological curiosity that may help explain a phenomenon called the Cambrian Explosion. During this event, life on Earth became extremely diverse.

This increase in diversity occurred somewhat unexpectedly, and the reasons it happened are still shrouded in mystery. Before the Explosion, the planet was mainly populated by soft-bodied creatures living in the oceans. Trilobites were the most common of these simple beings.

This was the norm for a very long time. But things changed about 600 million years ago. Suddenly, a huge diversity of animals began to unravel, which resulted in the creation of all ancestors for all species living today.

The process only lasted for a few tens of millions of years, which is a very brief interval at geological timescales. For comparison, the Earth is 4.5 billion years old. Experts say that life not only diversified, but also experienced a significant increase in complexity.

During the Cambrian Explosions, scientists add, the first shells and skeletons evolved, at a time when multi-cellular organisms also began to spread across the surface of the planet. Geologists now believe they have found a way to explain what happened.

They say that a geological abnormality called the Great Unconformity may help explain this mystery. The abnormality occurs between geological layers made of very old igneous and metamorphic rocks, and sediments that are significantly younger, Astrobiology Magazine reports.

“The Great Unconformity is a very prominent geomorphic surface and there's nothing else like it in the entire rock record,” University of Wisconsin-Madison geoscience professor and study leader, Shanan Peters, explains.

The scientist says that the Unconformity mixes very old rocks that formed inside Earth's crust with young sediments, deposited by shallow seas that covered the continents just 500 million years ago. Details of their work were published in the April 19 issue of the top scientific journal Nature.

“The magnitude of the unconformity is without rival in the rock record. When we pieced that together, we realized that its formation must have had profound implications for ocean chemistry at the time when complex life was just proliferating,” Pomona College expert Robert Gaines says.

“We're proposing a triggering mechanism for the Cambrian explosion. Our hypothesis is that biomineralization evolved as a biogeochemical response to an increased influx of continental weathering products during the last stages in the formation of the Great Unconformity,” Peters adds.

The Great Unconformity “explains a lot of lingering questions in different arenas, including the odd occurrences of many types of sedimentary rocks and a very remarkable style of fossil preservation. And we can't help but think this was very influential for early developing life at the time,” Gaines concludes.