“Then something happened.”  Question: are you reading a science article, or a fictional screenplay?  Are you in the Science Department or the Humanities Department?  Are you in the lab or the theater?  Find out in today’s episode of “Explain the Cambrian Explosion.”

The short sentence “Then something happened” appears in a press release from the University of Wisconsin-Madison, entitled, “Great Unconformity: Evidence for a geologic trigger of the Cambrian explosion” (see it also on PhysOrg).  The references to geology, fossils and evidence sure sounds like this is coming from the science lab.  Here’s the context:

The oceans teemed with life 600 million years ago, but the simple, soft-bodied creatures would have been hardly recognizable as the ancestors of nearly all animals on Earth today.

Then something happened. Over several tens of millions of years – a relative blink of an eye in geologic terms – a burst of evolution led to a flurry of diversification and increasing complexity, including the expansion of multicellular organisms and the appearance of the first shells and skeletons.

The results of this Cambrian explosion are well documented in the fossil record, but its cause – why and when it happened, and perhaps why nothing similar has happened since – has been a mystery.

The conflict having been set up, it’s time for the protagonist to enter the stage:

New research shows that the answer may lie in a second geological curiosity – a dramatic boundary, known as the Great Unconformity, between ancient igneous and metamorphic rocks and younger sediments….

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