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Folks, I want you to watch this next clip, because new fossil discoveries have been uncovered.
Let’s learn a little bit more about the Burgess Shale site.
Watch this.
Narrator: Three decades after Darwin’s death, Charles Walcott’s historic work in the Canadian
Rockies did nothing to fill the gaps in the tree of life or the fossil record.
Walcott uncovered the remains of Cambrian animals unknown to Darwin, and each demanded
its own unique progression of evolutionary ancestors, a trail of evidence that did not
exist in the Burgess Shale.
Nelson: Walcott realized that the Cambrian explosion of life was an even bigger problem
than Darwin imagined.
So in an attempt to defend evolution, he reached back to Darwin’s explanation of an incomplete
fossil record.
Meyer: Like Darwin, Walcott thought that the Cambrian explosion was an illusion.
He was convinced that the fossils were there; they were just inaccessible to scientific
discovery.
And he expected that they would eventually be found someplace buried deep beneath the
oceans.
Narrator: For decades Walcott’s hypothesis was widely accepted, but untestable.
However, later in the 20th century, new technologies led to empirical conclusions.
Meyer: Once the oil companies started to drill offshore they brought up what are called drill
cores.
And inside the core were hunks of sedimentary rock, and some of those rocks contained fossils.
But none of them were made by animals that lived before the Cambrian explosion.
Narrator: Since the 1960’s scientists have also used radioactive minerals and evidence
of changes in the earth’s magnetic field to analyze and date undersea sediments.
From extensive surveys, they have created this digital map that defines the age of the
sea floor.
Meyer: We now know that the oldest rocks on the bottom of the sea floor only date back
to the Jurassic period, which means that on the standard geologic timescale they’re
hundreds of millions of years younger than the rocks below the Cambrian strata.
Nelson: If you’re looking for the ancestors to the Cambrian groups, the last place you
would expect to find them is out somewhere on the sea floor.
Those rocks are much too young.
Narrator: So how did the Cambrian animals emerge?
And where are the signs of their evolutionary past?
Darwin and Walcott both confronted and failed to solve this mystery.