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hydrogen, oxygen, nitrogen, sulfur, phosphorus], to monomers, to polymers, to cells; we know that the origin of life was early, microbial, and unicellular; and we know that an RNA world preceded today’s DNA-protein world. We do not know the precise environments of the early earth in which these events occurred; we do not know the exact chemistry of some of the important chemical reactions that led to life; and we do not have any knowledge of life in a pre-RNA world.” As for what we have failed to consider, Schopf suggested that the “‘pull of the present’ makes it extremely difficult for us to model the early earth’s atmosphere and the biochemistry of early life.”

Later, Lynn Margulis, in her inimitable rapid-fire style, hit Lazcano with a point-blank question: “In your opinion, what came first, cells or the RNA world?” Lazcano answered: “If you define a cell as a membrane-enclosed system, then lipids-enclosed systems assisted in the polymerization of molecules, which led to RNA.” Cells first, replicators second.

What Caused the Cambrian

“Explosion” of Life?

One of the creationists’ favorite tactics is to focus on gaps in the fossil record, and there is no bigger gap, they claim, than the so-called “Cambrian explosion,” a geologic period starting around 540 million years ago during which many of life’s major taxa first made their appearance in the fossil record. Intelligent Design theorist Stephen Meyer portrays this “explosion” as a single and instantaneous event, rather than the reality of its development over a fifteen- to twenty-million-year period. (Paleontologists usually modify their description of the Cambrian “explosion” by noting that this is a “geological” moment that, by comparison to biological or human time, is glacially slow.) In fact, Meyer’s paper challenging the standard evolutionary model of the Cambrian explosion was the first creationist paper ever published in a peer-reviewed scientific journal, and creationists have made much of that fact.4

Too bad Meyer was not present when Mikhail Fedonkin, head of the Laboratory of Precambrian Organisms at the Paleontological Institute in Moscow, reviewed the evidence for evolution in the billions of years preceding the Cambrian period. Fedonkin suggests that a fall of global temperatures, and the oxygenation of the biosphere caused by photosynthesis, played major roles in the dramatic change in the availability of heavy metals that he believes were crucial in the metabolic processes that led to the evolution of complex life. This metal-rich environment served as a catalyst: “Over 70 percent of known enzymes contain metal ions as a cofactor of an active site. Fast catalyzed reactions segregated life first dynamically and then structurally from the mineral realm.” Once simple prokaryote cells gave rise to complex eukaryote cells, life was off and running, resulting quite naturally in the Cambrian eruption of complex hard-bodied organisms.

Commenting on Fedonkin’s findings, Stefan Bengtson from the Swedish Museum of Natural History asked, “Why did the build-up to the Cambrian ‘explosion’ take so long?” Noting that 99.99999 percent of all species that ever lived have gone extinct, Bengtson answered his own question: “We do not know because we have nothing else to go on. Life is an evolutionary bush, not an evolutionary tree, but our data based on extant life induce us to prune the bush into a tree, so we need more data.”

What Causes Major Shifts in Evolution?

Richard Fortey from the British Museum of Natural History investigates the importance of mass extinction events in resetting the direction of evolution, the magnitude of evolutionary arms races in driving morphological innovation, the relationship of climate change to evolutionary change, and the extent to which evolution can be described as directional. With half a billion years of a rich fossil record, Fortey said, we can track evolutionary periods of creativity and crises. Stephen Jay Gould’s 1989 book Wonderful Life stimulated a lot of new ideas about the Cambrian explosion of life’s diversity,