Solution to Darwin's dilemma: Discovery of the missing Precambrian record of life

In 1859. in On the Origin of Species, Darwin broached what he regarded to b e the most vexing problem facing his theory of evolution-the lack of a rich fossil record predating the rise of shelly invertebrates that marks the be ginning of the Cambrian Period of geologic time (approximate to 550 million years ago), an "inexplicable" absence that could be "truly urged as a vali d argument" against his all embracing synthesis. For more than 100 years, t he "missing Precambrian history of life" stood out as one of the greatest u nsolved mysteries in natural science. But in recent decades. understanding of life's history has changed markedly as the documented fossil record has been extended seven-fold to some 3,500 million years ago, an age more than three-quarters that of the planet itself. This long-sought solution to Darw in's dilemma was set in motion by a small vanguard of workers who blazed th e trail in the 1950s and 1960s. just as their course was charted by a few p ioneering pathfinders of the previous century, a history of bold pronouncem ents, dashed dreams, search, and final discovery.