President's Dream Colloquium on Emergence and Complexity of Life

Lecture Abstract

In 1859, in his great work On the Origin of Species, Darwin stated the problem:

“If the theory [of evolution] be true, it is indisputable that before the lowest Cambrian stratum was deposited, long periods elapsed … and the world swarmed with living creatures.  [However] to the question why we do not find rich fossiliferous deposits belonging to these earliest periods … I can give no satisfactory answer. The case at present must remain inexplicable; and may be truly urged as a valid argument against the views here entertained.”

For more than 100 years, this missing record of the earliest chapters in life’s long history stood out as among the greatest unsolved questions in all of natural science. 

In Darwin’s day, the oldest fossils were trilobites, lobster-like animals entombed in Cambrian-age rocks (known now to date from about 550 million years ago). However, in the mid-1960s, understanding of the early history of life began to change as new finds — not of animals, but of tiny microscopic microbes — extended the fossil record into the remote reaches of geological time. 

Today, life on Earth is known to have emerged at least as early as 3,500 million years ago, some seven times earlier than was known to Darwin or to scientists even a few decades ago.  Indeed, current techniques provide the means to image such ancient fossils in cell-by-cell detail — fully, in three dimensions, even though they are completely embedded inside rocks — and to analyze both their cellular form and their organic, coaly, composition.  

Recently, these new techniques have provided ways to document an ancient sulfur-cycling anaerobic ecosystem, not previously known from the geological record, and microscopic fossils petrified in gypsum, a rock-type generally thought by paleontologists to be barren of fossils that is widespread on Mars. 

Darwin was right — the Precambrian world did, indeed, “swarm with living creatures.” The dilemma he posed about the “missing” early record of life has been resolved.  And the ancient fossils that have been discovered, and their relevance to the search for life on other planets, would have pleased him enormously.