Charles Darwin cautioned against this interpretation, writing in On the Origin of Species that, “We should not forget that only a small portion of the world is known with accuracy.” He saw the entire geologic record as a history book stretching across multiple volumes. “Of this history we possess the last volume alone, relating only to two or three countries,” he wrote. “Of this volume, only here and there a short chapter has been preserved; and of each page, only here and there a few lines.”
The truth, it now seems clear, is that Precambrian animals had existed in great numbers but, being soft-bodied, had not lent themselves to fossilization. They crop up exceedingly rarely, in places like Mistaken Point, where the geologic conditions were just right.
Conquerors and Demons
Liu’s plan was to begin our tour at a prominent fossil site called Pigeon Cove, and then work our way forward in time, covering about 10 miles on foot and by car. We would visit each of the area’s most impressive fossil beds, culminating at the surface where Liu had discovered the fossil trails.
Windows open to the hard sea wind, we raced across a landscape of stooped trees and yellowing grass to Pigeon Cove, where we got out and hiked down a dirt path to the seaside. There lay a flat slab of rock, the size and texture of three cracked concrete tennis courts, which sloped down into the sea. Its surface was a swirl of gray, chalkboard green and dusty eggplant. Impressed into it were faint but distinct symbols. One looked like a fleshy frond. Another looked like an arrowhead, but in life probably resembled one of those conical corn snacks sold at gas stations, with its narrow end stuck into the ground. A third, which paleontologists call a “pizza disc,” was just a big, bubbly mess.
A few hours later, we made our way over to the area’s most famous fossil bed, the blandly named E Surface, which cantilevers out high over the ocean. Before we stepped out onto the bedding plane, we removed our shoes and put on polyester booties to protect the fossils from erosion.
The Pigeon Cove surface had held about 50 fossils; E Surface held 4,000. They were everywhere, a vast fossilized garden of fronds and blobs and spirals, some bigger than a large hand. Of course, it was not an actual garden; plants would not appear in the fossil record for another 200 million years. For some reason, I was stuck on this point. They looked like plants, I kept saying.
Oxford postdoc Jack Matthews, the youngest member of Liu’s research group, explained that this was because, this far in the past, the lines between the kingdoms grow fuzzy. We, and every organism currently living on Earth, he said, are at the crown of the tree of life. Down at the base of the tree lie the very first single-celled organisms, from which everything else sprang. So the further down the trunk of the evolutionary tree you look, the more organisms resemble one another.
“That’s when you get into the nitty-gritty definitions of what defines, say, an animal and a fungus,” Matthews said. “They’re actually biologically really close, but they just ‘decide’ to stick their cells together slightly differently. And just because one evolved to stick its cells together differently than another, one mainly just grows on dead trees, and the other has conquered the Earth.”