Life of the Oceans - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 149

creatures arose, actively walking or crawling on or burrowing through
the sea floor, and helping to mix oxygen into it. Others ascended into
the plankton, being swept along by (and helping to stir) the ocean
waters. These made bodies and skeletons of carbon, nitrogen, phos-
phorus, and calcium, and so held a significant part of the ocean chem-
istry in their bodies. Other creatures, the corals and algae, would
eventually build monumental constructions—the reefs—on parts of
the sea floor, hotspots of biodiversity that could last for millions of
years and lock away billions of tonnes of carbon within them.
Fossils represent a tiny fraction of the organisms that have lived in
the Earth's oceans, and of these the vast majority only preserve the
hard skeletons. The soft tissues—the eyes, brains, muscles, and inter-
nal organs—rot away quickly. Even more recalcitrant tissues, like
cartilage, have a relatively short shelf life after death. Only rarely do
the soft tissues become preserved, but in an almost perverse but illu-
minating act of nature many of these very rare fossils occur in rocks
of Cambrian age. We probably know more about the soft-bodied ani-
mals that lived in the oceans of the 500 million-year-old Cambrian
Period than we know about life in the oceans of, say, the much more
recent Miocene Epoch, just 25 million years ago. In those ancient
Cambrian fossil-bearing rocks, some of those first animals have pre-
served the soft bodies almost intact. Chief among the sites with soft
body preservation is the fossil fauna of Chengjiang, named after the
small provincial county in southern Yunnan Province, south China.
Cambrian fossils had been known from Yunnan since the early
part of the twentieth century, when the self-trained French palaeon-
tologist Henri Mansuy passed through the region in 1903 to 1904. His
survey was not entirely academic, as the French authorities in Hanoi
wished to extend their influence into China by building a railway to
Kunming. Nevertheless, Mansuy was able to collect a number of fos-
sils, including trilobites, which suggested the rocks here would supply