Skip to main content

Tracking the History of Early Life on Earth

September 13, 2016

Back in the 19th century, Charles Darwin wondered why he could find no fossil evidence of life that predated the Cambrian Period, 541–485.4 million years ago. He understood that life must have evolved in complexity over millions of years, yet the fossils that appeared at the beginning of the Cambrian Period were surprisingly advanced: macroscopic, multicellular, and diverse in form.

About a hundred years later, in 1953, fossilized microorganisms from a much older period (about 1.9 billion years ago) were finally found in the Gunflint chert on the Canadian shores of Lake Superior, giving scientists a much better picture of how the earliest life evolved. This pre-Cambrian fossil record charts the emergence and diversification of one-celled organisms, the advent of multicellularity and sexual reproduction, and the evolution of macroscopic organisms.

Ross Anderson (Geology and Geophysics), advised by Derek Briggs, studies this early record of life. His search for fossils focuses on the Proterozoic (~2.5–0.5 billion years ago) and has taken him to the deserts of southwest Mongolia, the island of Islay on the west coast of Scotland, and the ranches of western Texas. He studies the diversification of eukaryotic organisms — those whose cells contain a nucleus and other organelles (such as mitochondria and chloroplasts) and are enclosed within a membrane.

In Mongolia and Scotland, Anderson has been part of a collaborative effort through the NASA Astrobiology Institute to document the environment and paleobiology from 750–600 million years ago, when our world was frozen in what Anderson calls “two separate snowball Earth ice ages.” Using Scottish fossils, Anderson has shown that eukaryotic life survived and flourished in coastal ecosystems in the lull between the two glaciations. In Mongolia he has discovered rich microbial communities in rocks that date to just after the second ice age and is working on some that exhibit macroscopic biomineralization almost 50 million years earlier than any previously seen. His Mongolian fossils now represent some of the oldest examples of life held in the collections of the Yale Peabody Museum of Natural History.

Anderson is not just describing newly found records of ancient life; he is actively probing the nature of the fossil record itself. Earlier scientists found little evidence of pre-Cambrian life because fossilization is heavily biased towards organisms with mineralized parts. Soft tissues and entirely soft-bodied organisms (including most microbes) were only preserved in exceptional circumstances that restrained decay. Biomineralization only became widespread immediately prior to the Cambrian Period, so pre-Cambrian organisms rarely formed fossils.

Anderson is at the forefront of research into the conditions conducive to fossilization, investigating in particular the role of clay minerals. According to one theory, they might slow decay by interfering with the biology of degraders; according to another, they might form in-situ on decaying carcasses and protect them. He uses innovative analytical tools to document the minerals associated with fossils on a microscopic scale and has brought a large volume of data to bear on this problem by analyzing rocks containing spectacular fossils from Canada, China, Norway, Mongolia, and the US

Anderson has won awards for his research from ExxonMobil, the Geological Society of America, the Geological Association of Canada, the Geological Society of London, the Palaeontological Association, and the Paleontological Society. He is currently recognized as a NASA Earth and Space Science graduate student fellow.

Before coming to Yale, Anderson grew up in the village of Gotham, near Nottingham, England, and earned his undergraduate degree from Harvard University. He chose Yale for graduate studies because of its rich history of paleontological investigation, superb natural history collections, and the opportunity to work with Derek Briggs. While here, when not searching for or analyzing fossils, he can be found playing golf at the Yale golf course or organizing department field trips.