Metabolism 550 Million Years Ago
An article on early life was published in the journal Nature Communications by recent Earth System Science MS student Lucas Cherry, AOES Assistant Professor Geoffrey Gilleaudeau, and collaborators from other institutions. Starting about 540 million years ago (Ma), the number and complexity of animal species on Earth soared in the Cambrian Explosion. The organisms that evolved into all the distinct phyla seen in the Cambrian lived in the Ediacaran Period (574-539 Ma), the time immediately before. Fossils show multicellular organisms dubbed Rangeomorphs, which may be the progenitors of the later, more complex organisms, including humans.
Much is unknown about Rangeomorphs, including the basic question of how they got their energy. Most modern animals derive their energy from aerobic respiration, which relies on combining oxygen with carbohydrates and other compounds. That’s the reason we breathe and eat. On the other hand, early life emerged before there was much oxygen in Earth’s atmosphere, and so was based on anaerobic metabolisms. Cherry, Gilleaudeau, and co-authors’ paper “A diverse Ediacara assemblage under low-oxygen conditions” reports on their test of whether the Rangeomorphs were aerobic or anaerobic. They correlated Rangeomorph fossils with their environment by studying carbonates in arctic Siberia that were deposited when the site was in the ocean. By studying the isotopic and elemental composition of the formations in which the fossils were found, they were able to determine that the Rangeomorphs lived “in environments that were often anoxic” (without oxygen). Though the atmosphere was already oxygenated by the Ediacaran, Cherry et al., as well as work by others, indicates that it was not just this particular site that was anoxic, but much of the coastal and deep ocean.
The widespread anoxic environment suggests that Rangeomorphs had an anaerobic metabolism, though it’s also possible that the fossils date from [geologically] brief periods of oxygenation that were too short to show up in the sedimentary record that Cherry et al. analyzed. Overall, these data shed important new light on the basic biology and ecology of the earliest macroscopic life on Earth.
Lucas Cherry has graduated from George Mason and is now working as an environmental consultant for Ramboll in Arlington, VA. Dr. Gilleaudeau teaches about the long sweep of the Earth’s story in GEOL 441/541 Great Events in Earth History, next offered in Spring 2023.