Associate Professor of Earth Sciences Justin Strauss helped lead a two-week expedition this summer to one of the most rugged and remote parts of Canada in search of what could prove to be the earliest record of animal life on Earth.
After flying by helicopter to the field site in the Mackenzie Mountains—near the border of the Northwest Territories and Yukon—Strauss and his fellow researchers trekked along the slopes of 7,000-foot peaks examining immense exposed bands of fossilized reefs. Once the bottom of an ancient sea, the mountains—now part of the northern Canadian Rockies—were raised by the collision of Earth’s plates over hundreds of millions of years.
The project is funded by the National Science Foundation and co-led by Akshay Mehra, an assistant professor of earth sciences at the University of Washington who was a Neukom Postdoctoral Fellow in Strauss’ group at Dartmouth, and Phoebe Cohen, professor of geosciences at Williams College. The team includes postdoctoral researchers and graduate and undergraduate students, along with visiting researchers from the University of Oxford.
The researchers collected fossils of what are potentially early multicellular sponges that emerged within reefs formed predominantly by single-celled microbes roughly 850 million years ago.
If confirmed as sponges, the fossils would be the earliest record of animal life by about 200 million years, surpassing multiple examples of unambiguous sponge fossils that appeared later.
Photographer Robert Gill traveled with the team in early August to document their work in the Northwest Territories, which took place with the permission of the Sahtú Dene First Nations communities.
The lead researchers and their students have since begun processing their samples. Strauss is establishing the age of the reefs by uranium-lead and rhenium-osmium radiometric dating, in which the decay of radioactive isotopes can be used as a kind of ancient clock.
Mehra’s group is analyzing thin, polished samples of the reef to look for sponge fossils, as well as conducting microscale grinding to generate 3D reconstructions of the putative sponges and processing drone footage from the Mackenzie Mountains to recreate the reefs in 3D.
Cohen and collaborator Ross Anderson from Oxford are preparing samples for micropaleontology, wherein host rock minerals are dissolved to look for organic residues and microscopic fossils.
The researchers plan to return to the Mackenzie Mountains next summer.