By Dr. Jennifer Glass and Matt Barr
Now that we’ve laid a foundation for microbial activity early in Earth’s history, we will start discussing some of the exciting research going on at Georgia Tech in the School of Earth and Atmospheric Sciences (EAS).
For over three-fourths of Earth’s history, its ocean chemistry was vastly different than it is today. Instead of today’s “anemic” (iron-starved) oceans, the ancient oceans were “ferruginous”, containing low oxygen and abundant iron. By studying modern ecosystems that still retain ferruginous habitats, “geobiologists” at GT EAS and around the world are probing questions about how microbial life flourished and changed the face of the early Earth.
Dr. Jennifer Glass’ research group is at the forefront of studying interactions between microbes, iron and greenhouse gases. In addition to carbon dioxide, two other important greenhouse gases are methane and nitrous oxide, both of which likely warmed our planet enough to enable the persistence of liquid water and evolution of early life billions of years ago, despite the faint young sun paradox discussed in our previous post.
The Glass lab is studying greenhouse gas cycling via microbial and abiotic redox reactions, which move electrons between chemicals towards a state of lower free energy, and are crucial for all life. These redox reactions are also key to nutrient cycles that move bioessential elements like carbon, nitrogen and iron through planetary ecosystems. Half the lab works on methane, and the other half on nitrous oxide, with iron as a common theme connecting the two.
Methane is the second most abundant greenhouse gas on modern Earth and may have been even more important in our planet’s past. With funding from NASA’s Exobiology and Evolutionary Biology Program, the Glass lab and its collaborators are testing the hypothesis that iron and methane contributed to early metabolic processes of primitive – yet completely unknown – microbes that likely still exist today in ferruginous ecosystems. These microbes might “breathe” iron and “eat” methane to obtain energy and food.
Lake Matano in Indonesia is one of the best analogs that exists today of ferruginous oceans that existed in the Archean Eon. While most lakes turn over at least once a year, Lake Matano’s deep waters are too dense to mix with its surface waters. This means that the mud at the bottom of Lake Matano is completely shielded from atmospheric oxygen and is constantly bathed with iron from mineral-rich soils flanking the lake. Consequently, it may harbor microbial communities similar to those in the Archean oceans. Collaborator Dr. Sean Crowe of the University of British Columbia, an adjunct professor in EAS, has provided the Glass lab with sediment samples from a variety of depths in this ecosystem.
Glass lab PhD candidate Marcus Bray and postdoc Dr. Nadia Szeinbaum are cultivating microbes from these precious sediments to decipher how their ancient relatives were able to grow without oxygen in Earth’s deep past. They exposed these microbes to metal-rich minerals and methane and then waited patiently while both substrates were slowly transformed. They’ve also teamed up with the lab of Dr. Frank Stewart (GT Biology) to sequence the microbes’ DNA to study how the microbial population has changed over time. The longest enrichments have been running for over two and a half years, and certain microbial groups that started off as minor players are now dominating. Ongoing work aims to show precisely how these microbes are thriving off of methane and metals. By understanding the influence of iron on methane, and vice versa, the mechanisms controlling methane flux to Earth’s atmosphere can be better resolved, both in the modern and the Archean eras. This research could simultaneously unlock ancient mysteries and potentially provide solutions for a greener future.
I caught up with Chloe Stanton, an undergraduate EAS major who has worked in the Glass lab since her first semester on campus, to learn more about another project, funded by the NASA Astrobiology Institute’s “Alternative Earths” team. Chloe, EAS PhD candidate Amanda Cavazos, and Dr. Glass are investigating the production of nitrous oxide (also known as “Laughing Gas”) via chemical interactions between iron and reactive nitrogen-containing molecules. Chloe showed me how she carefully concocts small batches of the poisonous gas nitric oxide in a chemical fume hood and makes artificial iron-free seawater from scratch by dissolving individual salts in pure water. She then measures rates of nitrous oxide production from these primitive substrates in an anoxic chamber that mimics the Earth’s ancient oxygen-free atmosphere, with the goal of determining how fast these reactions occurred in the “middle Earth”, or Proterozoic Eon.
These two research projects underway in the Glass lab open up some intriguing possibilities. Aside from giving us a better understanding of how the Earth has stayed habitable for microbes over billions of years, this research might be useful to environmental engineering efforts that employ microbes to treat waste water and cut greenhouse gas emissions. Also, the very existence of these microbes greatly broadens the spectrum of conditions under which we know life can develop. Unique assemblages of gas molecules could even be used as “biosignatures” for life on exoplanets outside of our solar system, with significant implications for astrobiology’s search for life elsewhere in the cosmos and new exploration avenues in future space missions.
Thanks for reading, and stay tuned for next week’s journey into science at GT EAS!