Earlier, we wrote about how we can see Earth’s history through the layers of rock we find across the planet today. The notion that ancient cyanobacteria (blue-green algae) were the first to provide the Earth with oxygen may be in for a challenge: a team of scientists led by University of Washington (UW) Earth and Space Sciences doctoral student Jana Meixnerová found that volcanic eruptions may have kickstarted the whole thing by triggering the population explosion of the first cyanobacteria.
The Earth’s atmosphere is perhaps best appreciated in the way it keeps us ventilated. Our planet’s atmosphere consists of about 21% oxygen, but surprisingly enough, it hasn’t always been there. Our young planet’s atmosphere had been filled with elements like nitrogen and hydrogen at that point (due to gases present in the nebula that formed our Solar System, as well as gases brought on by comets impacting our planet during its early phases), but oxygen wouldn’t be spotted until much later. In fact, The first life on Earth may have emerged before any oxygen was ever in our atmosphere. So what happened?
Initially, it was thought that an event referred to as the Great Oxidation Event (GOE) kickstarted oxygen generation in our planet, as cyanobacteria started to photosynthesize the carbon dioxide (CO2) present in our atmosphere and released oxygen as a waste product some 2 to 2.4 billion years ago. This very process is still very much alive today; the job has been primarily passed onto trees and plants, whose leaves contain descendants of those first oxygen producers. Now, with new findings published in the journal Proceedings of the National Academy of Sciences, Meixnerová may have found what triggered these cyanobacteria to appear in large numbers to begin with: ancient volcanic activity.
Back in 2007, an analysis of rocks dated to around the same time as the GOE revealed that there existed a short burst of oxygen activity some 50 to 100 million years before the GOE even started; This one was from study co-author Ariel Anbar, from Arizona State University. Newer explorations into the topic had revealed earlier bursts of oxygen presence in the atmosphere, but no mechanisms had yet been proposed at the time.
Now, the study’s team did a second pass of the rocks from 2007, but instead looked into the presence and concentration of mercury isotopes, or mercury atoms with higher numbers of neutrons than normal. These mercury atoms were associated with large volcanic eruptions, they say, and that their presence in rocks reveal increased volcanic activity in the area. True enough, they found these signatures from mercury isotopes in the rocks from 2007—a few million years before the spikes in oxygen recorded from earlier studies. Study co-author and Earth and Space Sciences professor from UW Roger Buick added that “[the signatures] would most reasonably be explained by volcanic eruptions into the atmosphere.”
To the authors, the presence of volcanic eruptions would mean an abundance of volcanic ash fields—sites with rocks rich in elements like phosphorus. Meixnerová added that the presence of other short-term factors for biological activity, phosphorus “is the one that is most important on long timescales.”
In turn, weathering and rain would release this phosphorus into ancient waterways like rivers, which then feed into the ocean. The presence of phosphorus would, in turn, “fertilize” coastal areas where these waterways and the ocean would meet, making the area prized real estate for the growth of ancient cyanobacteria. Meixnerová continued: “That would have fed microbes that were living in the shallow coastal zones and triggered increased biological productivity that would have created, as a byproduct, an oxygen spike.”
To the authors, their findings may help inform the search for life on other planetary bodies across the cosmos, as geological activity may have more impact on any life evolving on a planet than previously thought. Meixnerová noted: “What has started to become obvious in the past few decades [of research] is there actually are quite a number of connections between the solid, nonliving Earth and the evolution of life.
This connection certainly appears to be true for Earth; the GEO has also been recognized as the initiator for the rapid evolution of multicellular life on Earth.
References
- Biello, D. (2009, August 19). The Origin of Oxygen in Earth’s Atmosphere. Scientific American. Retrieved September 27, 2021, from https://www.scientificamerican.com/article/origin-of-oxygen-in-atmosphere/
- University of Washington. (2021, August 26). Volcanic eruptions may have spurred first ‘whiffs’ of oxygen in Earth’s atmosphere. ScienceDaily. Retrieved September 27, 2021, from https://www.sciencedaily.com/releases/2021/08/210826111724.htm
- University of Zurich. (2013, January 17). Great Oxidation Event: More oxygen through multicellularity. ScienceDaily. Retrieved September 27, 2021, from https://www.sciencedaily.com/releases/2013/01/130117084856.htm
- Warke, M. (2020, June 3). Billions of years ago, the rise of oxygen in Earth’s atmosphere caused a worldwide deep freeze. The Conversation. Retrieved September 27, 2021, from https://theconversation.com/billions-of-years-ago-the-rise-of-oxygen-in-earths-atmosphere-caused-a-worldwide-deep-freeze-139722
- Meixnerová, J., Blum, J. D., Johnson, M. W., Stüeken, E. E., Kipp, M. A., Anbar, A. D., & Buick, R. (2021). Mercury abundance and isotopic composition indicate subaerial volcanism prior to the end-Archean “whiff” of oxygen. Proceedings of the National Academy of Sciences, 118(33). https://doi.org/10.1073/pnas.2107511118
