Yellowstone National Park is famous for its hot springs, geysers, wildlife, and incredible geology. While the area is popular among visitors every year, scientists are also excited about the hot springs at this site as they create unique habitats for life. Surprisingly, this national park’s hot springs may hold clues to what conditions may have been like on Earth between 2 to 4 billion years ago. The temperatures of some hot springs at Yellowstone (up to the boiling point of water, 100°C) allow only certain organisms to flourish, as only the fittest can survive. In other words, microorganisms (algae, bacteria, fungi, archaea) living there need some essential adaptations. It turns out, these organisms that thrive in and around Yellowstone’s hot springs may be very similar to the organisms that survived and thrived on the early Earth.
Earth before 2.5 billion years ago looked a lot different than it does today. Oxygen was scarce in the atmosphere, and the ozone layer, the layer that protects us from the sun’s harmful UV radiation, had yet to form. Any life during this time would need a good survival strategy to shield itself from radiation. This could be in the form of a pigment, a pool of water, or a shield made of minerals. Microbes in hot springs similar to Yellowstone’s could have used silica, a mineral that forms from the hot spring fluids, as a shield to protect themselves.
In this study, researchers at the University of Minnesota wanted to know if photosynthetic (sunlight-using, oxygen-producing) microorganisms in these Yellowstone springs and those living underneath silica near the springs were alive and active.
Using a technique called 16S and 18S rRNA gene sequencing, they identified organisms living in 3 locations. These locations included the area next to hot springs but just below silica, organisms living at the surface, and the organisms living fully submerged in hot springs. At all three places, they found an abundance of cyanobacteria and algae, two groups that are known to make oxygen through photosynthesis. To better understand how productive these organisms were at these three sites, the researchers tracked carbon uptake through photosynthesis by adding sample from each location plus a small amount of a labeled carbon compound to airtight jars. They then monitored how much labeled compound was used over time.
From this, they found that photosynthetic microorganisms living beneath the silica here can be just as productive as those living in the hot springs or those living on top of the silica. This was remarkable because the amount of land covered by this silica is much larger than the other two areas. So, this previously ignored habitat could actually be a major source of primary oxygen production.
Thinking back to the early Earth billions of years ago, these protective layers of silica may have helped to sustain any life living just below them. The oxygen produced from photosynthetic organisms living there could have created local “islands” of oxygen in a world otherwise without it. These small microorganisms may have helped to spark the rise of oxygen, and in turn the rise of more complex life on Earth.