UNITED STATES: Scientists have discovered that the earliest life on Earth may have been underwater, where it would have been protected from the sun’s deadly ultraviolet rays, by researching the genetic tree of life.
Scientists are slowly piecing together genetic puzzle pieces to understand how the first life on Earth, which existed between 2.5 and 4 billion years ago, lived. However, the origin of life on Earth is still a mystery.
Researchers from the Universities of Wisconsin-Madison and California-Riverside have now utilised machine learning to reconstruct the evolutionary history of the protein-based chemical rhodopsin, going all the way back to the earliest known microbial life forms on Earth. The scientists contend that the findings might potentially help the hunt for life in space.
The new study’s co-author and astrobiologist Edward Schwieterman of the University of California Riverside described it as “like taking the DNA of numerous grandkids to duplicate the DNA of their grandparents” in a statement.
Scientists believe that rhodopsin served as the early life’s battery by converting sunlight into energy. Rhodopsin can absorb blue, green, yellow, and orange light on the current Earth. The light-absorbing rods and cones our eyes employ to see the outside world are also distantly related to this.
To find the genes that control rhodopsin throughout the broadest possible range of Earth’s life, Schwieterman and his colleagues first used machine learning to find those genes. They then determined which genes had the most extended lineages.
According to this study, the only blue and green light was absorbed by ancient rhodopsin. In a scenario where early life may have evolved in the ocean, where blue and green wavelengths of light penetrate deeper into a column of water than other optical wavelengths, this reduced capability makes sense. In this scenario, the ability to absorb these wavelengths to produce energy would have been crucial.
Since a large portion of the planet’s surface would have been hostile to life, the ocean may have been one of the few sites where early life might have developed safely. This is because no ozone layer shields the early Earth from dangerous solar UV radiation.
After all, there was no free oxygen in the atmosphere. Instead, life would have taken refuge underground or at the bottom of the ocean, away from the harmful ultraviolet rays.
As a result, the discoveries help us understand the environment that prehistoric life on Earth lived in and how it derived energy from that environment.
According to the primary author of the study Betul Kacar, an astrobiologist at the University of Wisconsin-Madison, “We revived ancient DNA sequences of one molecule, and it allowed us to link to the biology and environment of the past.”
Energy “may have been quite rare on early Earth,” Schwieterman speculated, adding that prehistoric bacteria had to have learned to utilise what energy was available without sophisticated processes like photosynthesis, which contemporary plants employ to convert sunlight into energy-storing molecules.
Rhodopsin is not linked to chlorophyll, the substance responsible for photosynthesis, even though they function similarly. Each would have instead evolved independently to occupy the ecological niche left vacant by the other.
In what is known as the Great Oxidation Event, oxygen created by microscopic photosynthetic cyanobacteria suddenly inundated Earth’s atmosphere, starting the evolution of rhodopsin into its more contemporary form. Because many microbiological species that didn’t breathe oxygen perished due to the shifting environment, it is also known as the Oxygen Catastrophe.
Those microbes that could adapt to the new oxygen-rich conditions were able to leave the ocean and underground niches and spread more freely across the Earth’s surface due to the oxygen flood. Soon after, the oxygen flood produced an ozone layer that protected against harmful solar ultraviolet radiation.
Additionally, rhodopsin evolved to absorb those wavelengths of sunlight since they are more abundant than in deep waters. The results can also be used in astrobiology. According to Schwieterman, the environment of early Earth was strange compared to that of the modern planet. We will learn vital skills for finding and identifying life abroad by studying how creatures here have changed over time and in various habitats.