Scientists have long wondered what Earth was like in its most nascent stage. More importantly, researchers have tried to understand how life began to emerge from a nearly inhospitable planet billions of years ago.
A research team at the University of California—Riverside have attempted to reconstruct how certain organisms lived (and indeed, thrived) in the earliest eons of planet Earth. Specifically, the research team explored how certain organisms lived on a planet where oxygen wasn’t a readily available resource to sustain life. Our understanding of how life emerged in an oxygen-deficient environment could help researchers identify signs of life beyond our planet.
The team’s work is described in a recent paper published in Molecular Biology and Evolution.
The research team looked specifically at proteins that capture and synthesize light: rhodopsins. These proteins can take light energy, which was abundant in an early Earth that lacked ozone protection, and turn it into energy. This is all happening absent existing photosynthetic properties we see in plants today.
Rhodopsins are common in many modern organisms. For example, they are found in human eyes to help us see light. To understand how these key proteins might have been used in organisms living eons ago, researchers used machine learning to study the rhodopsin proteins, with a particular eye towards how these proteins evolved over billions of years.
Rhodopsins we can observe nowadays can absorb a range of colors. According to machine learning analysis, however, these rhodopsins were calibrated towards absorbing green and blue light, specifically.
So what does that mean?
Researchers speculate that this evolutionary adaptation has to do with a lack of ozone layer billions of years ago. Organisms lived deep underwater in the primarily-oceanic age of our planet to avoid exposure to the sun’s harmful rays. Blue and green light happen to be more suited to breaking through deep sections of ocean. As the planet became more oxygen rich, rhodopsins evolved to be able to capture a wider range of light colors, which we see today.