Imagine Earth at a time when it was almost unrecognizable—a landscape that was barren and with barely breathable air. That is what Earth looked like about 1.75 billion years ago. But scientists now have some very exciting new evidence about how life on Earth first began to take off during those ancient times. It has allowed researchers to push the date of photosynthesis far back in time with the enabling of fossils from northern Australia of tiny creatures, which gives crucial digital insights into the emergence of life on Earth.
Scientists have reported the discovery of microfossils bearing what they believed was the oldest known signature of photosynthesis—dating back 1.75 billion years—at least. These ancient remnants come from cyanobacteria, small organisms that could have existed on Earth as far back as 3.5 billion years ago. Previously, the oldest confirmed cyanobacteria fossils dated to around 2 billion years ago, so this new finding brings it back a whopping 1.2 billion years.
What is it that makes this so vastly different? Well, Cyanobacteria are credited with being the major kick-starter of the Great Oxidation Event, a periodic time approximately about 2.4 billion years ago when there was an extreme rise in oxygen levels on Earth’s atmosphere. It is this spike in Oxygen which became critical for life as we know it to this day, because without it, the evolution of complex organisms would have simply been impossible.
It is through the discovery of small structures found in these ancient fossils, called thylakoids, that photosynthesis could happen: using light, water, and carbon dioxide to drive energy and releasing oxygen thereafter. Such are structures containing chlorophyll, which is a pigment that aids in the capture of sunlight. The finding of the chlorophyll in the fossils was much like striking gold because it clearly told them that photosynthesis had already evolved.
“This discovery implicates the unambiguous identification of early oxygenic photosynthesizers and a new redox proxy to probe early Earth ecosystems,” they wrote. It virtually impinges on the inference that these ancient photosynthesizers were at work, pumping oxygen into the environment and giving rise to conditions under which life could exist.
Imagine you were detectives trying to piece together clues at a crime scene. Any new evidence that turns up helps piece together what might have happened. These ancient fossils, in many ways, are something like that—clues that put the scientists in a position to make out early Earth. Their discovery of photosynthesis so far back pushes the date for cyanobacteria pumping oxygen into the atmosphere much earlier than had been previously thought, setting the stage for the big bang of life forms that came later.
But that’s not all. This is the proverbial “tip of the iceberg”. A whole research team is going to study the cells from fossils around the world to try and see if they fit this new timeline. “We predict that similar ultrastructural analyses of well-preserved microfossils might expand the geological record of oxygenic photosynthesizers and of early, weakly oxygenated ecosystems in which complex cells developed,” the authors noted.
Now, consider this: every small fossil, moment of this time capsule, is that time in which life on Earth had just barely begun to take shape. It’s overwhelming to think what such small, single-celled organisms could do: what ultimately helped take part in shaping our very planet today—into one importantly that includes you and me living upon it.
So next time you come across a morass of green algae or some cyanobacterium down the microscope, remember you’re gazing at some of Earth’s oldest living things. Humble organisms like these were among the first to do photosynthesis, setting the scene for an oxygen-rich world in which we live today. And who knows what other ancient secrets lie waiting to be uncovered in rocks below our feet? It is barely a century since scientific discovery really began. Yet with every new find, we creep closer to the understanding of the fantastic story of life on Earth.
