Confirmed in 2017 to be the oldest known fossils on Earth, these prehistoric bacteria from Western Australia are 3.5 billion years old. But some believe that there are even older fossils waiting to be discovered.
UW-MadisonA photo of the prehistoric rock samples analyzed by researchers at UW-Madison.
The Earth is full of clues about its past. Fossils are one way that the planet provides a glimpse at the many creatures and ecosystems that came before us. But how far back do these records actually go?
According to a study published by the University of Wisconsin–Madison in conjunction with UCLA, a rock from Western Australia answers this question.
After examining the fossils in the rock, researchers have determined that they are the oldest fossils ever found, dating back about 3.5 billion years. Amazingly, the prehistoric rock in question contains 11 microbial specimens, some of which represent long-extinct bacteria and others that are remarkably similar to microbes that still exist on Earth today.
Microfossils Aren’t A New Discovery
J. William Schopf/UCLAOne of the microfossils found in the 3.5-billion-year-old rock from Western Australia.
The fossils found in the prehistoric rock are known as microfossils, because they are so small that they can’t be seen by the naked eye. In fact, each one of them measures just 10 micrometers wide. For scale, this means that eight of these tiny fossils could fit along the width of a single human hair.
Microfossils were first noted in 1993, by J. William Schopf, the lead author of the more recent study and a paleobiology professor working at UCLA. Schopf first described the tiny fossils in a science journal, after he was drawn to their remarkable cylindrical and filamentous shapes.
In 2002, he published another paper on microfossils, providing more evidence that they were indeed biological entities, and not just mineral or geologic anomalies. However, much of Schopf’s early work was criticized and even disputed. Some critics believed that the microfossils he observed were merely unusual minerals that only resembled biological specimens.
J. William Schopf/UCLAThe lead author of the study, J. William Schopf.
Schopf first found the rock that ended up containing the oldest known microfossils in 1982 from the Apex chert deposit in Western Australia. The fossils were preserved in the rock formation due to the region’s unique geological conditions, which lack the processes that would’ve altered the specimens, such as extreme heat from plate-tectonic activity.
Today, any dispute over the legitimacy of these prehistoric microbes has been settled, declared John W. Valley, a researcher from the University of Wisconsin–Madison who worked on the project with Schopf.
How The Oldest Known Fossils Were Identified Through New Methods
Jeff Miller/UW-MadisonJohn Valley and another researcher, Kouki Kitajima, working in the Wisconsin Secondary Ion Mass Spectrometer Lab (WiscSIMS) to analyze the prehistoric fossils.
Schopf and Valley were able to identify these microorganisms using a secondary ion mass spectrometer (SIMS) at UW–Madison.
Fossils this old hadn’t been analyzed using SIMS before. So it took Valley and his team almost 10 years to develop a process to accurately analyze and identify the samples, building off years of earlier research.
Using SIMS, researchers were able to separate the carbon in each fossil into isotopes and measure the ratios. Carefully examining the ratios then helped to determine that the fossils had indeed once been living things.
Wikimedia CommonsA stromatolite rock sample, similar to the one analyzed from Western Australia.
The research team was also able to assign identities to the fossils based on the carbon isotope ratios, which showed that they were “a primitive, but diverse group of organisms,” Schopf explained. That group of organisms was, more specifically, prehistoric bacteria and microbes. Incredibly, the results showed 11 different microbial specimens.
Some of the specimens were from a domain known as Archaea, a group of bacteria that produced methane gas. Other specimens were forms of gammaproteobacteria, a group that consumed methane gas. Yet others were phototrophic bacteria, which primarily relied on the sun to produce energy.
What The Oldest Fossils Ever Found Tell Us About Our Planet And Beyond
Jeff Miller/UW-MadisonA sample of the 3.5-billion-year-old rock from the Apex chert deposit, which contained the oldest fossils ever found.
The biology of these prehistoric bacteria helps paint a better picture of what life on Earth was really like billions of years ago.
The identification of these methane-producing and methane-consuming organisms provides a window into understanding how some prehistoric life forms may have survived in an atmosphere that lacked oxygen.
The phototrophic bacteria, which mainly required the sun for energy, also lend themselves to research on how prehistoric organisms could have survived in an environment entirely different from the one we know today.
Schopf believes that research like this can tell us a lot about our planet — and perhaps the entire universe. Considering the difficult conditions that these bacteria had to endure, it’s possible this model of life-form could exist elsewhere in the universe. Schopf says that life could potentially even be common throughout the galaxies.
But the most important implications of this discovery indicate something larger for Earth, Schopf clarified. If diverse bacteria already existed 3.5 billion years ago, who knows when the earliest life on Earth actually began.
John Valley/UW-MadisonApex Chert in Western Australia, the site where the rock containing the oldest known fossils ever was found.
“Life had to have begun substantially earlier — nobody knows how much earlier — and confirms it is not difficult for primitive life to form and to evolve into more advanced microorganisms,” Schopf explained.
In previous research, Valley found that liquid oceans were present on Earth about 4.3 billion years ago, only 250 million years after the planet formed.
“People are really interested in when life on Earth first emerged,” Valley remarked. “This study was 10 times more time-consuming and more difficult than I first imagined, but it came to fruition because of many dedicated people who have been excited about this since day one.” He added, “I think a lot more microfossil analyses will be made on samples of Earth and possibly from other planetary bodies.”
There Could Still Be Older Fossils Out There That Haven’t Been Found Yet
Matthew Dodd/PAA study from the University College London suspects that the oldest fossils in the world come from Quebec, Canada.
The question of what fossil is really the oldest specimen is still debated amongst researchers today. While it is generally accepted that the 3.5-billion-year-old fossils from Western Australia are the oldest known specimens, an earlier study from the University College London suggests that the oldest fossils may actually be 4.3 billion years old, inside rocks located in the Nuvvuagittuq Supracrustal Belt in Quebec, Canada.
“Our discovery supports the idea that life emerged from hot, seafloor vents shortly after planet Earth formed. This speedy appearance of life on Earth fits with other evidence of recently discovered 3,700 million year old sedimentary mounds that were shaped by microorganisms,” researcher Matthew Dodd explained.
However, after Valley’s more recent research, Valley said, “We have no direct evidence that life existed 4.3 billion years ago but there is no reason why it couldn’t have. This is something we all would like to find out.”
Jeff Miller/UW-MadisonResearcher John Valley in his office at UW–Madison.
Even before Schopf and Valley’s discovery, Australia was home to many of the oldest fossils ever found on Earth. In 2011, researchers at the University of Western Australia found fossils that were 3.4 billion years old. Just like Valley and Schopf, the researchers used isotopes to analyze the fossils.
Researchers are still on the lookout for fossils older than 3.5 billion years old, but as of now, the rock from Western Australia takes the cake.
After reading about the oldest known fossils ever found, see how a PhD student discovered a new prehistoric reptile species by reuniting two fossil halves. Then, take a look at the oldest ant fossil ever found.
