which fossil is the oldest?

Researchers at UCLA and the University of Wisconsin–Madison have confirmed that microscopic fossils discovered in a nearly 3.5 billion-year-old piece of rock in Western Australia are the oldest fossils ever found and indeed the earliest direct evidence of life on Earth.

The study, published Dec. 18, 2017 in the Proceedings of the National Academy of Sciences, was led by J. William Schopf, professor of paleobiology at UCLA, and John W. Valley, professor of geoscience at the University of Wisconsin–Madison. The research relied on new technology and scientific expertise developed by researchers in the UW–Madison WiscSIMS Laboratory.

The study describes 11 microbial specimens from five separate taxa, linking their morphologies to chemical signatures that are characteristic of life. Some represent now-extinct bacteria and microbes from a domain of life called Archaea, while others are similar to microbial species still found today. The findings also suggest how each may have survived on an oxygen-free planet.

The microfossils — so called because they are not evident to the naked eye —  were first described in the journal Science in 1993 by Schopf and his team, which identified them based largely on the fossils’ unique, cylindrical and filamentous shapes. Schopf, director of UCLA’s Center for the Study of Evolution and the Origin of Life, published further supporting evidence of their biological identities in 2002.

He collected the rock in which the fossils were found in 1982 from the Apex chert deposit of Western Australia, one of the few places on the planet where geological evidence of early Earth has been preserved, largely because it has not been subjected to geological processes that would have altered it, like burial and extreme heating due to plate-tectonic activity.

But Schopf’s earlier interpretations have been disputed. Critics argued they are just odd minerals that only look like biological specimens. However, Valley says, the new findings put these doubts to rest; the microfossils are indeed biological.

“I think it’s settled,” he says.

Using a secondary ion mass spectrometer (SIMS) at UW–Madison called IMS 1280 — one of just a handful of such instruments in the world — Valley and his team, including department geoscientists Kouki Kitajima and Michael Spicuzza, were able to separate the carbon composing each fossil into its constituent isotopes and measure their ratios.

Isotopes are different versions of the same chemical element that vary in their masses. Different organic substances — whether in rock, microbe or animal ­— contain characteristic ratios of their stable carbon isotopes.

Using SIMS, Valley’s team was able to tease apart the carbon-12 from the carbon-13 within each fossil and measure the ratio of the two compared to a known carbon isotope standard and a fossil-less section of the rock in which they were found.

“The differences in carbon isotope ratios correlate with their shapes,” Valley says. “If they’re not biological there is no reason for such a correlation. Their C-13-to-C-12 ratios are characteristic of biology and metabolic function.”

Based on this information, the researchers were also able to assign identities and likely physiological behaviors to the fossils locked inside the rock, Valley says. The results show that “these are a primitive, but diverse group of organisms,” says Schopf.

The team identified a complex group of microbes: phototrophic bacteria that would have relied on the sun to produce energy, Archaea that produced methane, and gammaproteobacteria that consumed methane, a gas believed to be an important constituent of Earth’s early atmosphere before oxygen was present.

It took Valley’s team nearly 10 years to develop the processes to accurately analyze the microfossils — fossils this old and rare have never been subjected to SIMS analysis before. The study builds on earlier achievements at WiscSIMS to modify the SIMS instrument, to develop protocols for sample preparation and analysis, and to calibrate necessary standards to match as closely as possible the  hydrocarbon content to the samples of interest.

In preparation for SIMS analysis, the team needed to painstakingly grind the original sample down as slowly as possible to expose the delicate fossils themselves — all suspended at different levels within the rock and encased in a hard layer of quartz — without actually destroying them. Spicuzza describes making countless trips up and down the stairs in the department as geoscience technician Brian Hess ground and polished each microfossil in the sample, one micrometer at a time.

Each microfossil is about 10 micrometers wide; eight of them could fit along the width of a human hair.

Valley and Schopf are part of the Wisconsin Astrobiology Research Consortium, funded by the NASA Astrobiology Institute, which exists to study and understand the origins, the future and the nature of life on Earth and throughout the universe.

Studies such as this one, Schopf says, indicate life could be common throughout the universe. But importantly, here on Earth, because several different types of microbes were shown to be already present by 3.5 billion years ago, it tells us that “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,” says Schopf.

Earlier studies by Valley and his team, dating to 2001, have shown that liquid water oceans existed on Earth as early as 4.3 billion years ago, more than 800 million years before the fossils of the present study would have been alive, and just 250 million years after the Earth formed.

“We have no direct evidence that life existed 4.3 billion years ago but there is no reason why it couldn’t have,” says Valley. “This is something we all would like to find out.”

UW–Madison has a legacy of pushing back the accepted dates of early life on Earth. In 1953, the late Stanley Tyler, a geologist at the university who passed away in 1963 at the age of 57, was the first person to discover microfossils in Precambrian rocks. This pushed the origins of life back more than a billion years, from 540 million to 1.8 billion years ago.

“People are really interested in when life on Earth first emerged,” Valley says. “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 … I think a lot more microfossil analyses will be made on samples of Earth and possibly from other planetary bodies.”

The research was supported by the NASA Astrobiology Institute at the University of Wisconsin–Madison and the Center for the Study of Evolution and the Origin of Life at UCLA. WiscSIMS is supported by the National Science Foundation (EAR-1355590) and UW–Madison.

The oldest known fossils, in fact, are cyanobacteria from Archaean rocks of western Australia, dated 3.5 billion years old.

Unfortunately, most early life forms are too small to be preserved in the fossil record. And too old — there are only really a few places on the planet with rocks ancient enough to carry that kind of fossil evidence.

As a result, some of the earliest traces of life we have detected on our planet are so faint that the fossil evidence that remains only reveals the movements of these microscopic organisms.

“It is a real detective story,” says William Schopf, a paleobiologist with the University of California, Los Angeles.

Life is believed to date back several billion years at least — and in that time, the geological cycle of our planet has changed a lot, even for rocks. Rocks and the fossils they carry are often buried in sediment. Over time, tectonic movement pushes these rocks back up to the surface, where tides, winds and other processes erode them away. As a result, most of the fossils that were once preserved of the earliest life would have disappeared due to erosion over time. The older the rock is, the greater the chance the fossil no longer exists, Schopf says.

Furthermore, geological cycles often pressure cook rocks, wiping out the fossils preserved inside in the process. There are only a few places on Earth where rocks older than 3.5 billion years can be found that still carry fossil evidence. Parts of western Australia, Greenland and South Africa have ancient rocks like these, exposed.

Schopf and his colleagues found worm-like patterns preserved in the Apex Chert — a rock formation in Australia dating back to about 3.465 billion years ago. They first discovered these supposed organisms in 1993, but the idea that these patterns represented ancient life was controversial. In 2018, Schopf published a follow-up study in Proceedings of the National Academy of Sciences that used secondary ion mass spectroscopy technology to reveal the ratio of carbon-12 and carbon-13 isotopes. This ratio revealed that the shapes preserved in the chert were characteristic of biological matter.

During this time, the planet did not yet have oxygen, Schopf says. Ancient iron doesn’t start to show traces of rust — a telltale sign of oxygen in the atmosphere — until about 3 billion years ago. It becomes more abundant about 2.8 billion years ago and common roughly 2.3 billion to 2.5 billion years ago.

“I don’t think oxygen-producing organisms developed until about 3 billion years ago,” Schopf says.

As a result, microorganisms older than 3 billion years may have used simplified photosynthesis that produced methane rather than oxygen.

Still, the microorganisms Schopf discovered in the chert in Western Australia may not be the oldest fossil evidence of life on the planet. That honor goes to stromatolites, which are sometimes mushroom-looking formations. Some of these may date back hundreds of millions of years earlier than the Apex Chert fossils Schopf discovered.

Stromatolites aren’t exactly fossilized remains of ancient life forms themselves. Researchers believe that cyanobacteria often erroneously called blue-green algae (it’s not actually algae), would have acted like the organisms do today, spreading across the surface of water to absorb sunlight.  Researchers believe the strange shapes of stromatolites were formed by cyanobacteria moving above the surface of sediment.

“It looks just like a rug, but it’s only 1-2 millimeters thick,” Schopf says.

Sediment would sometimes fall on top of these cyanobacteria mats, which would then push up above the sediment. As these processes repeated over and over again, it formed these strange hummocks or mushroom-like shapes that remain on the landscape today in places like Shark Bay in Australia.

Comprised of tiny tubes and filaments made of an iron oxide known as haematite, the microfossils are believed to be the remains of bacteria that once thrived underwater around hydrothermal vents, relying on chemical reactions involving iron for their energy.

If correct, these fossils offer the oldest direct evidence for life on the planet. And that, the study’s authors say, offers insights into the origins of life on Earth.

“If these rocks do indeed turn out to be 4.28 then we are talking about the origins of life developing very soon after the oceans formed 4.4bn years ago,” said Matthew Dodd, the first author of the research from University College, London.

With iron-oxidising bacteria present even today, the findings, if correct, also highlight the success of such organisms. “They have been around for 3.8bn years at least,” said the lead author Dominic Papineau, also from UCL.

The team says the new discovery supports the idea that life emerged and diversified rapidly on Earth, complementing research reported last year that claimed to find evidence of microbe-produced structures, known as stromatolites, in Greenland rocks, which formed 3.7bn years ago.

However, like the oldest microfossils previously reported – samples from western Australia dating to about 3.46bn years ago – the new discovery is set to be the subject of hot debate.

The discovery of the structures, the authors add, highlights intriguing avenues for research to discover whether life existed elsewhere in the solar system, including Jupiter’s moon, Europa, and Mars, which once boasted oceans. “If we look at similarly old rocks and we can’t find evidence of life, then this certainly may point to the fact that Earth may be a very special exception and life might just have arisen on Earth,” said Dodd.

Published in the journal Nature by an international team of researchers, the new study focuses on rocks of the Nuvvuagittuq supracrustal belt in Quebec, Canada.

The rocks are some of the oldest in the world and are believed to have formed around underwater hydrothermal vents – a theory backed up by various chemical signatures hinting at a submarine formation, as well as the presence of structures such as pillow basalts that are formed when lava encounters water.

“These rocks were of a period in time when we don’t know whether there was life,” said Dodd. “If we believe the long-standing hypothesis that life evolved from hydrothermal vents billions of years ago then these were the perfect rocks to look at for answering these questions.”

The authors say scrutiny of very thin sections of the iron-containing quartz in which the fossils were found, together with an analysis of the minerals within them and microfossils themselves, suggests the haematite structures were not formed by physical processes alone.

Instead, the authors write, “the tubes and filaments are best explained as remains of iron-metabolising filamentous bacteria, and therefore represent the oldest life forms recognised on Earth.”

Up to half a millimetre in length and half the width of a human hair, the filaments have a range of forms, from loose coils to branched structures with some apparently linked together through a central knob of haematite – structures, said Dodd, that are common to microbes known to have lived near deep sea vents.

“The microfossils’ structures in themselves are almost identical, very similar, to microfossils and micro-organisms we see in similar hydrothermal vent settings today,” said Dodd. Minerals linked to biological matter were also found with the tubes and filaments, the authors note.

Ancient human fossils discovered in Ethiopia could be as much as 2,30,000 years old, experts have revealed in a study. The fossils are known as Omo I.

The remains, first discovered in the late 1960s, are one of the earliest examples of Homo sapiens fossils. However, previous studies to date them placed them under 2,00,000 years old.

But a new study by the University of Cambridge suggests that the remains probably pre-dates a massive volcanic eruption in the area that happened 2,30,000 years ago.

The team of researchers dated the chemical fingerprints of volcanic ash layers that were found above and below the sediment where the fossils were first discovered.

But the study is far from over, said the experts. As of now, the new findings have pushed the minimum age for Homo sapiens in eastern Africa back by 30,000 years. However, new studies in the future can possibly extend the age further.

The discovery of the world's oldest Homo sapiens fossils was announced by archaeologists in 2017. It was a 3,00,000-year-old skull at Jebel Irhoud in Morocco.

For decades now, scientists have been trying to precisely date the oldest fossils in eastern Africa.

The Omo I remains were found in the Omo Kibish Formation in southwestern Ethiopia.

The region is an area of high volcanic activity. It is also a rich source of early human artefacts.

"Using these methods, the generally accepted age of the Omo fossils is under 200,000 years, but there's been a lot of uncertainty around this date," said Dr Céline Vidal from Cambridge's Department of Geography, the paper's lead author.

"The fossils were found in a sequence, below a thick layer of volcanic ash that nobody had managed to date because the ash is too fine-grained," he added.

Last year, researchers in China discovered an ancient skull that belonged to a completely new species of human.

The specimen, which was actually found at Harbin in 1933, was nicknamed 'Dragon Man' and it came to the attention of scientists only in 2021.

It was reportedly kept hidden in a well for 85 years to protect it from the Japanese Army.

The oldest fossils are over 3.5 billion years old, which may mean that life emerged relatively early in the Earth’s history (Earth is 4.543 billion years old).

photo source: Wikimedia Commons

A tiny fossil containing the remains of the world’s oldest insect was initially found in 1920s, but not studied until recently. The fossil contains the jaw remains of Rhyniognatha hirsti and is about 400 million years old. Scientists say that the findings push back the origins of winged insects by 80 million years.

Rhyniognatha is not only the oldest-known insect, it was most likely one of the first animals to arrive on land.

Although Rhyniognatha‘s mandible structure is only ever found in winged insects, scientists cannot say with absolute certainty whether or not it had wings as no wing remains have been found. Scientists suggest that Rhyniognatha provides clues into why insects started to develop wings — shortly before Rhyniognatha lived, plants became massive and tall. Early insects fed on these plants and needed to develop a way to reach the plant tops.

photo source: sci-news.com

Fossils of the earliest-known fungus, Tortotubus, were discovered by paleontologists in Scotland in 2016. Paleontologists estimate that the fossil is about 440 million years old. Not only is the Tortotubus fossil the oldest fungus, it is the oldest fossil of any strictly land-based organism ever found.

Tortotubus has cord-like structures that are similar to modern fungi. These structures are also seen in other land-based organisms and scientists believe that they helped Tortotubus spread out and colonize land surfaces. Tortotubus and other early fungi played an important role in forming the soil and nutrients that were needed for plants and animals to transition onto land.

photo source: Slate

The Metaspriggina fossil found in the Burgess Shale is one of the oldest and best-preserved fossils of a primitive fish. In 2014, scientists released a study on Metaspriggina and announced that it played a key role in the development of jaws. Unlike other early fish, Metaspriggina had seven pairs of gill arches rather than the individual gill arches of the other fish.

Scientists believe that the pair of gill arches closest to Metaspriggina’s head evolved into the upper and lower jaw bones. For several decades, paleontologists believed that a creature like this existed, but the discovery of Metaspriggina provides the first fossil evidence of early jaw development.

photo source: Slate

The oldest trilobite (ancient marine arthropods) fossils are about 525 million – 500 million years old. They are known as Redlichiida and they first appear in the fossil record in the Lower Cambrian period. The earliest Redlichiida are considered the ancestors of all other trilobite species.

Redlichiidas were flat and had an oval-shaped exoskeleton. Very few fossil specimens have any appendages, but scientists do know that Redlichiidas follow typical trilobite patterns in terms of the number, placement, and types of legs, antennae, and gills. Most Redlichiida fossils have been found in the Emu Bay shales of Southern Australia and the Maotianshan shales near Chengjiang in China.

photo source: Wikimedia Commons

Pikaia fossils were first discovered by Charles Walcott in 1911. He found them in a mountain called Pika Peak (for which they are named) in Alberta, Canada. The fossils are about 523 million years old and Pikaia are the oldest known ancestor of modern vertebrates. However, there is some debate over whether or not Pikaia actually was a vertebrate ancestor even though it does have early vertebrate characteristics.

Recreations of what Pikaia looked like suggest it was similar to modern-day lancelets and swam like an eel. It also had a pair of large antennas on its head and short appendages on both sides of it head. There are 114 known fossils of Pikaia, which has allowed scientists to paint an accurate picture of what Pikaia may have looked like.

photo source: The Washington Post

Researchers from China uncovered “seaweed-like” fossils in 2016. The find was a surprise because the organisms trapped in the fossils were visible to the naked eye, which is unusual for such ancient multi-cellular lifeforms known as eukaryotes. About 167 fossils were found and dated to about 1.56 billion years ago.

Before the new discovery, the earliest known examples of multi-cellular life of this size weren’t seen in the fossil record until about 600 million years ago.

The time period before this in the fossil record is known as the “boring billions” because researchers had previously only found microfossils from this far back. Additionally, the shape of the fossils suggest that these organisms may have been photosynthetic.

photo source: Wikimedia Commons

Although a claim in 2017 says that the oldest fossils come from rocks found in Canada, the stromatolites from Archaean rocks in Western Australia are widely accepted as the oldest-known fossils with strong evidence. Stromatolite fossils are distinctive and look like layered rock formation. They were formed by ancient blue-green algae known as cyanobacteria and the oldest stromatolites are estimated to be about 3.5 billion years old.

Most of the stromatolites found so far are old and dead, but in 1956 living stromatolites — which are extremely rare — were found in Hamelin Pool in Western Australia. Hamelin Pool has the most abundant and diverse living stromatolites found anywhere in the world. The water in the area is twice the salinity of regular seawater, which allows cyanobacteria to thrive.

photo source: The New York Times

In early 2017, scientists found tubelike microscopic bacteria on hematite ore that are currently believed to be the oldest fossils in the world. The fossils are similar to those found at hydrothermal vents, where thriving biological communities exist. Though other scientists are skeptical about their claims, the scientists who found the fossils say they are at least 3.7 billion years old and may even be older than 4 billion years.

These scientists are hopeful that the new fossils will shed some insights into early life on Earth. If the fossils really are 4.2 billion years old this will provide evidence that life began quickly after the Earth’s oceans were formed.