Decoding the past: Earth’s most ancient fossils and what they tell us

The history of life on Earth extends far beyond the dinosaurs and ancient mammals that usually come to mind when we think of fossils. Believe it or not, scientists have actually found signs of life from billions of years ago.

But which are the oldest? Let’s take a look.

The following list is not exhaustive, and some fossils that are older than some or all of the list entries may have been discovered since the time of writing. However, the list of the oldest fossils currently known to science is in numerical order.

1. Microfossils from the Nuvvuagittuq Greenstone Belt (3.7 to 4.28 billion years old)

First up on our list of oldest fossils ever found are the microfossils of the Nuvvuagittuq Greenstone Belt . The rock sequence is located on the eastern shore of Hudson Bay, roughly 25 miles (40 km) southeast of Inukjuak , Quebec.

This belt consists of a sequence of metamorphosed mafic to ultramafic volcanic rocks and associated sedimentary rocks. These rocks have undergone extensive metamorphism and are some of the oldest surface rocks on Earth.

However, most interestingly, in 2017, it was reported that the rocks may contain what is yet to be confirmed as the oldest traces of life on Earth. In this case, the fossils consist of a series of what appear to be microscopic filaments that early microorganisms could have created.

However, it should be noted that this is hotly contested, with some experts arguing they may be abiotic.

2. Graphite in Greenland’s Isua supracrustal Belt (3.7 to 3.8 billion years old)

Next up on our list is not a fossil per se , but one of the oldest indirect signs of what may indicate biological activity. Some graphite deposits in Greenland’s Isua supracrustal Belt contain isotopic signatures indicating ancient biological activity.

These rocks, laid down during the Archaean Eon, are metamorphosed mafic volcanic and sedimentary rocks. Because of its age, this formation has been the focus of many investigations into the search for early life on Earth.

Some may have found it. The graphite’s isotopic composition suggests that ancient microorganisms produced it, likely some of the earliest life forms on the planet.

For example, in 1996, geologist Steve Mojzsis and his colleagues proposed that the isotopically light carbon found in the structure’s carbon-rich layers suggested biological activity had occurred there. Other studies have also claimed to have found evidence of stromatolites, but this is hotly debated.

3. Greenland stromatolites (3.7 billion years old)

Next on our list are the famous stromatolites of Greenland , also located in the Isua supracrustal Belt. These potentially fossil-containing rocks are believed to have formed around 3.7 billion years ago.

If true, this would make them the first concrete evidence of very early life on Earth. Claims about the biological origin of structures that resemble stromatolites have been disputed, but both sides of the argument are actively researching this area.

If you are unaware, stromatolites are layered structures formed by cyanobacteria, which are simple photosynthetic organisms. These structures have played a crucial role in shaping Earth’s atmosphere throughout time by producing oxygen.

You’ll see a few other examples in the list below. And our next entry is a prime example.

4. Warrawoona Group stromatolites (3.46 billion years old)

Next on our list of oldest fossils is the famous Warrawoona Group stromatolites . Believed to have formed around 3.46 billion years ago, these remnants of long-dead microorganisms are in today’s Pilbara region of Western Australia.

While not the oldest, the Nuvvuagittuq Greenstone Belt is indeed biological; they are the oldest confirmed fossils ever found.

The fossils of this rock sequence are commonly found in ancient Archean chert, a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz.

5. Western Australia’s Pilbara Craton Sulfide deposits (3.48 billion years old)

Next up on our list of the world’s oldest fossils is the Pilbara Craton Sulfide deposits in Western Australia. Dated to around 3.48 billion years ago, the presumed microfossils within them could be some of the oldest yet discovered.

Given the nature of the sulfide deposits, the hypothesized little critters found within are believed to have been sulfur-metabolizing bacteria. These microorganisms would have thrived in an environment where sulfur compounds were abundant.

Modern-day hydrothermal vents would be a good proxy for the kind of environment. The fossils, or, more technically speaking, pseudofossils , consist of microstructures that mimic true microfossil structures found elsewhere. While hotly debated, these may be the earliest sulfide-eating bacteria ever discovered.

6. Microbial mats from the Barberton Greenstone Belt (3.47 billion years old)

The microbial mats from the Barberton Greenstone Belt in South Africa are sixth on our list. Believed to have formed around 3.47 billion years ago, these rocks contain what are believed to have been some of the earliest shallow-water microbial mats ever found.

For the uninitiated, microbial mats are layers of microorganisms that stick together, often forming complex and resilient ecosystems. They are still common structures today.

The fossils within consist of a series of cell-sized, presumed prokaryotic fossils. The paleontological community widely accepts these fossils as the earliest bona fide fossils from the Archaean Eon.

7. Microfossils in Australian Apex Chert (3.465 billion years old)

Last but by no means least on our list of the world’s oldest fossils are the microfossils of the Australian Apex Chert formation . Thought to have formed around 3.465 billion years ago, the presumed preserved bacteria within are some of the earliest ever discovered.

The chert is believed to have formed from the remains of the sediment from an ancient lake or ocean. The preserved fossil remains once lived on the surface of the sediment and were later trapped and preserved to the present day.

These bacteria fossils are only 10–20 micrometers long and can only be seen through a microscope.

And that’s your lot for today.

As far as we know, the above are the oldest evidence of life on our planet yet dug up from the mists of time. As time passes, most, if not all, will likely be removed from the list.

But, as the saying goes, only time will tell.