Discover Why the Oldest Animal Fossil Is Almost 1 Billion Years Old

Stromatolite from the Paleoarchean of Western Australia.
© James St. John / Flickr

Written by Kyle Glatz

Published: February 3, 2023

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Modern humans have existed for just about 200,000 years old. That’s a brief moment in time compared to the age of all life on the planet. How long has life been occurring on the planet? Well, that’s a difficult question to answer. Yet, the oldest animal fossil ever discovered has given scientists some insight into how long animals have lived on Earth in some form.

Take a look at an ancient animal fossil that could provide evidence of animal life on the planet from almost a billion years ago!

When Was Earth First Capable of Sustaining Life?

Scientists estimate that Earth is about 4.5 billion years old. They used radiometric dating on all sorts of rocks on the planet and on those from other celestial bodies like the moon and meteorites to determine the age of the planet.

Yet, life did not exist on the planet 4.5 billion years ago. The first major reason that the planet wasn’t ready for life at that time was its temperature. Simply put, the planet was too hot at its formation for life to exist. In fact, it was probably inhospitable to life for the first several hundred million years.

Recent studies have shown that conditions capable of sustaining life on Earth may have existed as early as 4.1 billion years ago. This estimate is based on scientists finding evidence of the building blocks of life that would have allowed organic compounds to form while Earth was in its infancy.

Specifically, scientists found a 4.1-billion-year-old zircon containing graphite. Researchers insist that this substance is potentially biogenic, possibly providing proof that life had flourished much earlier than originally suggested.

Yet, finding the building blocks of life and finding evidence of life are not always the same. Moving forward, let’s consider some of the fossil evidence scientists have discovered about life on Earth.

planet earth

Recent studies have shown that conditions capable of sustaining life on Earth may have existed as early as 4.1 billion years ago.

© Saengngoen

What Are the Oldest Fossils on Earth?

Scientists have many different estimates about when life began on Earth. As previously mentioned, some believe that life could have started on Earth about 4.1 billion years ago. That’s only 400 million years or so after Earth formed. The oldest animal fossils would not appear for billions of years after life began.

However, fossils demonstrate that life on Earth probably began at some point about 3.8 to 3.5 billion years ago. The fossils dating back to almost 3.8 billion years ago were found in the Nuvvuagittuq Greenstone Belt in Canada. Researchers found putative fossilized microorganisms that lived about 4.2 to 3.77 billion years ago.

The fossils dating back to 3.7 billion years ago are still under investigation. Yet, they’re worth examining. According to researchers, the fossils were stromatolites, the structures created by microorganisms in sediment.

Scientists found the fossils in Greenland, and they predated the next-oldest fossils by upwards of 200 million years! Some researchers are not convinced that the fossils captured actual life. Instead, they may have merely captured the movement of carbonite-rich fluids.

If the stromatolites from Greenland turn out to not be the oldest fossils, then the fossils dating back to 3.5 billion years ago would be the oldest. Fossils of cyanobacteria are the oldest confirmed fossils ever discovered. The fossils of this bacteria were found in rocks in western Australia.

The fossil specimens for the cyanobacteria were also stromatolites, representing layer upon layer of cyanobacteria mounds. Scientists use many different methods to examine these fossils and learn all they can about the conditions of early life on Earth.

All in all, life has existed for a very long time on Earth, but none of those fossils were from animals.

Stromatolite, Western Australia

Stromatolites discovered in Western Australia are the oldest confirmed fossils ever discovered.

©James St. John / Flickr – Original / License

What’s an Animal?

Before we consider the oldest animal fossils, we need to define what they are. Basically, animals are multicellular eukaryotic organisms that belong to the phylogenetic kingdom Animalia. That definition may not simplify matters that much.

However, that definition does ensure that single-celled organisms, bacteria, and other living creatures are not considered animals. That helps when considering the oldest animal fossils that have ever been discovered.

Having outlined the boundaries of this inquiry, it’s time to consider the oldest animal fossils.

How Old is the Oldest Animal Fossil?

The oldest animal fossil ever discovered is 890 million years old. The fossils of this animal belong to relatives of the sea sponge. The sponges had a mesh-like structure that was preserved in northwestern Canada.

The study’s author, sedimentary geologist Elizabeth C. Turner of Laurentian University, believes that the fossilized structures in the 890-million-year-old microbial reefs could be evidence of the oldest form of animal life ever recorded.

If confirmed, the discovery would be about 300 million years older than the next-oldest animal fossils. Those belonged to a creature called Dickinsonia that lived about 558 million years ago.

Still, not everyone is convinced that what Elizabeth Turner found was actually animal fossils. The structures imprinted on the rocks are not enough to sway skeptics, but it’s still going down as the oldest animal fossil for these purposes.

What is the Oldest Mammal on Earth?

Knowing the oldest animal fossils ever found, it’s interesting to consider the amount of time that passed before mammalians walked the earth.

Brasilodon quadrangularis, a shrew-like animal, is considered the oldest mammal ever discovered, and it lived some 225 million years ago. That means this small creature was running around at the same time as many dinosaurs.

Scientists had once considered Morganucodon to be the earliest mammal. Teeth from this animal date back to about 205 million years ago. Haramiyids are another contender for the oldest mammals on Earth. Records of this creature date back to about 208 million years ago, but scientists are uncertain of whether or not it was a mammal.

Scientists lack a great deal of information since only hard tissues from that era were preserved in the fossil record.  

Brasilodon quadrangularis is the oldest mammal discovered
Brasilodon quadrangularis

(on left)

is a shrew-like animal considered the oldest mammal ever discovered, living some 225 million years ago.

©Made by Jorge Blanco., CC BY 2.5 <>, via Wikimedia Commons – Original / License

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About the Author

Kyle Glatz is a writer at A-Z-Animals where his primary focus is on geography and mammals. Kyle has been writing for researching and writing about animals and numerous other topics for 10 years, and he holds a Bachelor's Degree in English and Education from Rowan University. A resident of New Jersey, Kyle enjoys reading, writing, and playing video games.

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