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What Are the Oldest Fossils Ever Found?

Fossils are the hardened remains or imprints of long dead organisms that provide a window into the ecological past. They can form many different ways, but they all provide a unique look at an organism that lived long ago. Fossils are often millions of years old, but the world's oldest fossils are even much more ancient.

Stromatolites
- Stromatolites are the oldest fossils in the entire fossil record. They formed by trapping microorganisms like algae in sedimentary layers, which then cemented over time, giving paleontologist layers of tiny organisms to study. They often form in shallow water where sand grains are constantly washed over rocks.
Age
- The oldest confirmed stromatolite containing microorganisms in the geologic record is approximately 2.724 billion years old, which is roughly half the age of the Earth. This indicates that microbial organisms like algae had already formed during this period.
Abundance
- Stromatolite-building microorganisms were most common during the Precambrian era. However, their numbers declined sharply during the Cambrian. This is most commonly associated with the development of algae-grazing animals that would eat at the rocks they developed on before they had a chance to fossilize. They are very rare in modernity, though they can occasionally be found in marine lagoons, particularly in the Bahamas.
Animal Fossils
- The oldest animal fossils currently on record belong to sponges found in Australia. The sponges are believed to be between 650 million and 640 million years old, which would predate the next oldest discovered fossils by 90 million years.

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