1.7-billion-year-old fossils reveal oldest known eukaryote evidence

September 27, 2026 at 05:23 PM2 min

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Fossils from drill cores in northern Australia, dating to 1.75 billion years ago, are the oldest known eukaryote fossils globally, according to a study published in Nature. The discovery provides key evidence about the evolutionary leap that led to all complex life on Earth. The findings come as researchers debate whether oxygen was scarce when eukaryotes first evolved.

Key Facts

The oldest fossils from the Northern Territory drill cores date back to 1.75 billion years ago.
The study was published in the journal Nature.
The last common ancestor of all living eukaryotes resulted from the symbiotic union of at least two prokaryotic microbes: an archaeon and a bacterium.
Nearly all eukaryotes alive today use oxygen for their survival through aerobic respiration.
Geological evidence suggests oxygen was likely much scarcer when eukaryotes were first evolving.

The Discovery

Dozens of trays containing cylindrical rock cores are stored in an open-air warehouse in Darwin, Australia, at the Northern Territory Geological Survey. The cores were drilled hundreds of metres below the surface by mineral exploration companies decades ago. Some of these cores are mudstone, a sedimentary rock formed from hardened seafloor mud. Within these mudstones are fossils of microscopic organisms buried on the seafloor of an ancient inland sea that covered much of northern Australia over 1.5 billion years ago. The fossils show a level of cellular complexity not seen among prokaryotes but common in eukaryotes.

Eukaryote Origins

All life on Earth can be placed into one of two fundamentally different cellular types: prokaryotes and eukaryotes. Prokaryotes, including bacteria and archaea, have simple cellular organization and are mostly single-celled. Eukaryotes, including all animals, plants, algae, and fungi, have more complicated cells featuring a nucleus and specialized structures such as organelles. Based on observations from the genes of living organisms, it is now widely agreed that the last common ancestor of all living eukaryotes resulted from the symbiotic union of at least two prokaryotic microbes: an archaeon and a bacterium. The eukaryotic revolution transformed the planet, leading to the rise of animals and eventually to humans.

Oxygen Debate

Many types of bacteria can live and grow in places without oxygen, but nearly all eukaryotes alive today use oxygen for their survival. Aerobic respiration, breaking down food using oxygen, provides the vast amounts of energy that complex life demands. The idea that oxygen has always been beneficial for all eukaryotes has come under fire in recent years following discoveries of enigmatic eukaryotes that can thrive in conditions without oxygen. There is mounting evidence from the geological record that when eukaryotes were first evolving, oxygen was likely much scarcer. This means oxygen-free marine habitats would have been the norm during early eukaryotic evolution.