More than 12,000 microfossils from northern Australian mudstone cores show the oldest known eukaryotes—dating roughly 1.7 to 1.4 billion years ago—lived only in oxygenated marine settings.
Chemical analysis of the surrounding rocks found fossils across habitats from coastal mudflats to open sea, but oxygen-free samples contained only simpler prokaryotic forms.
The oldest fossils in the collection reach about 1.75 billion years, making them the earliest known eukaryote fossils and extending evidence from a period when Earth’s oceans were often low in oxygen.
The Nature study strengthens the view that oxygen was a key driver in the rise of complex cells, a pivotal step that eventually enabled animals, plants and fungi.
If complex cells existed 1.75 billion years ago, what caused the billion-year delay before animal evolution?
Did the dawn of complex life on Earth hinge entirely on oxygen's arrival?
Ancient Eukaryote Fossils (1.7 Billion Years Old) Link Oxygen to the Rise of Complex Life and Guide Search for Extraterrestrial Life
Overview
A recent discovery of 1.7-billion-year-old eukaryote microfossils offers a crucial glimpse into the early evolution of complex life on Earth. These ancient microscopic organisms are important because they show the rise of mitochondria—a key step that transformed simple microbial mats into the diverse ecosystems we see today. The presence of mitochondria in these early eukaryotes marks a pivotal evolutionary leap, paving the way for all complex life forms, including plants, animals, and humans. This finding highlights how the development of complex internal cell structures was essential for the emergence and success of advanced life.