Tiny 1.7-Billion-Year-Old Fossils Could Reveal How Complex Life Began

Tiny 1.7-Billion-Year-Old Fossils Could Reveal How Complex Life Began — on Earth and Beyond

Paleontologists are scouring some of Earth's oldest rocks for microscopic fossils that could reveal how simple microbes made the leap to complex life — eukaryotes, the lineage behind every plant, animal and fungus. The hunt, centered on ancient coastal basins in Svalbard and Australia, may also help estimate whether complex life can emerge on other worlds.

Key Takeaways

Paleontologists are scouring some of Earth's oldest rocks for microscopic fossils that could reveal how simple microbes made the leap to complex life — eukaryotes, the lineage behind every plant, animal and fungus.
The hunt, centered on ancient coastal basins in Svalbard and Australia, may also help estimate whether complex life can emerge on other worlds.

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The search for life on Mars or on icy moons such as Europa and Enceladus may capture more attention, but another astrobiology mystery is much closer to home: scientists are still trying to understand when the first eukaryotes appeared on Earth and how those organisms set the stage for complex life. The question matters because microbial organisms dominated Earth for roughly 90 percent of the planet's history — and reconstructing the transition from a microbe world to one filled with plants, animals and fungi could help scientists understand whether complex life might develop elsewhere in the universe.

The broad timeline is known. Life originated on Earth more than 3.5 billion years ago; cyanobacteria and oxygen-producing photosynthesis were present by at least 2.3 billion years ago; eukaryotes — cells with a nucleus enclosing their DNA and organelles such as mitochondria — had appeared by at least 1.7 billion years ago. Algae followed at least one billion years ago, and animals appeared at least 570 million years ago. To reach the common ancestor shared by the plant and animal kingdoms, researchers must look back around 1.6 billion years.

Finding the earliest eukaryotes, however, is extraordinarily difficult. Organisms older than 500 million years lacked shells and skeletons, so paleontologists depend on rare environments that preserved fragile cells and soft tissues. Ross Anderson, a paleontologist at the University of Oxford, studies the chemistry of ancient rocks to identify the environments most likely to have preserved them — including a roughly 100-square-kilometer region near Svalbard, Norway, once covered by a shallow sea, and ancient coastal basins in Australia, where researchers last year discovered some of the oldest known eukaryotic microfossils, dating to roughly 1.75 billion years ago. Clay deposits, he notes, are especially promising for preserving ancient remains.

The hunt has implications far beyond Earth's biological past. Anderson says much of his work on clay deposits was originally motivated by the search for life on other planets: by learning which environments preserve ancient organisms here, scientists become better equipped to recognize possible signs of life elsewhere. Understanding how life emerged and became increasingly complex on our own planet is therefore an important part of estimating how likely life is to arise and evolve beyond it.