On the hunt for Earth’s first complex life
Bear Island in the Barents Sea which is a paleontological hotbed known for preserving ancient microfossils. Credit: Wikipedia How life started on our own planet may not seem as interest...
How life started on our own planet may not seem as interesting as finding evidence of life on Mars or the icy moons Europa or Enceladus. But the search for the first eukaryotes on Earth remains as important to astrobiology as finding life on a far-flung planet. That's in part because, for 90% of Earth's history, life was microbial.
"On Earth, life originated more than 3.5 billion years ago," Ross Anderson, a paleontologist at the UK's University of Oxford, said. "We had cyanobacteria and oxygenic photosynthesis at least 2.3 billion years ago; then we had eukaryotes at least 1.7 billion years ago."
They were followed by algae at least 1 billion years ago, probably even earlier. Then the animal kingdom arrived at least 570 million years ago, probably slightly earlier.
But to find the common ancestor of the plant and animal kingdoms, you must go back to something like 1.6 billion years ago, Anderson said.
And so-called crown eukaryotes—the earliest eukaryotes on Earth—are thought to have been fundamental to the development of complex life here. In fact, Anderson unequivocally considers eukaryotes to be Earth's first complex life.
What are eukaryotes?
Eukaryotes have a cell nucleus in which DNA is enclosed, but they also have organelles, subcellular structures in their cells, such as mitochondria, that allow energy-intensive lifestyles.
"It's the eukaryotes that have developed complex multicellularity and macroscopic forms; all the animals, plants and fungi that we see around the world are eukaryotic," Anderson said.
No organisms older than 500 million years had shells or skeletons because they hadn't evolved yet. As a result, paleontologists are reliant on unusual environmental settings where cellular remains and soft tissues can be preserved. Consequently, researchers know very little about how life was evolving across a period that makes up 90% of Earth's history.
As for Anderson?
"I'm interested in how we went from a planet that just had bacteria to one that had complex multicellular organisms," Anderson said. "Those kinds of multicellular fossils are hard to find, so I do a lot of work on the chemistry of the rocks to find out in which settings they are preserved."
One problem is that eukaryotic microfossils are subject to billions of years of degradation.
"But we know that the transition from single-celled to multicellular happened multiple times in different parts of the Earth," Anderson said. "We're interested in how animals became so diverse today."
Most of their diversity was established across the Ediacaran–Cambrian transition. That was about 540 million years ago and represented a major evolutionary step between soft-bodied biota and the Cambrian explosion of life with mobility, shells and skeletons.
As for where to look for such ancient eukaryotic microfossils?
Anderson and colleagues are particularly interested in a 100-square-kilometer (39-square-mile) area in what was a shallow sea at about 80 degrees north, in a remote group of islands near Svalbard, Norway.
And just last year, researchers in Australia found some of the oldest eukaryote microfossils ever discovered, dating back some 1.75 billion years.
The sweet spot for such microfossils is usually in ancient coastal areas, where eukaryotes would have had access to rich organic material and plentiful nutrients, enabling them to grow in both multicellularity and diversity.
The idea is to go to areas that are either pristine or have not been sampled to any great extent. Anderson specializes in looking in areas where massive clay deposits might have helped preserve these ancient eukaryotes.
"Today, you're looking at places that are desert or Arctic, where there's no vegetation, so rocks are exposed," Anderson said.
None of which is easy. Looking for eukaryote microfossils is a Herculean task because they are both tiny and consist of unprotected soft tissue, leaving them subject to massive degradation over billions of years.
"The biggest challenge now is that we have an undersampled fossil record," Anderson said.
Are we any closer to answering the big questions about how complex life first started here?
"We've started to figure out which are the right rocks in which to find early fossils, and that's starting to give us the data with which we can record the history of Earth's earliest life," Anderson said.
The bottom line?
"A lot of the work we've done on clays was motivated by finding life on other planets," Anderson said. "We'd better understand how life happened here if we hope to understand the likelihood of it happening elsewhere."
Who's behind this story?
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Citation: On the hunt for Earth's first complex life (2026, July 20) retrieved 20 July 2026 from https://phys.org/news/2026-07-earth-complex-life.html
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