Scientists say they have found fossilized evidence for some of the oldest life on Earth, dating back 3.95 billion years into our planet’s history.
The research, published in Nature, was led by the University of Tokyo in Japan. The team analyzed sedimentary rocks – formed by sediments settling at the bottom of the ocean – in northern Labrador, Canada.
The groundbreaking discovery pushes the earliest date life emerged on Earth back 150 million years, as previous evidence of life dates to 3.8 billion years ago. This was a time in history when our planet was still being pounded by asteroids, known as the Late Heavy Bombardment period.
“Our discovery substantially broke the record of the earliest life on Earth,” Tsuyoshi Komiya from the University of Tokyo, a co-author of the study, told IFLScience. “This information helps the study of early life and the origin of life.”
The team discovered evidence of simple life by looking at graphite inside metasedimentary rocks that have been heated or subjected to high pressure. Studying the graphite, the researchers found evidence that it was biogenic, meaning it was produced by life. A lack of inconsistencies between the temperatures of the graphite and the surrounding rock suggests this was not a result of later contamination.
We don’t know for sure what organism was responsible, but it’s possible the graphite was produced by some sort of single-celled organism capable of photosynthesis. Complex life probably did not arise until about 800 million years ago, after photosynthetic life had oxygenated our atmosphere.
“Early life possibly had a simple morphology, indistinguishable from inorganic products,” said Komiya.
While this is evidence of life, it is not a direct discovery of life. Further study will be needed to find out what organisms produced the graphite. But the discovery is hugely important by itself, as it pushes back when life on our planet began.
Discovering evidence of life early in Earth’s history is difficult, not least because rocks dating back this far are hard to find. The oldest rock on Earth is known as the Acasta Gneiss Complex, also in Canada and dating back 4.03 billion years. But as these rocks first originated in a deep magma chamber, and were then subjected to high pressures and temperatures, life isn't expected to be found within them.
This latest discovery is, therefore, pushing the limits of how far back into our planet’s history we can look. It doesn’t just have implications for life here, but life on other worlds too.
Mars and Venus in our Solar System were both thought to have hosted oceans at some point billions of years ago, with conditions not too dissimilar to Earth. If life was able to start on our planet around that time, could it have started elsewhere?
“The discovery of the biogenic graphite enables geochemical study of the biogenic materials themselves, and will provide insight into early life not only on Earth but also on other planets,” the team noted in their paper.