Old rocks yield new clues: Researchers discover oldest records of life on Earth
What are the origins of life on Earth? The question has puzzled generations of scientists around the world and remains a topic of ardent debate. As our planet morphed over billions of years from magma oceans to Earth as we know it today, pinpointing the origins of the first life forms would provide a crucial piece of the puzzle to explain the remarkable history of the evolution of life and yield clues to finding traces of life on other planets.
An international team of scientists has made a discovery that pushes back the oldest traces of life by about 100 million years, and possibly by more than 600 million years, in a study published today in Nature. The team turned to some of the oldest rocks on Earth to search for evidence of life, focusing their attention on rocks called banded iron formations from an area known as the Nuvvuagittuq Greenstone Belt in Northern Quebec. Work by Jonathan O’Neil, of the University of Ottawa’s Department of Earth and Environmental Sciences, shows that these rocks are at the very least 3.8 billion years old, though more likely 4.3 billion years old, making them the oldest on the planet.
The Nuvvuagittuq Greenstone Belt represents what would have been the earliest oceanic crust formed on Earth. Encased in quartz layers of its banded iron formations, the team found remains of microorganisms—tiny filaments and tubes formed by bacteria that lived on iron. “Our study shows that some structures in these rocks are consistent with being fossilized microorganisms. They would be the oldest microfossils ever found and therefore the oldest record of life on Earth,” explains O’Neil. “The findings support the theory that life emerged from hot, sea floor vents shortly after the formation of Earth.”
Prior to this study, the oldest evidence of life was determined to be about 3.5 billion years old, though recent studies have suggested the presence of stromatolites (sedimentary rocks formed from the growth of cyanobacteria) dated back about 3.7 billion years.
To give an idea of the microfossils’ age, scientists estimate that Earth was “born” more than 4.5 billion years ago as gases and matter from exploding stars, called supernovae, condensed and accreted (grew by accumulation) to form the Sun and our solar system. It was during that time that a violent impact between the early Earth and another planetary object ejected debris that would later become the Moon.
Researchers are still piecing together information on what the Earth looked like during the lifetime of the microfossils discovered by O’Neil and his team and during the earliest era of the planet’s existence. “The rare rocks and minerals dated from that period give us a portrait of a world composed of volcanic islands and shallow oceans, with perhaps already small continents,” notes O’Neil. It then took more than three billion years for the first multi-celled animals to appear, about 600 million years ago, in an environment far more similar to today’s.
The ancient oceanic crust from the Nuvvuagittuq Greenstone Belt was dated at nearly 4.3 billion years old using techniques that have never before been used on terrestrial rocks because they can only be applied on objects older than 4 billion years old, such as meteorites. With the exception of the Nuvvuagittuq Greenstone Belt, rocks found on Earth are too “young” to be dated with that technique. This old age remains debated, but zircons dated using conventional techniques on rocks intruding the Nuvvuagittuq oceanic crust puts its age at minimum of 3.8 billion years old.
“The discovery will help further our understanding of when and perhaps how life began on Earth. It also shows that the right conditions for the emergence of life were already established on Earth very early on,” says O’Neil. “If we better understand the environments in which life started on Earth, this could help us tackle questions about possible life on other planets such as Mars.”
TIMELINE OF LIFE ON EARTH
- 4.568 billion years ago: Earth forms
- 4.3 to 3.8 billion years ago: Oldest life forms, identified by professor O’Neil’s team
- 600 million years ago: First multi-celled animals
- 385 million years ago: Oldest fossilized tree
- 230 million years ago: Dinosaurs appear
- 65 million years ago: Extinction of dinosaurs enables mammals to flourish
- 6 million years ago: Humans split from apes and start walking on two legs
Members of the research team
Matthew Dodd, Martin Rittner and Dominic Papineau (University College London); Jonathan O’Neil (University of Ottawa); Tor Grenne (Geological Survey of Norway); Franco Pirajno (University of Western Australia); John Slack (US Geological Survey) and Crispin Little (University of Leeds)
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