By Will Howell
Researchers have discovered evidence that evolutionary elements did not come to Earth until much later in its formation, contradicting previous theories about their presence on our planet.
Water, as well as the elements carbon and nitrogen, are currently thought to have arrived on Earth from asteroids during Earth’s formation. These asteroids are known as ‘planetary building blocks’ as planets form due to space debris and gas pulling together and growing larger. With increased size comes stronger gravitational force, leading to larger objects such as asteroids being pulled into the mix, forming planets. It was this method that was previously thought to have brought these fundamental elements and compounds to Earth.
But new evidence suggests this did not occur until much later in the planet’s development. A team of geologists, led by scientists at the University of Cologne and including a researcher from Cardiff University have found new evidence that narrows down the timeframe of when this might have happened, allowing a glimpse into Earth’s ancient past.
The researchers analysed ruthenium, a platinum-group metal, in the oldest mantle rock (the layer of rock between the crust and outer core of Earth) on the planet. Found in Greenland, these rocks are dated to the ‘Archean Eon’ over 3.8 billion years ago, while the Earth itself is estimated to be some 4.54 billion years old. By analysing the isotopes found in the rocks, scientists can tell how long ago the ‘volatile’ elements and compounds arrived on Earth.
The isotopes measured found very little evidence of the volatiles, suggesting that the asteroids carrying them arrived later than previously thought.
Dr Mario Fischer-Gödde from the Institute of Geology and Mineralogy at the University of Cologne, the first author of the study said, “We have now been able to narrow down the timeframe much more precisely.”
Co-author of the study, Dr Wolfgang Maier from Cardiff University’s School of Earth and Ocean Sciences, added “Our results are surprising because the scientific community had previously assumed that water-bearing planetary building blocks were delivered to Earth during the earliest stages of its formation.”
These findings have important ramifications for theories about the evolution of life on Earth, as well as other planets. Professor Martin Van Kranendonk of the University of New South Wales explained “The results show that Earth did not really become a habitable planet until relatively late in its accretionary history.
“If you combine this with the evidence for very ancient life on Earth, it reveals that life got started on our planet surprisingly quickly, within only a few hundred million years. Now this might sound like a lot of time, and it is, but it is far different from what we used to think, that life took half a billion, or even a billion years to get started.
“And this gives hope for finding life on other planets that had a shorter geological history and period of ‘warm and wet’ conditions than Earth, because if life could get started quickly here, then perhaps it got started quickly elsewhere.”