The emergence of life on Earth is a hotly debated topic in the scientific realm. When precisely did the chemistry of the world give rise to biology? A new study, published in the journal Proceedings of the National Academy of Sciences, provides compelling evidence that life started 4.1 billion years ago, 300 million years earlier than previously thought.
The research team, led by the University of California, Los Angeles (UCLA), looked inside 79 zircon crystals in Western Australia, and found that just one of them contained an unexpected substance. Zircons are among the oldest material on Earth, forming as a mineral within certain magmas as they cool. As they are incredibly durable, with a strong resistance to corrosion or temperature changes, they act as time capsules, preserving the conditions around the moment of their crystallization.
This single 4.1-billion-year-old zircon contained graphite, a form of carbon – the element all life on Earth is based on. When this was chemically analyzed, the researchers discovered to their shock that it was enriched with carbon-12, a lighter version of carbon associated with life.
Until now, the scientific consensus was that life could only have started after the Late Heavy Bombardment (LHB), an ancient time when the Earth experienced a prolonged series of impacts. The Earth, violently volcanic and at the end of a planetoid shooting gallery, was thought to be far too hostile back then for the planet’s chemistry to be able to transition into hereditary material, likely DNA, which at some point replicated enough to form life in a process known as abiogenesis.
Life on Earth was, until now, thought to have begun around 3.8 to 3.5 billion years ago. Although there are some possible earlier chemical signatures of it, the first fossilized evidence came from some heavily deformed, 3.7-billion-year-old rocks in Greenland, which also showed traces of the light carbon-12 element within graphite. Ruling out that this carbon was not formed by geological processes, researchers thought that this was the first preserved evidence of life on Earth. Either way, by at least 3.5 to 3 billion years ago, there was ample fossil or chemical evidence that simple cells, some of which were using a primitive form of photosynthesis, were around.
This new finding, which the researchers have high confidence in, suggests that life started immediately after the LHB, and only 450 million years after Earth itself was forged in the fires of our young Solar System.
“Twenty years ago, this would have been heretical; [back then,] finding evidence of life 3.8 billion years ago was shocking,” said Mark Harrison, co-author of the research and a professor of geochemistry at UCLA, in a statement. “Life on Earth may have started almost instantaneously. With the right ingredients, life seems to form very quickly.”
With the exception of some viruses, the DNA of all life on Earth shares four bases – chemical building blocks that make up our DNA strands. This universal feature strongly suggests that the event that first synthesized DNA only happened once, or that any other synthesizing attempts were terminated. If life began 4.1 billion years ago, this means that DNA itself began to replicate even earlier, perhaps at the end of the LHB.
Everything living on planet Earth began with this rare synthesis event, traced back to right near the beginning of the world. Darwin would have loved this.