TOM LEONARD: Could life on Earth have arrived on an asteroid 3.8 billion years ago?
Could life on Earth have arrived on an asteroid 3.8 billion years ago? As scientists discover intriguing new DNA in meteorite samples, TOM LEONARD examines the mind-boggling possibilities
From the rocks found in Native American burial sites to the sacred stone that “fell from Jupiter” and was consecrated at the Temple of Artemis in Ephesus – one of the Seven Wonders of the Ancient World – there is evidence to show that the early civilizations were worshiped and perhaps even meteorites revered.
Since they had literally fallen from the sky, it was inevitable that some would consider them gifts from the gods.
And it’s increasingly appearing that the Ancients may have understood something by attaching some primary meaning to those chunks of stone or metal from interplanetary space that survive passing through Earth’s superheated atmosphere before breaking through. crush on our planet.
New research by Japanese scientists suggests that such cosmic impacts may have provided Earth with the chemical ingredients needed for life itself to begin.
Not so much a Big Bang as a Heavy Thud, then, like billions of years ago, a huge space rock – which just happened to contain the building blocks of DNA – landed on a lifeless Earth.
DNA, of course, carries the genetic instructions for all living organisms.
New research by Japanese scientists suggests that such cosmic impacts may have provided Earth with the chemical ingredients needed for the start of life itself.
And Panspermia, they say, could also work the other way around, so meteorites from Earth seeded life on other planets. For decades, panspermia has been dismissed by many experts as dubious pseudo-science.
Our planet formed about 4.5 billion years ago, but the precise origins of life here have long puzzled experts. Early in its existence, the Earth was bombarded by meteorites, comets and other material from space, and was probably too hot for life to exist until about four billion years ago.
The first organisms were primitive microbes that thrived in oceans rich in organic matter, the “primordial soup” of our origins, which allowed various chemical compounds to bond and evolve to the point where they could use sources of water. energy – like sunlight and water – to form a living microbe that could replicate.
The formation of DNA (and its sister molecule, RNA) would have marked a crucial step in this process.
Although the earliest known fossils are marine specimens that date back approximately 3.5 billion years, there are suggestions of life on Earth dating back 3.8 billion years.
Since Earth was considered uninhabitable until just 0.2 billion years earlier – a relatively short period in the planet’s history – some scientists have argued that the probability of life based on the DNA evolving so early indicates that she got a helping hand, so to speak, from somewhere else.
Proponents of a hypothesis known as Panspermia believe that ‘life’ was shared via meteorites traveling from one planet to another, or was brought by a comet or space dust.
They argue that terrestrial life originated elsewhere in the Universe, even before the formation of the Earth, and was seeded here by a meteorite, possibly by the start of Martian life, as it is increasingly accepted that Mars was probably more habitable than Earth early in its history.
And Panspermia, they say, could also work the other way around, so meteorites from Earth seeded life on other planets.
For decades, panspermia was dismissed by many experts as dubious pseudo-science.
However, that is no longer the case and a team of leading scientists from Harvard and the Massachusetts Institute of Technology (MIT) spent a decade, funded by NASA, designing a device that could be sent to Mars to search for DNA and RNA. .
The team examined material from three meteorites – one that fell in 1950 near the town of Murray in the US state of Kentucky, one that landed in 1969 near the town of Murchison in the Australian state of Victoria and one that arrived in 2000 near Tagish Lake in British Columbia, Canada
However, the main stumbling block to the hypothesis that life arrived after hitching a ride on a meteorite was that only two of the four major DNA components had been found in space rocks. A crucial third component – found in RNA – was also missing.
Not anymore, according to scientists from the Japanese universities of Hokkaido and Kyushu. In a report published in the journal Nature Communications, they describe how they carried out a sophisticated new analysis of meteorites that had landed in the United States, Canada and Australia.
While the previous examination of meteorites had used strong acids and heat to extract DNA components (known as nucleobases), the team led by astrochemist Yasuhiro Oba used more sensitive techniques. with ultra-high resolution equipment.
Their research showed that there are indeed tiny amounts of missing nucleobases – called pyrimidines – in space rocks.
They may have escaped detection in previous examinations because they possess a more delicate structure than other nucleobases, the Japanese researchers concluded.
The team examined material from three meteorites – one that fell in 1950 near the town of Murray in the US state of Kentucky, one that landed in 1969 near the town of Murchison in the Australian state of Victoria and one that arrived in 2000 near Tagish Lake in British Columbia, Canada.
The 220-pound Murchison meteorite was recently identified as containing the oldest material on Earth – seven billion-year-old stardust.
All three meteorites are classified as carbonaceous chondrites, made up of rocky material thought to have formed early in the solar system’s history. They are rich in carbon and carbon is a main constituent of organisms on Earth.
However, the main stumbling block to the hypothesis that life arrived after hitching a ride on a meteorite was that only two of the four major DNA components had been found in space rocks. A crucial third component – found in RNA – was also missing
“The presence of the five primary nucleobases in meteorites may have contributed to the emergence of genetic functions before life appeared on early Earth,” said Yasuhiro Oba.
“The absolute abundance of nucleobases of extraterrestrial origin could be sufficient for other chemical reactions on early Earth.”
Danny Glavin of NASA’s Goddard Space Flight Center and co-author of the study, said the research “certainly adds to the list of chemical compounds that would have been present in the prebiotic soup of early Earth (existing before the emergence of life).
Other scientists are also encouraged. “It’s one of the last ingredients on the list that we need to show that we were created in space,” said Professor Mark Sephton, an astrobiologist at Imperial College London.
He told the Mail: ‘Meteorites are time capsules that record events that happened before planets were formed. Thus, the first chemical steps towards life may have taken place before the Earth existed.
We are very fortunate that nature provides us with these very ancient samples that provide a window into conditions and events billions of years ago.
The Japanese study certainly gives a major boost to the panspermia hypothesis. Proponents hope further confirmation will come when scientists can examine samples taken from two large asteroids, Ryugu and Bennu, by spacecraft developed by NASA and the Japanese space agency JAXA.
The possibility that the ingredients for life are floating around in space waiting to find a planet with the right conditions is mind-boggling. Even more, surely, is the idea that our own planet may have already seeded life elsewhere in the Universe.
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