Life on Earth may have sparked into existence as early as 4.4 billion years ago, hundreds of millions of years earlier than previously thought possible, a study to be published today says.
Until now scientists assumed that no life forms could have survived the so-called Late Heavy Bombardment, a 100-million-year fusillade during which our young planet was pummeled by meteorites that blasted craters the size of Thailand and France.
All told, some 2 quadrillion tonnes of space rock rained down on the planet, the new study says.
Heat generated by this relentless pounding was intense enough to melt much of Earth’s surface, rendering it uninhabitable even for primitive life forms that thrived at high temperatures.
That, at least, has been the conventional wisdom, bolstered by the fact that the earliest traces of life discovered so far appeared shortly after the extraterrestrial onslaught tapered off 3.9 billion years ago.
Fossils reveal microscopic life forms 3.5 billion years old, and geochemical clues point to more primitive organisms — thought by some to be the common ancestor to all things living — 300,000 million years before that.
But Stephen Mojzsis and Oleg Abramov of the University of Colorado argue that early Earth wasn’t so hellish after all.
Many life forms that might have arisen earlier could well have survived the bombardment, according to their study, published in Nature.
Using numerical models of impact-generated heat in Earth’s crust, they show that no more than 37 percent of the planet’s surface was sterilized at any given time, and that only 10 percent reached temperatures above 500°C.
That is very hot, but much of Earth was cool enough to accommodate different families of microbes able to take the heat, 20°C to 50°C for some, and beyond the boiling point — up to 110°C — for others.
Some microbes would also have been able to live several kilometers below Earth’s surface, much as some simple life forms do today, the study points out.
“Our analysis shows that there is no plausible situation in which the habitable zone was fully sterilized on Earth,” Mojzsis said.
“All the criteria necessary for life” — liquid water, energy sources such as sunlight and chemical building blocks from meteors or Earth itself — “were present at least since 4.38 billion years ago,” he said by e-mail.
“The antiquity of life may not be very much less than the Earth itself,” he said.
Research published last week shows how a series of chemical reactions on early Earth could have produced ribonucleic acid, or RNA, a single-stranded cousin of the DNA that is the blueprint for all life.
Pushing back the date at which self-replicating life forms first emerged from the primordial soup would also explain how the relatively complex organisms that fossils records show existed 3.5 to 3.8 billion years ago could have had time to evolve.
In a commentary, also published in Nature, Lynn Rothschild of the NASA Ames Research Center in California says the new study convincingly shows how life may have emerged sooner rather than later.
“Moreover, it opens the possibility that life arose on Earth only once, and that the planet has been continuously inhabited ever since,” she said.
Mojzsis is less inclined to think that everything within the realm of biology can be traced back to a single so-called “last universal common ancestor.”
“Instead, they might have been a community of co-evolving proto-organisms that crystallized into a population” of primitive cells, he said.
Answering once-and-for-all the question of whether life happened more than 4 billion years ago will be extremely difficult, scientists say. So much of the evidence — if there is any — was destroyed during Earth’s fiery baptism that finding intact traces may be futile. The earliest sedimentary rock ever found is “only” 3.83 billion years old.
‘IN A DIFFERENT PLACE’: The envoy first visited Shanghai, where he attended a Chinese basketball playoff match, and is to meet top officials in Beijing tomorrow US Secretary of State Antony Blinken yesterday arrived in China on his second visit in a year as the US ramps up pressure on its rival over its support for Russia while also seeking to manage tensions with Beijing. The US diplomat tomorrow is to meet China’s top brass in Beijing, where he is also expected to plead for restraint as Taiwan inaugurates president-elect William Lai (賴清德), and to raise US concerns on Chinese trade practices. However, Blinken is also seeking to stabilize ties, with tensions between the world’s two largest economies easing since his previous visit in June last year. At the
Nearly half of China’s major cities are suffering “moderate to severe” levels of subsidence, putting millions of people at risk of flooding, especially as sea levels rise, according to a study of nationwide satellite data released yesterday. The authors of the paper, published by the journal Science, found that 45 percent of China’s urban land was sinking faster than 3mm per year, with 16 percent at more than 10mm per year, driven not only by declining water tables, but also the sheer weight of the built environment. With China’s urban population already in excess of 900 million people, “even a small portion
UNSETTLING IMAGES: The scene took place in front of TV crews covering the Trump trial, with a CNN anchor calling it an ‘emotional and unbelievably disturbing moment’ A man who doused himself in an accelerant and set himself on fire outside the courthouse where former US president Donald Trump is on trial has died, police said yesterday. The New York City Police Department (NYPD) said the man was declared dead by staff at an area hospital. The man was in Collect Pond Park at about 1:30pm on Friday when he took out pamphlets espousing conspiracy theories, tossed them around, then doused himself in an accelerant and set himself on fire, officials and witnesses said. A large number of police officers were nearby when it happened. Some officers and bystanders rushed
Beijing is continuing to commit genocide and crimes against humanity against Uyghurs and other Muslim minorities in its western Xinjiang province, U.S. Secretary of State Antony Blinken said in a report published on Monday, ahead of his planned visit to China this week. The State Department’s annual human rights report, which documents abuses recorded all over the world during the previous calendar year, repeated language from previous years on the treatment of Muslims in Xinjiang, but the publication raises the issue ahead of delicate talks, including on the war in Ukraine and global trade, between the top U.S. diplomat and Chinese