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.
An endangered baby pygmy hippopotamus that shot to social media stardom in Thailand has become a lucrative source of income for her home zoo, quadrupling its ticket sales, the institution said Thursday. Moo Deng, whose name in Thai means “bouncy pork,” has drawn tens of thousands of visitors to Khao Kheow Open Zoo this month. The two-month-old pygmy hippo went viral on TikTok and Instagram for her cheeky antics, inspiring merchandise, memes and even craft tutorials on how to make crocheted or cake-based Moo Dengs at home. A zoo spokesperson said that ticket sales from the start of September to Wednesday reached almost
TIGHTENING: Zhu Hengpeng, who worked for an influential think tank, has reportedly not been seen in public since making disparaging remarks on WeChat A leading Chinese economist at a government think tank has reportedly disappeared after being disciplined for criticizing Chinese President Xi Jinping (習近平) in a private chat group. Zhu Hengpeng (朱恆鵬), 55, is believed to have made disparaging remarks about China’s economy, and potentially about the Chinese leader specifically, in a private WeChat group. Zhu was subsequently detained in April and put under investigation, the Wall Street Journal reported. Zhu worked for the Chinese Academy of Social Sciences (CASS) for more than 20 years, most recently as the Institute of Economics deputy director and director of the Public Policy Research Center. He
CHINESE ICBM: The missile landed near the EEZ of French Polynesia, much to the surprise and concern of the president, who sent a letter of protest to Beijing Fijian President Ratu Wiliame Katonivere called for “respect for our region” and a stop to missile tests in the Pacific Ocean, after China launched an intercontinental ballistic missile (ICBM). In a speech to the UN General Assembly in New York on Thursday, Katonivere recalled the Pacific Ocean’s history as a nuclear weapons testing ground, and noted Wednesday’s rare launch by China of an ICBM. “There was a unilateral test firing of a ballistic missile into the Pacific Ocean. We urge respect for our region and call for cessation of such action,” he said. The ICBM, carrying a dummy warhead, was launched by the
As violence between Israel and Hezbollah escalates, Iran is walking a tightrope by supporting Hezbollah without being dragged into a full-blown conflict and playing into its enemy’s hands. With a focus on easing its isolation and reviving its battered economy, Iran is aware that war could complicate efforts to secure relief from crippling sanctions. Cross-border fire between Israel and Hezbollah, sparked by Hamas’ attack on Israel on Oct. 7 last year, has intensified, especially after last week’s sabotage on Hezbollah’s communications that killed 39 people. Israeli airstrikes on Hezbollah strongholds in Lebanon followed, killing hundreds. Hezbollah retaliated with rocket barrages. Despite the surge in