Traditional scientific theories claim that life on our planet began only long after the Earth itself was formed. However, a group of geochemists at the University of California, Los Angeles (UCLA) believes that the first living organisms could have appeared as early as 4.1 billion years ago - shortly after the formation of the planet.
Zircons and the history of the Earth
For quite a long time it was believed that the young Earth was a barren desert, on which there was no place for life. It was only about 3.8 billion years ago that conditions became favorable enough for the emergence of living organisms.
However, recent studies show that life on our planet existed even before the solar system was subjected to internal asteroid bombardment, which is today reminiscent of giant craters aged 3.9 billion years.
"If all life on Earth died during this bombing, as some scientists say, then life should have quickly reincarnated," says one of the co-authors of the new study, graduate student Patrick Bene.
Meanwhile, a team from UCLA has found evidence that life was present on Earth at least 4.1 billion years ago. Geochemistry professor Mark Harrison and his colleague, professor of geology and geochemistry Craig Manning, in collaboration with former UCLA graduate student Michelle Hopkins, published an article in the journal Nature back in 2008, in which they prove their theory.
Researchers have studied more than 10,000 zircon samples formed from molten volcanic rocks in Western Australia at the dawn of the planet's formation. The ratio of carbon-12 to carbon-13 in these stones indicates the presence of photosynthetic life.
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After isolating 656 samples with dark specks, the scientists subjected 79 of them to Raman spectroscopy, a technique that allows you to see the molecular and chemical structure of ancient microorganisms in a 3D model. It turned out that one of the samples in two places has inclusions of graphite - pure carbon. The mineral's ratio of uranium to lead helped determine its age - 4.1 billion years. But graphite may be older than the rest.
“This is the best documented case of direct inclusion in the mineral, and no one has yet proposed a viable alternative explanation for this non-biological graphite in zircon,” says Harrison.
How the processes of evolution went
According to the scientist, life on Earth can exist everywhere, and it does not take long for it to arise. In all likelihood, the simplest organisms appeared on Earth almost immediately after it was formed, but it took many millions of years for them to develop the ability to photosynthesize, so that they could directly use solar energy.
This contributed to the filling of the atmosphere with oxygen (which happened about 2.5 billion years ago) and the formation of the ozone layer, which absorbs harmful ultraviolet radiation.
Further, the processes of symbiosis of small cells with larger ones led to the development of more complex living cells - eukaryotes. Multicellular organisms arose about 2.1 billion years ago. The process of adaptation to environmental conditions was actively continued.
The first algae appeared on Earth about 1200 million years ago, and higher plants appeared 450 million years ago. The appearance of the first invertebrates belongs to the Ediacaran period (541-635 million years ago), and the appearance of the first vertebrates - to the Cambrian explosion (525 million years ago). After that, life continued to evolve continuously, despite several periods of mass extinction due to various cataclysms that shook the planet.
Has the earth never been lifeless?
“Twenty years ago it would have been considered heresy; to find evidence of life as old as 3.8 billion years old was a shock, commented Harrison. - Life on Earth could begin almost immediately. Given the right ingredients, life seems to form very quickly.”
Elizabeth Bell, who is also involved in the study, believes that the Earth was not initially so dry at all, the conditions on it were much closer to the present than you might imagine. So you can forget about the theory of a "lifeless planet".
IRINA SHLIONSKAYA