Theoretical origin of life; new earliest? More comment (Introduction)

by David Turell , Monday, October 02, 2017, 23:21 (2609 days ago) @ David Turell

Even though there are new arguments against the early life interpretation, it appears most likely that life began earlier than thought until recently:

https://www.newscientist.com/article/2149168-life-may-have-begun-millions-of-years-earl...

"Ben Pearce of McMaster University in Hamilton, Ontario, Canada, and colleagues simulated conditions on early Earth to find out how readily the key molecules of life could have formed. They focused on “warm little ponds” on land, which are one of the suspected sites of the origin of life – the other being deep-sea vents.

"Pearce tackled the formation of RNA, a close cousin of DNA that is widely thought to have been the basis for the first life. Many of the building blocks of RNA are found in asteroids and meteoroids, so Pearce calculated how much could have been delivered to Earth by impacting rocks – of which there were plenty during Earth’s first billion years – and then how much could have accumulated in ponds, given the molecules’ fragility and tendency to leech away.

"He concluded that RNA could have formed within a handful of years of major impacts, implying that life could have formed very early in Earth’s history.

"There are two problems with this argument, says John Sutherland of the MRC Laboratory of Molecular Biology in Cambridge, UK.

"One is that organic compounds carried in meteorites would not necessarily survive the impact. “Large impactors that would have delivered the most organic material, collide with such energy that their organic cargo is atomised,” says Sutherland. (my bold)

" The other problem is that Pearce simulated the wrong chemical process, Sutherland says. Pearce assumed that the first step in making RNA is linking together smaller molecules called nucleobases and ribose, but this “was experimentally shown not to work ages ago”, says Sutherland. In 2009 Sutherland demonstrated an alternative way of making RNA from simpler building blocks. “These authors are still assuming the old model,” he says.

"A second study, published last Wednesday, claims to have identified the oldest firm evidence of life – dating back 3.95 billion years. That is only half a billion years after the Earth formed. Reliable fossils of microorganisms have been dated to roughly 3.5 billion years ago, but the evidence for older life has been less clear.

"Tsuyoshi Komiya of the University of Tokyo, Japan, and colleagues studied graphite found in ancient rocks in northern Labrador, Canada. Graphite is a crystalline form of carbon used to make pencil leads. It contains two forms of carbon: carbon-12 and carbon-13. The samples Komiya looked at had relatively little carbon-13. This, the team claims, is evidence that life was present. And not just any life: organisms that were taking in carbon from their surroundings and using it as raw material to make new organic compounds.

"This result is surprising for several reasons. First, at this time, Earth was being bombarded by large rocks from space, which would have battered the young planet’s surface. If life was present, it must have been impressively resilient.

"But only if Komiya’s study is correct. His only evidence for the existence of life is the unusual ratio of carbon isotopes, and this may not be definitive. “There are many ways in which abiotic processes can produce such an imbalance, so to conclude that it is evidence for life is simply not justified,” says Sutherland.

"Sutherland says a set of chemical reactions known as the Fischer-Tropsch process could be responsible. This process makes organic compounds from hydrogen and carbon monoxide, and show a similar bias towards carbon-12. It is known to occur naturally, for instance in meteorites.

"Komiya’s team assumed these reactions were not responsible for their results, on the grounds that there cannot have been hydrogen in Earth’s atmosphere. But Sutherland says there could well have been. If there was water and carbon monoxide in the air, and hot iron from meteorite impacts to act as a catalyst, “hydrogen can easily be generated”.

"Nevertheless, evidence is mounting that life was present earlier than 3.5 billion years ago. For instance, in 2016 fossilised stromatolites – layered mounds made by microbes living in sediments – were controversially claimed to have been found in 3.7-billion-year-old rocks. Then in March 2017, researchers described apparent fossilised microbes from rocks that were 3.77 to 4.28 billion years old. That claim also divided opinion."

Comment: No question life appeared very early under severe early Earth conditions. Not by chance, as there were so many problems to overcome. Note my bold about meteorites destroying any organic cargo. It must be God at work.