A new examination of meteorites landed in Australia, the United States and Canada is reinforcing the idea that, early in Earth’s history, such objects may have provided vital chemical ingredients for the advent of life.
Scientists had previously detected three of the five chemicals needed to form DNA on meteorites, and last week they discovered the last two.
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Previously, scientists were aware of the molecule that carries genetic instructions in living organisms and of RNA, the crucial molecule for controlling the actions of genes.
The researchers say they have now identified the latter two after fine-tuning how they analyzed meteorites.
The results of the new study were published in the journal Nature Communications, with new methods detailed by the leader of the study, astrochemist Yasuhiro Oba of the University of Hokkaido’s Institute of Low Temperature Sciences.
Unlike previous work, the methods used this time around were more sensitive and didn’t use strong acids or hot liquids to extract the five components, known as nucleobases, Oba said.
Nucleobases are nitrogen-containing compounds crucial in the formation of the characteristic double helix structure of DNA.
Confirmation of an extraterrestrial origin of a full set of nitrogenous bases found in DNA and RNA supports the theory that meteorites could have been an important source of organic compounds necessary for the emergence of Earth’s first living organisms, according to study co-author and NASA’s Goddard Space Flight Center astrobiologist Danny Glavin.
Scientists sought to better understand the events on Earth that allowed various chemical compounds to combine in a warm, watery environment to form a living microbe that could reproduce.
The formation of DNA and RNA would be an important milestone as these molecules essentially contain the instructions for building and operating living organisms.
“There is still a lot to learn about the chemical steps that led to the origin of life on Earth, the first self-replicating system,” said Glavin.
“This research certainly adds to the list of chemical compounds that would have been present in the prebiotic soup of the early Earth (existing before the emergence of life).”
The researchers examined the material of three meteorites: one that fell in 1950 in the US state of Kentucky, one that fell in 1969 near the town of Murchison in Victoria, Australia, and one that fell in 2000 near Tagish Lake in the Canadian province of British Columbia. .
All three are classified as carbonaceous chondrites, made of rock material thought to have formed early in the history of the solar system.
They are rich in carbon, with the Murchison and Murray meteorites containing about 2% organic carbon by weight and the Lake Tagish meteorite containing about 4% organic carbon. Carbon is a primary constituent of organisms on Earth.
“All three meteorites contain a very complex mixture of organic molecules, most of which have not yet been identified,” said Glavin.
The Earth formed about 4.5 billion years ago. In his childhood, he was struck by meteorites, comets and other material from outer space.
The planet’s earliest organisms were primitive microbes in primeval seas, and the earliest known fossils are marine microbe specimens dating back about 3.5 billion years, although there are traces of life in the earliest fossils.
The two nitrogenous bases, called cytosine and thymine, recently identified in meteorites may have escaped detection in previous exams because they possess a more delicate structure than the other three, the researchers said.
The five nitrogenous bases would not have been the only chemical compounds necessary for life.
Among other things, the following were needed: amino acids, which are components of proteins and enzymes; sugars, which are part of the backbone of DNA and RNA; and fatty acids, which are structural components of cell membranes.
“The current findings may not directly clarify the origin of life on Earth,” Oba said.
“But I believe they can improve our understanding of the inventory of organic molecules on early Earth before life began.”