A new examination of meteorites that have landed in the United States, Canada and Australia reinforces the idea that early in Earth’s history such objects may have delivered vital chemical ingredients for the advent of life.
Scientists had previously detected on these meteorites three of the five chemical components necessary for the formation of DNA, the molecule which carries the genetic instructions in living organisms, and RNA, the molecule crucial to control the action of genes . The researchers said on Tuesday they had now identified the latter two after refining the way they analyze meteorites.
Unlike previous work, the methods used this time were more sensitive and did not use strong acids or hot liquid to extract the five components, called nucleobases, according to astrochemist Yasuhiro Oba of the Institute of Low Temperature Sciences. from Hokkaido University in Japan, lead author of the study published in the journal Nature Communications.
Nucleobases are nitrogen-containing compounds crucial in forming the characteristic double helix structure of DNA.
Confirmation of an extraterrestrial origin of a complete set of nucleobases found in DNA and RNA reinforces the theory that meteorites could have been an important source of organic compounds necessary for the emergence of the first living organisms on Earth , according to astrobiologist and study co-author Danny Glavin of NASA’s Goddard Space Flight Center in Maryland.
Scientists sought to better understand the events that took place on Earth that allowed various chemical compounds to come together in a warm, watery environment to form a living microbe capable of reproduction. The formation of DNA and RNA would be an important step, as these molecules essentially contain the instructions to build and operate living organisms.
“Much remains to be learned about the chemical steps that led to the origin of life on Earth – the first self-replicating system,” Glavin said. “This research certainly adds to the list of chemical compounds that would have been present in the early Earth prebiotic [existing before the emergence of life] soup.”
Where the meteorites were found
Researchers examined material from three meteorites – one that fell in 1950 near the town of Murray in the US state of Kentucky; one which fell in 1969 near the town of Murchison in the State of Victoria in Australia; and one that fell in 2000 near Tagish Lake in British Columbia
On the morning of January 18, 2000, a blue-green fireball crossed the sky &; crashed into frozen Tagish Lake in northwest British Columbia. It was a stony meteorite (chondrite). The scanning electron microscope photo shows framboidal (resembling raspberries) crystals of magnetite. #ThrowbackThursday #tbt pic.twitter.com/yy9ReYgpUC
All three are classified as carbonaceous chondrites, made up of rocky material thought to have formed early in the solar system’s history. They are carbon-rich, with the Murchison and Murray meteorites containing about 2% organic carbon by weight and the Tagish Lake meteorite containing about 4% organic carbon. Carbon is a primary constituent of organisms on Earth.
“All three meteorites contain a very complex mix of organic molecules, most of which have yet to be identified,” Glavin said.
The Earth was formed about 4.5 billion years ago. In its early days, it was bombarded by meteorites, comets and other materials from space. The first organisms on the planet were primitive microbes in the primordial seas, and the earliest known fossils are marine microbial specimens dating back around 3.5 billion years, although there are hints of life in fossils older.
The 5 key ingredients
The two nucleobases, called cytosine and thymine, newly identified in meteorites may have escaped detection in previous examinations because they possess a more delicate structure than the other three, the researchers said.
The five nucleobases would not have been the only chemical compounds necessary for life. Among other things needed were: amino acids, which are components of proteins and enzymes; sugars, which are part of the DNA and RNA backbone; and fatty acids, which are structural components of cell membranes.
“The current results may not directly elucidate the origin of life on Earth,” Oba said, “but I believe they may improve our understanding of the inventory of organic molecules on early Earth before the onset of life.”