Final chemical ingredients to make human DNA discovered in meteorites. Here’s what we know

A new examination of meteorites that have landed in Australia, the United States and Canada reinforces the notion that, early in Earth’s history, such objects may have delivered vital chemical ingredients for the advent of life.

Scientists had previously detected three of the five chemical components needed to form DNA on meteors – and last week discovered the final two.

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Scientists previously knew about the molecule that carries genetic instructions in living organisms, and RNA, the crucial molecule for controlling the actions of genes.

The researchers say they have now identified the latter two after refining the way they analyze meteorites.

The new results of the study have been published in the journal Nature Communicationwith new methods detailed by study leader Yasuhiro Oba, an astrochemist at Hokkaido University’s Institute of Low-Temperature Science.

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, known as nucleobases, Oba said.

Nucleobases are nitrogen-containing compounds crucial in forming the characteristic double helix structure of DNA.

A new examination of meteorites that have landed in Australia, the United States and Canada reinforces the idea that early in Earth’s history such objects may have delivered vital chemical ingredients for the advent of life. Credit: Brian Cassel/Provided

The 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 of the Earth, according to study co-author and NASA Goddard Space Flight Center astrobiologist Danny Glavin.

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 because these molecules basically 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 prebiotic soup of early Earth (existing before the emergence of life).”

Researchers examined material from 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 of Lake Tagish in the Canadian province of British Columbia.

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 material 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 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.

“Current findings may not directly elucidate 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.”