Latest chemical ingredients to make human DNA discovered in meteorites. This is what we know

A new survey of meteorites that have landed in Australia, the US, and Canada confirms that such objects early in Earth’s history may have provided chemical ingredients vital to the arrival of life.

Scientists had previously discovered three of the five chemical components needed to form DNA on meteors — and last week, they found the previous two.

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

Researchers say they have identified the latter two after refining how they analyzed the meteorites.

The new research results have been published in Nature Communications, featuring new methods described by study leader astrochemist Yasuhiro Oba of the Hokkaido University Institute of Low-Temperature Science.

Unlike previous work, Oba said the methods used this time were more sensitive and didn’t use strong acids or hot liquid to extract the five components, known as nucleobases.

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 confirms that such objects early in Earth’s history may have provided chemical ingredients vital to the arrival of life. Credit: Brian Cassella/Delivered

Confirmation of an extraterrestrial origin of a complete set of nucleobases found in DNA and RNA supports the theory that meteorites may 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 Goddard Space Flight Center astrobiologist Danny Glavin.

Scientists have been trying to understand better what happened on Earth, which caused various chemical compounds to come together in a warm, watery environment to form a living microbe that could reproduce itself.

The formation of DNA and RNA would be an important milestone, as these molecules essentially contain the instructions to build and operate living organisms.

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“There is still much to learn 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 the early Earth (which existed before the emergence of life).”

The researchers examined material from three meteorites — one that fell in 1950 in the US state of Kentucky, one that fell in 1969 near the city of Murchison in Victoria, Australia, and one that fell in 2000 at Tagish Lake in the Canadian province of British Columbia.

All three are classified as carbonaceous chondrites, made of rocky material believed to have formed early in the solar system’s history.

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They are carbon-rich, with the Murchison and Murray meteorites containing about 2 percent organic carbon and the Tagish Lake meteorite about 4 percent organic carbon. Carbon is a main component of organisms on Earth.

“All three meteorites contain a very complex mixture of organic molecules, most of which have not yet been identified,” Glavin said.

The Earth formed about 4.5 billion years ago. It was pelted by meteorites, comets, and other materials from outer space in its infancy.

The planet’s first organisms were primitive microbes in the ancient seas, and the earliest known fossils are marine microbial specimens dating to about 3.5 billion years ago. However, there are hints of life in older fossils.

The researchers said the two nucleobases, called cytosine and thymine, newly identified in the meteorites may have escaped detection in previous studies because they have a more delicate structure than the other three.

The five nucleobases would not be the only chemical compounds necessary for life.

Needed were, among other things: 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 explain 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 the start of life.”