Could key ingredients for life have come from space?

The answer of scientists is "yes", Reuters reported. 

A new study of meteorites that fell in the United States, Canada and Australia confirms the idea that such celestial bodies may have delivered to Earth at the beginning of its history chemical ingredients vital to the emergence of life.

Scientists have previously discovered in these meteorites three of the five chemical components needed to form DNA - the molecule that carries genetic instructions in living organisms, and RNA - a molecule crucial for controlling the action of genes.

Researchers now say they have already identified the last two components after refining the way they analyzed the meteorites.

Scientists this time used more sensitive methods and did not use strong acids or hot liquid to extract the five components known as nucleobases, explains astrochemist Yasuhiro Oba of the University of Hokkaido in Japan, lead author of the study published in the journal Nature Communications. ". 

Nucleobases are nitrogen-containing compounds that are crucial for the formation of the characteristic double-stranded structure of DNA. 

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Confirmation of the extraterrestrial origin of the full range of nucleobases found in DNA and RNA supports the theory that meteorites could be an important source of organic compounds needed for the first living organisms on Earth, according to astrobiologist and co-author Danny Glavin of NASA's Goddard Space Flight Center in Maryland.

Scientists are trying to better understand the events that took place on Earth and allowed various chemical compounds to combine in a warm aquatic environment to form a living microbe capable of self-replicating.

The formation of DNA and RNA would be an important step, as these molecules essentially contain instructions for the construction and functioning of living organisms.

"There's still a lot to learn about the chemical steps that led to life on Earth - the first self-replicating system," says Glavin.

"This study certainly complements the list of chemical compounds that would be present in early prebiotic (pre-life) soup, also known as primary broth.

Scientists have studied material from three meteorites - one that fell in the United States in 1950 near Murray, Kentucky, the other - in 1969 near Murchison in the Australian state of Victoria, and the third - in 2000 near to Lake Tagish in the Canadian province of British Columbia.  

All three meteorites are classified as carbon chondrites, composed of rocky material believed to have formed early in the history of the solar system.

They are rich in carbon, with Murchison and Murray meteorites containing about 2 percent organic carbon by weight and Lake Tagish meteorite about 4 percent.

Carbon is a major component of Earth's organisms.

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

The earth was formed about 4.5 billion years ago.

In the beginning of its existence, our planet 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 of marine microbial specimens date back about 3.5 billion years, although older fossils suggest life.

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The two nucleobases, called cytosine and thymine, recently identified in the meteorites, may not have been found in previous studies because they have a more delicate structure than the other three, adenine, guanine and uracil, the researchers said. 

Scientists point out that two types of elements are needed for the formation of DNA and RNA - pyrimidines, including cytosine, uracil and thymine, and purines, containing adenine and guanine. 

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

Other essential ingredients included: amino acids, which are components of proteins and enzymes, sugars - part of the "backbone" of DNA and RNA, and fatty acids - structural components of cell membranes, adds BTA.

"Current results cannot directly elucidate the origin of life on Earth. However, I believe that they can improve our understanding of the reserves of organic molecules on early Earth before life began," said Yasuhiro Oba.