DNA building blocks found in meteorites
A study may have finally discovered where life on Earth originated, tracing our existence back to a meteorite that landed here billions of years ago.
Experts have long debated how Earth, one of trillions of planets created in the universe’s 14 billion-year existence, managed to cultivate life.
One theory was that the core materials that make up DNA were transported to Earth from space via a meteorite around 3.5 billion years ago. During this period, Earth would have been peppered by meteorites and comets from a chaotic and formative solar system.
While this theory had much support in the scientific community, it had had one glaring weakness: only two of the four main components of DNA had been found in space rocks.
Now, state-of-the-art analysis of three meteorites has spotted evidence of all four, proving that the necessary jigsaw pieces for life are found in space.
‘‘[The DNA chemicals] could have been generated by photochemical reactions prevailing in the interstellar medium and later incorporated into asteroids during solar system formation,’’ the researchers write in their study, published in the journal Nature Communications.
‘‘A diversity of meteoritic nucleobases could serve as building blocks of DNA and RNA [ribonucleic acid] on the early Earth.’’
The study said the accumulation of these scarce molecules faced ‘‘substantial geochemical challenges’’ on a developing planet with an atmosphere possibly dominated by carbon dioxide and nitrogen.
DNA underpins all forms of life. Its double helix structure is formed by two strands of molecules connected along their length by ladder-like rungs made of two chemicals joined together.
There are four chemicals – adenine, thymine, cytosine and guanine – known as ‘‘bases’’, and their arrangement makes up an individual’s genome. The order of these four bases is unique in every person, and provides their genetic code.
Previously, scientists had found evidence of guanine and adenine in meteorites, but had never spotted their complementary partners.
A team of Japanese researchers, led by Hokkaido University, obtained two samples of the Murchison meteorite, which landed in Australia in 1969, and one sample from both the Murray and Tagish Lake meteorites, which landed in the United States in 1950 and in Canada in 2000, respectively.
They were ground into a fine powder and subjected to hypersensitive analysis capable of detecting molecules at the parts per trillion level. More than 30 chemicals were identified, including the vital adenine, guanine, cytosine and thymine.