A new analysis of fallen meteorites in the United States, Canada and Australia is bolstering the idea that, early in Earth’s history, these objects may have brought vital chemical ingredients to the planet for the emergence of life.
In these meteorites, scientists had previously detected three of the five chemical compounds needed to form DNA, the molecule that carries genetic instructions in living organisms, and RNA, the molecule crucial to controlling the actions of genes. Researchers announced Tuesday that they had identified the final two molecules after improving the way they analyzed meteorites.
Unlike what was done in previous works, the methods used this time were more sensitive and did not involve the use of strong acids or high-temperature liquid to extract the five components, known as nucleobases. The information is from astrochemist Yasuhiro Oba, from the Institute of Low Temperature Science at Hokkaido University in Japan, lead author of the study published in the specialized journal Nature Communications.
Nucleobases are nitrogen-containing compounds and are crucial in forming the characteristic double helix structure of DNA.
Confirmation of an extraterrestrial origin from a complete set of nucleobases found in DNA and RNA reinforces the theory that meteorites may have been an important source of organic compounds necessary for the emergence of the first living organisms on Earth, according to the astrobiologist and co-author. study author Danny Glavin of NASA’s Goddard Space Flight Center in Maryland.
Scientists are seeking a better understanding of the events on Earth that allowed various chemical compounds to come together in a warm, watery environment to form a living, reproducing microbe. The formation of DNA and RNA would have been a major milestone, because these molecules essentially contain the instructions for building and operating living organisms.
“There is still a lot to learn about the chemical steps that led to the origin of life on Earth – the first self-replicating system,” said Glavin. “This research undoubtedly adds to the list of chemical compounds that would be present in the prebiotic broth. [presente antes do surgimento da vida] beginning of Earth.”
The researchers examined material from three meteorites: one that fell in 1950 near the city of Murray, Kentucky, one that fell in 1969 near the city of Murchison, in the Australian state of Victoria, and one that fell in 2000 near the Lake Tagish, in the Canadian province of British Columbia.
The three meteorites are classified as carbonaceous chondrites, made of rocky material that would have formed early in the history of the solar system. They are rich in carbon; about 2% of the mass of the Murchison and Murray meteorites is made up of organic carbon, while the Lake Tagish meteorite contains 4% of organic carbon. Carbon is one of the primary building blocks of Earth’s organisms.
“The three meteorites contain a very complex mix of organic molecules, most of which have yet to be identified,” said Glavin.
The Earth was formed approximately 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 oldest known fossils are marine microbial specimens dating to about 3.5 billion years ago, although there is evidence of life in older fossils.
The two nucleobases that have now been discovered in meteorites, cytosine and thymine, may not have been detected in previous analyzes because they have 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 others, amino acids, protein components and enzymes were needed; sugars, which are part of the backbone of DNA and RNA; and fatty acids, which are structural components of all cell membranes.
“Current results may not directly elucidate the origin of life on Earth,” said Oba, “but I think they can increase our understanding of the inventory of organic molecules present on early Earth before life appeared.”
