Complex sugars have been found in a pair of asteroids, and this discovery could help explain how life formed on the Earth soon after it cooled.
Ribose and other sugars formed in space have been discovered in asteroids by researchers from Tohoku University, Hokkaido University, JAMSTEC, and NASA Goddard Space Flight Center. The particular isotopes of these sugars were found to differ significantly from sugars formed on Earth, revealing their extraterrestrial origin.
Investigators believe these sugars formed billions of years ago, during the formation of the solar system. Later on, the sugars, locked in asteroids, fell to Earth, where they were recovered by scientists. Three asteroids were analyzed by the international team of researchers who found sugars present in two of the samples.
“Analysis of sugars in meteorites is so difficult. Over the past several years, we have investigated the techniques of sugar analysis in such samples and constructed our original method,” said Yoshihiro Furukawa of Tohoku University.
The Chemistry of Life
Amino acids, phosphates, and nucleobases, central compounds needed for the formation of life, have previously been seen in meteorites. Sugars have also been detected in asteroids, but only the simplest sugar, dihydroxy acetone (along with sugar acids and alcohols), have been seen in extraterrestrial samples prior to this study. However, none of those compounds is essential to the formation of life, at least on Earth.
It is possible that ribose and other bio-essential sugars may have developed on the early, pre-biotic Earth. However, no geological evidence exists for the formation of these critical molecules prior to the formation of life on our world, and it is unknown how much sugar may have formed during that time.
However, nearly 4.5 billion years ago, the Earth experienced an era of frequent collisions with asteroids, comets, and failed planets, during a time known as the heavy bombardment period. Geologists studying gemstones called zircons know the Earth possessed significant quantities of water four billion years ago.
Toward the end of that era, bodies colliding with the Earth brought complex carbon-based molecules, including simple sugars and even more complex molecules, including buckyballs (spheres containing dozens of carbon atoms). These objects may have also been responsible for the formation of the oceans on Earth in that period.
The sugars could have developed into primordial RNA, which may have, eventually, developed into the first lifeforms on the planet. Sometime between 3.9 and 3.8 billion years ago, life had taken hold on the Earth.
“Meteorites contain a number of organic compounds including components of proteins and nucleic acids… Meteorites were carriers of prebiotic organic molecules to the early Earth; thus, the detection of extraterrestrial sugars in meteorites implies the possibility that extraterrestrial sugars may have contributed to forming functional biopolymers like RNA,” researchers wrote in a journal article published in The Proceedings of the National Academy of Sciences of the United States of America (PNAS).
The team also carried out a simulation showing how sugars may have formed in the depths of space, in the presence of water and heat.
Sugars are essential for a wide range or biological processes in all terrestrial lifeforms. Ribose is one of the most essential of these chemicals, as it can form RNA capable of storing genetic information and driving other reactions essential to the formation of life.
A Show of Hands
Just as your hands are not identical, but rather mirror images of each other, chemicals can develop in two forms — left- or right-handed. This chiral characteristic is usually expected to be seen in half of any product produced in a chemical reaction.
However, in all lifeforms on Earth, ONLY the left-handed version of essential compounds can form life and drive the processes need for living beings to carry out biological functions. No one is sure why this is the case, although the chemicals in living beings are always left-handed.
“Just as your left hand and your right hand are mirror images of one another, identical and yet opposite, so, too, organic compounds can exist as mirror-image forms of one another all the way down at the molecular level. But although they may look the same, they don’t always behave the same.”
- Walter White, Breaking Bad — Season 1 Episode 2
Thalidomide was developed as an anticonvulsive drug in the 1950's by a West German pharmaceutical company. It was found to act as a mild sedative, and seemed to ease the symptoms of morning sickness. In an era when sedatives were becoming popular, the drug was released in Europe.
Although early testing showed the drug was safe, no testing was conducted on pregnant women. Within a few years, more than 10,000 babies were born with severe deformities to their limbs. Chemists soon discovered that while the left-handed form of the drug was safe, the right-handed version of the molecule was highly toxic to developing fetuses. It was banned in 1962.
Further research will be carried out by the research team as they look at the chirality of the sugars found in these asteroids, and try to determine if molecules like these may have provided terrestrial life with its dependence on life-handed chemicals.
On the most basic level, a special treat of a sugary snack may bring us back to the very dawn of life on Earth.
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