50mn tonnes of sugar from deep space delivered a sweet start to life on Earth

Scientists have detected sugar molecules at the centre of the Milky Way, suggesting that the clouds of interstellar gas could have carried a vital ingredient for life to bloom on Earth. Erythrulose – the first true sugar ever found in interstellar space - has been found at the galactic centre. Cosmochemist Izaskun Jiménez-Serra of the Spanish Astrobiology Center, led a team of researchers who believe that "interstellar erythrulose could have contributed to the sugar inventory available for early metabolic and replication processes" on our planet.

This happened about four billion years ago when our solar system was still taking shape. Up to 50 million tonnes of sugar fell on Earth from deep space, providing the building blocks of life. Sugars are molecules cells need for energy and as raw materials to build larger biological molecules. They also form the backbone of RNA and DNA. The interstellar clouds could have similarly seeded other parts of the universe with life, the study suggests.

Earth's violent period of formation brought sugar for life

For nearly 300 million years, every planet in the solar system was bombarded with asteroids and meteorites. This is how we got our Moon. This is also when interstellar dust brought sugar to Earth. Simple sugar precursors such as glycolaldehyde and (Z)-1,2-ethenediol have been found in space before. However, scientists peered at the centre of the Milky Way to find true sugar, containing three or more carbon atoms. This region is filled with thick clouds of gas and dust that are rich with complex organic molecules.

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Two radio telescopes in Spain watched the cloud named G+0.693, where prebiotic molecules have been found. The team was expecting to find simpler sugars containing three carbon atoms. However, they were surprised to come across four-carbon erythrulose, which was at least 8 to 17 times more abundant than the three-carbon sugars. The huge amount of sugar at the galactic centre meant that Earth also got a lot of it in its initial years.

How much sugar fell on Earth?

“Based on the abundance of erythrulose measured in the molecular cloud, the researchers estimate that between 0.5 and 50 million tonnes of this sugar could have reached Earth’s surface during the late heavy bombardment,” the team said.

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They also used the data to understand how sugar forms in interstellar space. Analysis showed that it formed on the icy surfaces of tiny dust grains carrying two-carbon molecules – glycolaldehyde and ethylene glycol. When activated by radiation, they could combine to build erythrulose. The discovery shows that complex molecules “can form under interstellar conditions”.

“The detection of erythrulose is very exciting because it opens up the possibility of discovering in space other sugars such as ribose, which is part of RNA, and other important molecules for the origin of life,” co-author Carlos Briones said. They concluded that as the sugars were knocked off the cosmic dust, they could have landed not only on ancient Earth but also somewhere else in the universe.