Could life on Earth have been brought here from asteroids?

Perhaps many people have thought about this question: Where does life come from?

When the Earth was born more than 4 billion years ago, it was still a hot ball of fire, with volcanic eruptions, lightning and thunder, and a very harsh environment. How could life evolve in such a place? In 1953, the famous Miller experiment proved that the primitive Earth environment had the conditions to produce organic matter. When he used a flask to simulate the primitive atmospheric conditions and supplemented it with electric sparks, amino acids, the basic units of life, appeared.

This is the most mainstream and oldest hypothesis about the origin of life. However, many recent research results have proposed another possibility - life may be an alien.

On February 26, 2023, a Japanese research institute released a related news: their probe "Hayabusa 2" brought back some samples from the asteroid "Ryugu". After analysis, it was found that the samples contained about 20,000 kinds of organic molecules composed of elements such as carbon, hydrogen, oxygen, nitrogen, and sulfur. Some of them are even amino acid molecules that are indispensable to life, such as alanine, which constitutes the protein of life on Earth.

What does this mean?

There is a theory that this means that life on Earth may have come from asteroids. These basic units of life may have been attached to meteorites and fell to Earth. After a long period of time, they have evolved into you, me, and all living things.

But some people also believe that the existence of organic molecules in such harsh environments as asteroids means that these organic molecules that constitute life are more likely to be born on Earth, because the environment on Earth is more suitable and milder. Moreover, looking at the vast universe, the Earth is not a very special planet. On the contrary, there are many planets with similar conditions to the Earth. Astronomers estimate that there are hundreds of millions of Earth-like planets in the Milky Way alone. From this perspective, it is very likely that life similar to ours will appear on other planets in the universe. In other words, humans are not alone in the universe.

There is another very interesting thing in the discovery of Hayabusa 2: half of the amino acid molecules from Ryugu are left-handed and half are right-handed, while the amino acid molecules that make up life on Earth are all left-handed.

What does this mean? Let me first explain to you what left-handed and right-handed are.

If the chemical composition of two amino acid molecules is exactly the same, but their three-dimensional structures are different and mirror-symmetrical, we call one of them left-handed and the other right-handed. This is a bit like our hands, both have five fingers that look exactly the same, but the two hands cannot be overlapped up and down because they are mirror-symmetrical.

Half of the amino acid molecules from "Ryugu" are left-handed and half are right-handed, which may mean that in an environment undisturbed by life, left-handed molecules and right-handed molecules should each account for half.

So why are all the life forms on Earth made up of left-handed amino acids? We don't have a definite answer. This could be a random event. When life was formed, there were left-handed and right-handed amino acids on Earth, but life on Earth was randomly born from left-handed amino acids. It is also possible that in the early days of life, left-handed amino acids had some survival advantage over right-handed amino acids, thus eliminating life forms made up of right-handed amino acids.

In any case, there is no definitive conclusion on the origin of life. The discovery of Dragon Palace did not bring decisive evidence, but added more clues. Only when we collect enough pieces can the puzzle of the origin of life show its true appearance.

This article is a work supported by Science Popularization China Starry Sky Project

Team/Author Name: Duan Yulong

Review: Tao Ning

Produced by: China Association for Science and Technology Department of Science Popularization

Producer: China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.