Scientists have found new evidence that the basic organic molecules necessary for the emergence of biological life on Earth came from space. Fossils on the planet show signs of cellular organic matter in layers dating back 3.7 billion years—almost immediately after the Earth cooled to a safe level. In this case, cellular life would not have had enough time to evolve from ordinary chemical elements. Simple organic molecules were needed, evidently from space.

Scientists have long detected complex organic molecules in interstellar space, particularly carbon and hydrogen compounds. Generally, these belong to a class called polycyclic aromatic hydrocarbons (PAHs), which are ring-shaped structures made of dozens of atoms. Interestingly, earlier theories did not account for the existence of molecules in interstellar space more complex than two-atom combinations. Science assumed that ionizing radiation, especially intense in star-forming regions, would consistently break down complex molecules. However, with the advent of radio astronomy, PAH molecules were detected everywhere, though one problem remained.

In the infrared and radio wavelengths, terrestrial science has learned to distinguish large PAH molecules. Meanwhile, the processes that give rise to biological life require simpler molecules. In particular, it would be desirable to detect, for example, pyrene—one of the smallest PAH molecules, made of only 26 atoms. Pyrene would struggle to survive in the dense ionizing radiation of young stars in star-forming regions, but it also cannot be detected in radio wavelengths. So scientists took a different approach.

It is known that in combination with cyanide, pyrene forms cyanopyrene (1-cyanopyrene, C17H9N). Cyanopyrene is easily detected by radio telescopes, and knowing the distribution and ratio of cyanide allows researchers to estimate the expected quantity of pyrene in the observed area of space.

Scientists examined the star-forming region closest to Earth—the Taurus Molecular Cloud, located 450 light-years away. The amount of pyrene calculated for this cloud of cold interstellar gas and dust exceeded all expectations. Despite the abundance of newborn stars in this region and the ongoing star formation, pyrene—one of the fundamental "building blocks" for the emergence of biological life—is plentiful here. This indicates that it will likely settle on future planets in significant quantities and was probably present in abundance in the cloud of dust and gas that eventually formed the Solar System.

Interestingly, pyrene was also detected in samples from the asteroid Ryugu, providing further evidence of its existence in cold interstellar clouds of matter. This new discovery has further strengthened the hypothesis of an extraterrestrial origin of life, at least at the level of basic organic molecules.