Scientists from the University of Zurich and the Max Planck Institute for Molecular Genetics, as well as the Icahn School of Medicine at Mount Sinai have come together to summarize recent evidence has challenged our working theory on the origin of life. Previously, scientists thought early life may have arisen from proteins or other chemical reactions important for life reacting in the hot soup of early Earth before there were actually cells. Then, it has been thought that these chemical reactions may have later been taken over by early cells.
However, long ago, after discovering large amounts of amino acids, DNA, and RNA on meteorites in our cosmic neighborhood, researchers again had to shift their train of thought. This paper explained that experiments that mimicked the temperature, acidity, pressure, and energy of an Early earth provided evidence that life may have come from random assortments of RNA and other small molecules. Then, the authors continued, a hypothesis was developed that RNA may have been the primordial “first lifeform” which took shape on our planet and may have already formed on others. The authors claim that this led to this most recent and widely accepted theory: our world may have been a “RNA world” at one point in its development; one in which life was composed of a few self-reproducing RNA molecules that worked to spread information as rapidly as possible and combined with amino acids to make proteins which could assist it. The problem with this idea is that researchers are still struggling to engineer RNA molecules that create themselves; a necessary condition if RNA is to reproduce and be able to evolve. Enter the viroid – viroids are, essentially, a piece of RNA that can copy itself. Viroids can also insert themselves into a host’s DNA using normal cell processes.
A study highlighted in this article attempted to imitate RNA. Researchers showed that, in solutions of rich in salts and sugars, RNA can spontaneously regrow quite rapidly. These molecules were able to reproduce across 74 generations. From looking at how the sequences changed over these generations, it was determined that viroids replicated fast and continually became smaller and smaller strands of RNA.
The authors conclude that, given what we know about viroids, the idea of a “viroid-first” origin-of-life theory should be seriously considered, though there is not yet enough evidence to be confident. The good news is that detecting small organic molecules and viroid particles in the depths of space and below the surface of other planets is a lot easier to do than finding evidence to support other origin of life theories, since this theory uses techniques and science that are already familiar to biologists. Genetic engineers are still struggling to create self-copying RNA outside of a viroid-like model and proteins and metabolic chemicals haven’t turned up in our observations of the space beyond our solar system.
Evidence of organic molecules such as pieces of RNA, DNA, and proteins have been found on recent meteorites. This demonstrates that space already has the conditions to allow for these chemical reactions to take place beyond Earth. The authors suggest that the beginning of life must have been simple, and the search for signatures of viruses, viroids, and small RNA and the modeling of these “life forms” may be where we need to turn our attention next to answer the questions about life in our Universe.