Disclaimer: There is no definitive answer to this question. This article is our perception based on our research on work done by various scientists.
When we look around at the world today, it is easy to be awestruck by the incredible variety and extravagance of life on this planet. From the tiniest microbial organisms and the largest carnivores prowling the wild to dense jungles and rich coral reefs, life is abundant and beautiful in almost every corner of Earth.
One of the best things about humanity is our ability to self-analyze and reflect on existence; when we do that, one of the most obvious questions is…. how did life begin?
Were we dropped onto this planet by some supernatural deity, who also populated it with the millions of different species we know today? Did “life” arise from an alien species using our planet as a terrarium? Or is there a slightly more scientific explanation for life on Earth?
The Building Blocks of Life
To figure out how life began, we need to take a journey back more than 3 billion years, far before the rise of humans, dinosaurs, land animals, and even multicellular organisms. In other words, we want to go back to the “primordial soup” stage of our planet, when things were still very messy!
The Earth itself formed about 4.6 billion years ago, and it took roughly a billion years before things calmed down enough for life to even have a chance. Temperatures were higher and conditions were brutal – definitely not a place humans could have survived. The planet consisted of an atmosphere primarily composed of ammonia, methane, and hydrogen. This highly concentrated atmosphere was exposed to many different energy sources in those volatile early days of our planet, such as radiation from the formation of the solar system and energetic releases of our planet as it solidified and formed its core.
Eventually, the (atmosphere + energy) began producing monomers, which are basic organic molecules that contain carbon. These basic molecules accumulated into the famous “chemical soup” that we hear about so often, but this is where things get quite confusing…
The basic building blocks of life (as we know it now) are amino acids, RNA and DNA. These three substances can be found in every single “living thing” on our planet, so it stands to reason that one of those things started the whole process of life. However, going from a chemical soup of simple carbon compounds to amino acids, proteins, and DNA (as well as bonsai trees and kangaroos) is a BIG jump.
The Mysterious Grey Area…
RNA ends up being the most important character in most modern theories about how life arose. Essentially, RNA is DNA’s lesser-known cousin, but is responsible for the creation of proteins. The idea is that RNA was one of the simple monomers formed in the soup, and it began to self-replicate. Eventually, it began creating simple proteins (similar to what RNA does now). Those proteins eventually transformed or represented the first simple cell.
However, there is still a lot of uncertainty about that idea, namely how RNA “knew” how to behave, or whether they were actually responsible for proteins… perhaps it was the other way around? Proteins could have formed in that soup and retroactively created a mechanism for their reproduction, namely RNA. Again, these are the earliest moments of life, so the complexity of the discussion does get a bit “heady”.
Finally, amino acids need to be considered; they could have also been the catalyst for the creation of RNA and proteins after forming naturally in the primordial soup.
Finding the Answers
By combining simple chemical compounds with ultraviolet light in a laboratory, subunits of RNA have been artificially created, which has made the RNA origin story a very popular theory. It seems the most likely, and a large number of scientists and research endeavors operate on that idea, but no one actually knows! There are still questions to answer about the jump from protein creation to cellular “life”…
Furthermore, some recent research has pointed towards a protein-based world, rather than the more popular RNA world theory, raising even more questions about our earliest “living” ancestor.
What we do know is that whatever this mysterious ancestor is, it is the fundamental thing that connects every living thing on Earth, proving that we truly are all connected. Affectionately referred to as LUCA (Last Universal Common Ancestor), determining the identity and function of LUCA will be very valuable.
Attempts have been made to simulate those early Earth conditions in a laboratory, and amino acids were stimulated with temperature and energy, and their reactions were monitored. It was found that those amino acids did have the basic ability to undergo protein folding, meaning that it’s a viable explanation for life’s rise on this planet.
How About Some “Comet” Relief?
While there are plenty of theories about what happened on our planet that led to the development of life, many researchers choose to turn their eyes outward. Earth has been bombarded by countless meteors, asteroids, and comets over its more than 3-billion-year history, and some theorists believe that life arose as a result of a cosmic collision.
Icy comets contain a wide array of materials, including water, ammonia, methanol, and carbon dioxide in frozen states. When one of these massive comets entered Earth’s atmosphere, it could have contributed trillions of pounds of organic matter, arguably far more than what existed on the planet before these icy bombardments. The energy of impact, combined with these basic organic molecules, could have contributed to the rise of life. Sudden intense pressures and temperatures could have stimulated organic synthesis, although we have yet to replicate these events in laboratory settings.
This theory is closely related to the proposal that all the liquid water on earth arose from this sort of icy comet bombardment (a convenient tie-in…. two birds with one stone, so to speak), there are plenty of critics. Many argue that the levels of deuterium (a molecule present in the “heavy water” of comets) is far greater than deuterium levels found in the water found on Earth.
The debate rages on, and the research continues, but more theories are always better than less, right?
What About Aliens?
One of the less scientifically acknowledged theories includes the rise of life on this planet being connected to aliens. Now, this isn’t to say that little green men came down and grew us, or evolved into us…. think smaller. Imagine if microbial life from some other planet, perhaps, came soaring into our atmosphere on a meteor. Maybe that planet had been destroyed by an asteroid impact, and some of its “life” was flying through outer space.
That microbial life from an “alien” source could have interacted with the materials present in our primordial soup (simple monomers) and given rise to life on Earth. While this is slightly farfetched in the eyes of many people, without a definite explanation, and some serious grey areas in our knowledge, many theories are entertained in scientific and research circles (and by conspiracy theory lovers!).
So, in answer to the question, “How did life on Earth begin?”, there isn’t one clear answer, but the pursuit of that answer continues to drive research and discussion around the globe!