Unveiling the Origins of Life: Support for the 'RNA World' Theory
The fundamental building blocks of life, including the crucial molecule RNA, might be prevalent across the cosmos. New scientific experiments suggest that the formation of RNA on Earth could have been a simple process roughly 4.3 billion years ago.
RNA, or ribonucleic acid, is a less complex relative of DNA. DNA holds our cellular biology's genetic information. RNA, however, has multiple forms. Messenger RNA (mRNA) is created from DNA and carries instructions for protein formation. Ribosomal RNA (rRNA) forms ribosomes which are essential for protein production. Finally, transfer RNA (tRNA) synthesizes proteins from mRNA.
The 'RNA World' Hypothesis
Due to its simplicity compared to DNA, RNA is believed to have been formed first. Given its capacity to carry genetic information and generate other molecules, RNA is often considered the key player in life's origin on Earth. This theory is commonly referred to as the 'RNA world' hypothesis. Under this theory, the earliest single-celled organisms would have used RNA instead of DNA for replication and copying their genetic information.
However, understanding how RNA came into existence has been a complex task. What prompted the ingredients of RNA to combine in a specific manner and undergo the right sequence of chemical reactions? The chances of RNA forming purely by coincidence seem extremely low.
Therefore, scientists search for ways that could inevitably lead to the formation of molecules similar to RNA. A popular method is the six-step Discontinuous Synthesis Model (DSM).
The Role of Borate in RNA Formation
A significant hurdle in this method is borate, a group of common compounds found in seawater. Borates are oxyanions, which are atoms or molecules with a net negative electrical charge. Moreover, borates contain atoms of both boron and oxygen. There was a belief that borates obstruct some of the reactions on the chemical pathway leading to RNA.
Contrary to this belief, a recent study by a group of biochemists suggests that borates are actually beneficial for the formation of RNA.
The researchers conducted experiments in which they mixed the ingredients of RNA, namely the five-carbon sugar ribose, phosphates, and the four nucleobases used by RNA, in a solution that also contained borates and basalt. They then heated the mixture and let it dry out, replicating conditions they believe were common around underground aquifers on early Earth.
The results were intriguing. RNA had formed in the mixture. Furthermore, instead of hindering the process, the borates supported some of the steps in the DSM model, such as stabilizing the ribose molecules that can often be unstable and break down, and assisting in the production of phosphates.
Relevance to the Cosmos
Supporting these findings, recent discoveries from material brought to Earth from an asteroid reveal the presence of ribose, meaning all the ingredients of RNA have been identified in the collected samples.
The study suggests that a large celestial body, similar in size to a known asteroid and filled with RNA's ingredients, could have brought the building blocks of RNA to our planet. They estimate this event and the consequent production of RNA took place 4.3 billion years ago, around 200 million years after Earth's formation and 200 million years before the oldest evidence for life on Earth yet discovered.
Until now, RNA had only been formed in laboratories through deliberate triggering of chemical reactions by humans. The researchers argue this is the first instance of RNA being produced in a lab without direct human intervention, though some critics argue that even the act of assembling all the building blocks of RNA in a test tube is a form of human intervention.
Moreover, it's worth noting large asteroid impacts also occurred in the early days of Mars' history, which means RNA's building blocks could have been delivered to the Red Planet as well. Interestingly, borates have also been found on Mars, suggesting the necessary conditions for RNA production could have existed there too.
While RNA is not life itself, it is crucial to almost all known forms of life. If RNA formed quickly on Earth, in geological terms, it could have provided a shortcut to the emergence of the first simple organisms on our planet.