If you ask a room full of biologists how life arose on our planet, you could start a fistfight. Current theories clash on details such as which came first: genes or protein, where life may have first formed and even whether it originated here or was deposited on our planet by a comet or asteroid.

The classical problem with origin theories is that, with the cells that currently litter our planet, there is a complex interrelationship between proteins and genes. Proteins need genes to be built, and genes require proteins to replicate. Without one, the other can’t exist. Furthermore, the chances of both arising at the same time, perfectly suited to the other’s replication, are slim to none.

So one had to have come first and had to have a mechanism in place for it’s own reproduction. Depending on which polymer you believe came first, protein or genes, you would either support the “protein first” theory, or the “genes first” theory.

Genes first

In the genes first theory, genetic material — namely ribonucleic acid (RNA), the single stranded cousin of DNA — constituted the first self-replicating molecules. In your cells, RNA acts like a go-between, conveying the information stored in your DNA to organelles called ribosomes that translate RNA’s code and make proteins. At first glance it seems odd that researchers could suggest that RNA could have been the first self-replicating molecule on our planet. But RNA has a dirty little secret.

RNA, like proteins, can fold into complex shapes, and form enzymes, or molecules that catalyze the formation of other molecules. Called “ribozymes,” these RNA-based enzymes have been found in plant viruses and even in the ribosomes in our own cells.

The RNA world hypothesis states that, through random chance, RNA nucleotides formed into a self-replicating ribozyme that eventually became more and more complex and sophisticated. This was just a theory though, until 2008 when researchers working at the Scripps Research Institute in California announced that, through a process known as “in vitro evolution,” they had created an RNA molecule capable of performing “efficient perpetual self replication.”
This discovery lent credence to the RNA world hypothesis.

Protein first

Amino acids — the basic molecules that combine in long chains to form proteins — can be spontaneously created. This was first demonstrated by the “Miller-Uray spark flask experiment,” which combined water and gasses, thought to be present on a primordial Earth, and exposed them to electric sparks simulating lightning. When the contents of the flask in which the experiment took place were investigated, Miller and his team discovered that several amino acids had formed.

The protein first theory states that some of these amino acids formed into proteins, which, by random chance, eventually combined into complex proteins that could perform simple metabolic tasks. These metabolic tasks eventually increased in complexity until the proteins became self-replicating, forming the basis for life on earth.

Panspermia

Panspermia is the theory that life did not arise on this planet, but originated elsewhere and was deposited here. The theory postulates that life may have hitched a ride on an asteroid, or perhaps, according to the theory of “directed panspermia” as championed by Francis Crick — who is also the co-discoverer of DNA — intentionally by an intelligent alien species.

While there is no direct evidence to suggest that panspermia, let alone directed panspermia, ever took place, advocates point to several pieces of circumstantial evidence, such as the fact that amino acids have been detected in space, both in clouds and on objects such as comets and meteorites, which travel throughout the cosmos.

Another piece of evidence is the discovery of several species of bacteria that have very strange adaptations, which would make them ideal candidates to make the journey between worlds. One such bacterium, Deinococcus radiodurans, can withstand 2,000 times the radiation of any human making them ideal candidates to survive an interstellar journey to “seed” another planet.

There is the possibility that we may never know the true origin of life on this planet, but this is not a bad thing. If we truly knew the origin of life there would be a lot less interesting debate on the subject and a host of bitter scientists who backed the wrong side.