Based on many years of data and observations, scientists approximate the Earth to be around 4.5 billion years old. The earliest evidence of life that has been found exists in Greenland, and consists of fossilized remains of cyanobacteria, otherwise known as stromatolites. These fossils date back to 3.7 billion years ago, and even still, scientists believe that life may have gone back even further, due to rocks in Australia that contain high levels of carbon--an element that is majorly involved in most biological processes. This evidence raises the question of how life actually formed all those years back, and many different scientists propose different theories. Some of these include life coming from outer space, finding its way to Earth by means of an asteroid or comet. Others believe that there are several origins of life, and that life formed on Earth through a series of chemical reactions. These reactions are hypothesized to have led to the creation of self-sufficient systems that formed organisms. Whether one theory is correct or not, scientists still do not know for sure. However, by looking at the existing evidence, such as the cyanobacteria that is still around today, and by examining RNA and DNA qualities, they have a better idea of what very well might have been.
Scientists have widely accepted the idea that the primary molecule for life was RNA, a molecule made up of nucleotides that aids in protein synthesis and works as an on/off switch for many genes. However, upon the emergence of DNA, RNA was replaced due to the more stable and better performing nature of DNA. Since DNA is the basis of all life in organisms today, we can study it and gain multitudes of knowledge from studying its structure and functions. Perhaps we will never know the exact origins of life on Earth, but by continuing research on these molecules that we know have been around since the start, there is a much better chance at getting there. I think that the fact that we do not know the exact origin of life on Earth is very interesting because there are so many different explanations that can account for it. However, the fact that we know that RNA was the primary molecule is a step in the right direction because we have a lot of knowledge about it, and continue to study it nowadays. Perhaps one day we will make a discovery that answers how exactly life began on Earth, but until then we can only wonder.