''The RNA world hypothesis suggests that life on Earth began with a simple RNA molecule that could copy itself without help from other molecules.''
''RNA can do far more. It can drive chemical reactions, like proteins, and carries genetic information, like DNA. And because RNA can do both these jobs, most scientists think life as we know it began in an RNA world, without DNA and proteins.''
The first RNAs
''So how did RNA evolve on Earth? Scientists think RNA building blocks (nucleotides) emerged in a chaotic soup of molecules on early Earth. These nucleotides bonded together to make the first RNAs. No sooner were they made than they broke down; however, new ones were made in their place. Some RNAs turned out to be more stable than others. These RNA strands grew longer and bonded nucleotides more quickly. Eventually, RNA strands grew faster than they broke down. This was RNA’s chance to start life.''
RNA offspring
''All living things reproduce. They copy their genetic information and pass it onto their offspring. And for RNAs to start life, they needed to reproduce too. This is why scientists think that the RNA world took off when an RNA emerged that could make copies of itself. As it did, new self-copying RNAs emerged. Some were better at copying themselves than others. The RNAs competed against each other, and the most successful won out. Over millions of years, these RNAs multiplied and evolved to create an array of RNA machines. At some stage, DNA and proteins evolved. Proteins began to drive chemical reaction in cells, and DNA—which is more stable than RNA—took the job of storing genetic information.''
