Context: In a new study, scientists have said the last universal common ancestor (LUCA) could have formed just 300 million years after the earth formed. The origin of life on the earth is one of the world's most enduring mysteries. There are a number of competing theories but all of them lack conclusive proof.

About LUCA

• LUCA stands for Last Universal Common Ancestor. It's the hypothetical single-celled organism from which all current life on Earth (bacteria, archaea, and eukarya) is believed to have descended.

• LUCA represents the root of the tree of life before it splits into the groups, recognized today: Bacteria, Archaea, and Eukarya.

• LUCA is estimated to have originated around 4.2 billion years ago, which is about 300 million years after Earth formed.

• Modern life evolved from LUCA from various different sources: the same amino acids used to build proteins in all cellular organisms, the shared energy currency (ATP), the presence of cellular machinery like the ribosome and others associated with making proteins from the information stored in DNA, and even the fact that all cellular life uses DNA itself as a way of storing information.

• Through genetic analysis and evolutionary modeling, researchers pinpointed LUCA’s existence to about 4.2 billion years ago, just 400 million years after the formation of Earth and our Solar System.

• LUCA is not too different from modern prokaryotes, and clearly possessed an early immune system.

• It's believed LUCA had a small genome of about 2.5 million bases encoding around 2,600 proteins. It may have also had genes for immunity, suggesting it had to defend against viruses

What is the molecular clock?

• The molecular clock is a technique used in evolutionary biology to estimate the time elapsed since two species diverged. It's based on the theory that genetic mutations accumulate at a relatively constant rate over time.