The origins of life on Earth are believed to have begun around 3.5 to 4 billion years ago. Scientists propose that simple organic molecules formed in the early oceans, possibly through processes like lightning or volcanic activity. These molecules eventually combined to create more complex structures, leading to the first simple cells. One popular theory, known as abiogenesis, suggests that life arose from non-living matter under specific conditions. Another idea, called panspermia, posits that life may have been brought to Earth by comets or meteorites. Both theories aim to explain how life could emerge from inanimate substances.