How can life emerge from an environment with no life? is a puzzling question. About 3,6 billion years ago, one billion years after the formation of Earth, the first simple cells (prokaryotes) appeared on our planet. Many experiments were made to explain the first steps of the beginnings of life on Earth, and some of them showed that, given the good conditions, self-replicating molecules and simple cells could emerge from the oceans at that time.
The conditions at the surface of the Earth around 3,6 billion years ago were very different from what they are today. They may have been very close to what happens nowadays in the modern hydrothermal vents: vapour-dominated zones, very rich in minerals, where life can develop without any oxygen.
There are many different theories on the apparition of life on Earth, and this intriguing problem is not totally solved yet.