Earth is estimated to be about 4.5 billion years old, hand for much of that history, it has been home to life in one form or another. Today, there are several theories for how life arose on Earth. The first of these is that life was created by a Supreme Being or spiritual force. The second theory is that life began in another part of the Universe, and arrived on Earth by accident when a comet or meteor crashed.
Scientists say that life began around 3.5 billion years ago as a result of a complex sequence of chemical reactions that took place spontaneously in the Earth’s atmosphere. Molecules were formed as a result of these reactions. The molecules then interacted with one another, and this eventually led to the earliest forms of life.
The first beings were probably bacteria which survived on naturally occurring food, and did not breathe oxygen. The fossils of these oldest forms of life have been found in Australian rocks dating back 3.5 billion years.