How long has religion existed?
Since the beginning of human thought - hundreds of thousands of years ago. When the first humans ran in fear from a bolt of lightning; felt the horror of a mother and baby dying in childbirth; witnessed a mountain explode in a fountain of molten rock; saw a comet plough through the firmament; watched one friend survive an unlikely accident when others perished; noticed the changing of the seasons;wondered where we came from and where we are going - they asked for an explanation.
Gods, Godesses, demons, angels, spririts, ghosts and goblins have long been the standard answer. Every year, a new god is created. People find a new Holy Object to bow down to, begging for luck, healing, blessings or for a message to be passed to a dead relative. During your lifetime, how many people have claimed to be the incarnation of one god or another, and gathered a following of thousands of devout believers? I remember one such person. He was Puttabarti Saibaba. Also how many psychics are available to communicate with the spirit world on your behalf?
For as long as people have had questions, there have been holy men and women ready to provide answers. Priests, priestesses, druids, shamen, witches, witch-doctors, vicars, monks, mediums, spiritualists, nuns and a thousand others - all claiming to have some mysterious link to the Unseen World, all claiming to know the Unknowable Truth.
Since the beginnings of human thought, the supernatural has been given as an explanation of the natural. Before the development of microbiology and space telescopes, all these mystical notions seemed to be perfectly reasonable. People prayed for rain, and eventually it rained. People made sacrifices, and they survived another year. Appease the Gods and the earthquakes will stop. Do as the priest says, and the Sun will appear again from behind the moon. Believe strongly enough, and the child will recover.
For hundreds of thousands of years, people have thought this way. And they still do - old habits are hard to break.
But what about atheism?
How old is that? A few decades? A few centuries? Atheism came into being with the first life-forms in the universe. For billions of years, creatures have had no belief in deities. Trilobites, dinosaurs, stromatolites - all atheist by definition. Did God reveal himself to early lizards? To early primates, sponges or fish?
Before the advent of human thought, it was impossible for gods to exist. Surely, sabre-tooth tigers and triceratops witnessed the same things then that we blame on gods today. A mother would see one of her offspring snatched by a predator, whilst it's sibling lived on. A herd of now-extinct herbivores would be startled by a fireball streaking across the sky. All were beyond the comprehension of the non-human minds that experienced them.
The events that drive us to create religions today have been going on for thousands of millions of years.
All the witnesses to those events were atheists, but they had not the brains nor the language to create a God to explain them. Wildebeest do not build an altar before testing the waters of a crocodile-infested river. Zebra do not light candles around the skull of a lion, praying for deliverance from predation.
Only we Homo sapiens, in this last tiny fraction of the planets history, have had the wit and intelligence to realize that all of these things that have been happening for countless centuries without us are the result of a Divine Will. Only humans have decided that the course of these events may be altered by closing our eyes, pressing our hands together and focusing really hard at the sky. Only the human brain is capable of establishing a two-way connection with the spirits of long-dead animals (also human, coincidentally).
Before humans, all life was atheist. Thousands, possibly millions, of spirit-beings have been thought into existence, thanked or blamed for natural phenomena, and then forgotten. In a blink of geological time, all current gods, godesses and assorted spooks will be gone - probably to be replaced by even more exotic and unlikely creations to take the credit or blame for everything. And so the cycle will continue.
As long as there are intelligent beings who remain ignorant of the workings of the world, or are not satisfied with those workings and wish for something more, there will be theism. Gods by the truckload will be created, worshipped and then forgotten - assigned to the waste-bin of mythology.
All current religions will die out or evolve, to be replaced by new ones, and the followers of those will look back and laugh at the fact that we could have been so primitive in our worship of Shiva, Vishnu, Rama, Krishna, Yahovah, Jesus or Allah, while they bend their knees to the latest supernatural invention.
There always have been, and there always will be, atheists. From the first self-replicating molecules, to the last galaxy-crossing machine intelligences, there will be creatures that have no belief in "Spirits of the sky". Religions come and religions go, but atheism outlives all gods!