I've been doing a little research (not extensive yet, by any means) into exactly how old atheism and how it came into being.
In my explorations, I came across descriptions of the Carvaka philosophy.
Carvaka is a philosophy that's very ancient, Indian in origin, atheist, (lacks a belief in Gods), and secular humanist in nature.
A general description:
The system of philosophy named after its founder, Carvaka, was set out in the Brhaspati Sutra in India probably about 600 BCE. This text has not survived and, like similar philosophies in Greece, much of what we know of it comes from polemics against it and remarks by its critics. There is a further similarity with Greece in that this is a rationalistic and skeptical philosophy, thus undermining the widespread belief in the West that Indian philosophy is primarily religious and mystical. Amartya Sen has argued, in fact, that there is a larger volume of atheistic and agnostic writings in Pali and Sanskrit than in any other classical tradition�Greek, Latin, Hebrew, or Arabic. He adds that this applies also to Buddhism, the only agnostic world religion ever to emerge.
Carvaka's philosophy developed at a time when religious dogma concerning our knowledge of reality, the constitution of the world, and the concept of an afterlife were being increasingly questioned, both in India and elsewhere. Specifically, the school of Carvaka contained within itself a materialism that ruled out the supernatural (lokayata), naturalism (all phenomena described in terms of the properties of the four elements), rejection of the Vedas (nastika), and a skepticism that included rejection of inferential logic, or induction.
Source: Humanist Texts
In addition, Carvaka was opposed to the Caste system and Brahminism.
The following sums it up:
Fire is hot, water cold,
refreshingly cool is the breeze of morning;
By whom came this variety?
They were born of their own nature.
This also has been said by Brhaspati:
There is no heaven, no final liberation,
nor any soul in another world,
Nor do the actions of the four castes,
orders, or priesthoods produce any real effect.
If a beast slain as an offering to the dead
will itself go to heaven,
why does the sacrificer not straightway offer his father?
If offerings to the dead produce gratification
to those who have reached the land of the dead,
why the need to set out provisions
for travelers starting on this journey?
If our offering sacrifices here gratify beings in heaven,
why not make food offerings down below
to gratify those standing on housetops?
While life remains, let a man live happily,
let him feed on butter though he runs in debt;
When once the body becomes ashes,
how can it ever return again?
If he who departs from the body goes to another world,
why does he not come back again,
restless for love of his kinfolk?
It is only as a means of livelihood
that brahmins have established here
abundant ceremonies for the dead -
there is no other fruit anywhere.
Hence for kindness to the mass of living beings
we must fly for refuge in the doctrine of Carvaka.
Source: Daylight Atheism
If you take each verse and extract it's fairly clear cut meaning. The resemblance to current secular humanist approaches is remarkable.
Amartya Sen, an Indian atheist and Nobel Prize winner, writes about Indian Atheism in his book, The Argumentative Indian.
He also indicates that Indian Atheism goes back to approximately 1500 BC. (I'll be buying his book to get further details).
Interview with Amartya Sen.
Some theists, for reasons known only to themselves, are currently pushing three fallacious claims:
1. atheism came into being as a reaction to Christianity.
2. atheism means godless.
3. atheism is a religion.
Of course, all of these claims are false, and I can only assume that they provide the foundation for some anti-atheist argument which they wish to present.
The existence of Indian atheism proves that atheism didn't come into existence as a reaction to Christianity because it predates Christianity. Atheism is the reasonable default position.
The last two are easily disputed by looking up both the term atheism and the term religion in any dictionary and realizing that a lack of belief in god(s) doesn't constitute a religion (a set of beliefs).
Atheism, lack of belief in god(s) has existed for thousands of years because for thousands of years there have been people who believe in reason, science, humanistic principles and not superstition.
Written by Trance Gemini of AvC