We have a LOT of evidence. The vedas have been universally agreed to be written before 3500 BC, at least. They are much older according to Indian / Eastern researchers. The Vedas talk about a river Saraswati. This river has been proven with archeological & satellite evidence to have dried up in 1900 BC. That means the Vedas & the Vedic civilization are much older & from an era when the Saraswati river was flowing. There are even more evidences. Many celestial events described in the Vedas completely match celestial events mathematically & corroborate with each other, and they have been dated to be about 7000+ years ago.