Rigveda is not a scientific evidence and is widely believed to have been dated 500 BC. For simple reason that Indian script did not exist before that, it can not predate IVC which has an older script.
Dating of sand grains from dry bed of Saraswati was carried out in 2014 and compared to Yamuna river. Results indicate that Yamuna river stopped feeding it some 10,000 years ago this making it a seasonal river before IVC. Saraswati does not originate from high glacial mountains hence can not maintain year round flow. Only way to maintain year round flow is being fed from Yamuna river which changed course some 10,000 years ago making Saraswati seasonal during monsoon only. IVC settlements are found along Saraswati but no major city as big as Harrappa or Mohen Jo Daro. Big cities need year round flow to sustain.
Persian civilization had not appeared at the time of IVC. Persian civilization is contemporary to Greek civilization much later.
Without disrespecting a religious scripture, I have to say that ancient stories (which may well be untrue) get exaggerated over time especially when you attach religion to them. One can believe them in religious sense but they hold no weight in scientific context unless proven with hard evidence. There is no evidence of great armies at the time of IVC which was as the evidence suggests very peaceful civilization. They were more into trade, economy and welfare of citizens than warfare and religion. Very few weapons have been found at IVC sites and illustrations on IVC artifacts do not show any scenes of war or conflict. There is no violence, weaponry or religious rituals on IVC artifacts in sharp contrast to Hindu religious artifacts of early era.
Again science asks for proof. If anyone was in iron age then iron tools would be found dated to that period. Just like iron told were found at Mehr Garh site belonging to late Mehr Garh period but at the same site early periods only give you bronze tools. Evidence not our nationalism or religious bias is the way to deal with subject.
Obviously humans mix up. Evidence suggests that purest of IVC genes maybe with people of interior Sindh and central Punjab all along river Indus and its feeding rivers. Just three days back IVC site has been discovered at Dera Ismael Khan in KPK.
For truth please refer to works of universities and not biased websites and newspapers. History is just as is. And at the moment it tells us that human race spread out from Africa. It also tells us that when IVC was at its peak, India as it stands today was thickly forested and did not even had a script. None of the Vedas were there (how could they as written script was yet to be developed).
As far your claim of 20,000 years old cities under water cities, Indians the oldest civilization and origin of human race, I really can not answer to such claims. Nobody can. It is likely religious beliefs. Science has no space in it. By the way there is no such scientific evidence as you claimed. Coastline extended not receded and hence cities would not go under sea they would rather move away from coastline. IVC coastal towns and trading posts in Balochistan are much further away inland now. Please do not make outrageous claims.
Please learn to differentiate between a settlement, a town, a city state and a civilization. People who erected stone henge in England do not qualify as civilization. Earliest human city found outside Africa is Mehr Garh, Pakistan. For anything of this skill and complexity anywhere else, you need experts to let work there and use scientific techniques to ascertain anything. A masala news is for those who aren't open to truth.