Rg Veda date

The Rg Veda is at the heart of the debate.

We all agree that it is the oldest of the vedas and its language is very
ancient and pretty close to iranian. Some parts of the Rg Veda might
even be relics from common indo-iranian poetry.

Now how old is it ?

- the Rg Veda (not the other three vedas) does not mention rice.
- Horses are quite proeminent animals in this text.
- the word Aya meaning metal probably means bronze but may (or may not)
also refer to Iron.

If the Rg Veda was composed in the Indus Valley earlier than 2000 BC
this leads to several problems.

- Wheat began to be cultivated in the Indus Valley around 7000-6500 BC
(I don't believe the claim made by Badrinaryan in 2006 that underwater
cities have been found in the Gulf of Cambay dating back to 11 000 BC
making India the oldest urban civilisation in the world)
- Rice around 5000 BC. ? no definite referance on this, but it was known
to the Harrapeans.
- The Harrapean "golden age" circa 2600 BC.
- 3000 BC begining of copper metallurgy
- 2400 BC beginning of Bronze metallurgy
- 1700 BC beginning of iron metallurgy (in Anatolia)
- there is no evidence that the scant equine remains (jawbones) found in
a few Indus civilisation levels correspond to the modern horse (E.
Caballus). Wild equidae have existed throughout asia. They are much more
probably the remains of donkeys or onegers. Anyway, the domestication of
the horse was first achieved in the southern urals around 3500 BC. The
first unequivocal remains of a domesticated horse (drawing chariots) go
back to ca. 2000 BC in the Eurasian Steppes. There is no representation
of a horse drawing a chariot in Harrapean culture. The drawings of
"spoked wheels" ? from the Indus Civiliation need to be closely
examined.

So

a) why does the Rg Veda if it really was the produce of the Harrapean
Civiliation ignore rice.
b) HoW could the Vedic population use horses earlier than 2000 BC ?
c) why does the pictorial evidence from 4000-2000 BC (the age the
non-migration scholars propose for the compoition of the Rg VEda) from
the Indus Valley ignore horses (although there are possibly two
representations of some kind of Equidae, we would expect an animal that
figure so proeminently in the Rg Veda to appear much more often).
d) if the Rg Veda was written in 4000BC how could they know copper. If
in 3000 BC how could they know bronze. As for Iron, there is currently
no way of knowing from the text.