Answer

In Jain cosmology, one Pūrva is traditionally taken as 70,56,00,00,00,00,00 years — about 70.56 trillion earth years. ( jainknowledge.com)

Explanation

It is an extremely vast time unit, used to describe spans far beyond ordinary human history. ( jainknowledge.com)

Takeaway

So, 1 Pūrva ≈ 70.56 trillion earth years. ( jainknowledge.com)