Age of the earth according to Vedic chronology
According to Vedic chronology, Hinduism describes the age of the earth in detail. Details can be found in the Bhagwat Maha Purana or Bhagwatam.
Our earth is part of a material manifestation called a brahmanda, a group of interrelated but separate regions or abodes called lokas, each conditioned by its respective quality of material time and space. In other words, what would be equivalent to one year in one of these lokas may be correspond to 12,000 of our earth years.
Most of our brahmandais subtle and imperceptible to us. Our earth planet is part of this configuration. A brahmanda is basically comprised of one planetary system with an earth inhabited by living beings, a sun and the above described regions.
According to the chronology of Hinduism, the divine personality who creates this with God's grace and who oversees it is called "Brahma" (the creator). This is a seat or position located in the subtle or celestial regions of a brahmanda (Brahma - name of the creator), anda - his spherical creation, literally 'egg'.)
In one galaxy, there is an inestimable number of brahmandas (earth planet + other interrelated and subtle abodes) and their corresponding Brahmas.
The supreme creator or original inspiration for the creation of the entire universe is God.
How old is the earth? The earth came into existence with Brahma and will exist as long as he does. As long as Brahma lives, his creation continues to exist. When his term ends, this brahamanda will enter into absolute dissolution.
In between, there are periodic episodes of dissolution and creation of a lesser order, in which the earth enters a period of dormancy, when all life ends, but is again restored. Brahma is the personality that observes and maintains this schedule.
A soul incarnates in a particular brahmanda and remains there until its end. After this, that soul will enter another brahmanda. This has happened eternally for all the souls and will continue eternally. Only the soul who becomes liberated from maya is exempted from this.
We can calculate the age of the earth from the age of Brahma. The Vedic chronology of Hinduism uses a base unit of calculation called a chaturyugi. This is comprised of 4 yugas (periods of time). Their lengths and corresponding names are:
1,728,000 years = sat yuga
1,296,000 = treta yuga
864,000 = dwapar yuga
432,000 = kali yuga
4,320,000 years = one charturyugi (one 4-yuga cycle)
1000 chaturyugis = one day of Brahma
1000 chaturyugis = one night of Brahma
8,640,000,000 years = one full day (24 hours) of Brahma
100 celestial years = age that Brahma lives to
50 celestial years = Brahma's current age, or,
155.5 trillion years = the current age of this earth