Jyotiṣa Śāstra

Bhagavad Gita and Jyotish – about Brahma’s Day

Chapter 8. अक्षरब्रह्मयोगः akṣara-brahma-yogaḥ Yoga of imperishable Brahman

सहस्रयुगपर्यन्तमहर्यद्ब्रह्मणो विदु: ।
रात्रिं युगसहस्रान्तां तेऽहोरात्रविदो जना: ॥ १७ ॥
sahasrayugaparyantam ahar yad brahmaṇo viduḥ |
rātriṁ yugasahasrāntāṁ te ’horātravido janāḥ ||17||

Translation: Brahmā’s daytime (ahar yad brahmaṇo) is lasting a thousand Yugas (sahasra-yuga-paryantam), [and also] night is limited by a thousand Yugas (rātriṁ yuga-sahasra-antāṁ). It is understood by those people (te janāḥ viduḥ) who are day-and-night knowers (aho-rātra-vido).

अव्यक्ताद्‍ व्यक्तय: सर्वा: प्रभवन्त्यहरागमे ।
रात्र्यागमे प्रलीयन्ते तत्रैवाव्यक्तसंज्ञके ॥ १८ ॥
avyaktād vyaktayaḥ sarvāḥ prabhavanty ahar-āgame |
rātryāgame pralīyante tatraivāvyakta-saṁjñake ||18||

Translation: As the Brahmā’s day dawns (ahar-āgame), all manifestations [of living beings] (vyaktayaḥ sarvāḥ) come forth (prabhavanty) from the unmanifest state (avyaktād). As the night falls (rātry-āgame), they become dissolved (pralīyante) into that which is called unmanifest state (tatra-eva-avyakta-saṁjñake).

Satya 1,728,000 years
Tretā 1,296,000 years
Dvāpara 864,000 years
Kali 432,000 years
Total (Mahāyuga) 4,320,000 years
x 1000
Brahmā’s daytime 4,320,000,000 years

Current Scientific view:
Age of Universe – 13,800,000,000 years
Age of Solar System – 4,600,000,000 years
Age of Earth – 4,567,000,000 years
The Rhyacian Period lasted from 2,300,000,000 to 2,050,000,000 years ago. At this time, the first multicellular life exists.
In 3,500,000,000 Life on the Earth should already disappear (since condition will be as on Venus).

So, we can see that scientific view – how long the life on the Earth should exist – roughly corresponds to the Day of Brahma.

Further, we can learn more about mass extinction events and manvantaras.

Bhagavad Gita