Originally posted by RBHILL
I thought it was 1000 years is like a day. So 1 billion years is 1 million days=2737 years about.
Get your calculator out and mull this over...
Kali-yuga (Iron Age)
Duration - 1,200 demigod years (1000 + 100 sandhya + 100 sandhyamsa)
or 432,000 human years
Life span - 100 years (or 50, SB 12.2.11)
Yuga-dharma - Chanting the Hare Krsna mahamantra (harinama sankirtana)
Yuga-avatara - golden or yellow but generally black. Lord Caitanya, who is Krsna Himself, appears only in the Kali-yuga immediately following the appearance of Sri Krsna in Dvapara-yuga.
Symptoms of Kali-yuga: "O learned one in the age of Kali, men have but short lives. They are quarrelsome, lazy, misguided, unlucky and above all, always disturbed." (SB 1.1.10)
The four yugas are known as a divya-yuga, or maha-yuga. One divya-yuga is 12,000 years of the demigods (4,320,000 human years). One thousand divya-yugas equals one day of Brahma (4,320,000,000 human years).
In each Brahma's day there are fourteen Manus (patriarchs of mankind). Each Manu enjoys a life of seventy-one divya-yugas or 852,000 years of the demigods (306,720,000 human years). After the dissolution of every Manu a new Manu comes.
With the change of Manu the universal management also changes. Each manvantara is preceded and followed by the yuga-sandhya in length of one Satya-yuga. The yuga-sandhyas are periods of partial devastation and creation.
Also
Each yuga cycle is composed of 4 yugas. The first, the Satya-yuga lasts 4800 years of the demigods. The second, the Treta-yuga, lasts 3600 years of the demigods. The third, the Dvapara-yuga, lasts 2400 years of the demigods. And the fourth, Kali-yuga, lasts 1200 years of the demigods (Bhagavata Purana 3.11.19). Since the demigod year is equivalent to 360 earth years (Bhaktivedanta Swami 1973, p. 102), the lengths of the yugas in earth years are, according to standard Vaishnava commentaries, 432,000 years for the Kali-yuga, 864,000 years for the Dvapara-yuga, 1,296,000 years for the Treta-yuga, and 1,728,000 years for the Satya-yuga. This gives a total of 4,320,000 years for the entire yuga cycle.
One thousand of such cycles, lasting 4,320,000,000 years, comprises one day of Brahma, the demigod who governs this universe. A day of Brahma is also called a kalpa. Each of Brahma's nights lasts a similar period of time. Life is only manifest on earth during the day of Brahma. With the onset of Brahma's night, the entire universe is devastated and plunged into darkness. When another day of Brahma begins, life again becomes manifest.
Each day of Brahma is divided into 14 manvatara periods, each one lasting 71 yuga cycles. Preceding the first and following each manvatara period is a juncture (sandhya) the length of a Satya-yuga (1,728,000) years. Typically, each manvantara period ends with a partial devastation. According to Puranic accounts, we are now in the twenty-eight yuga cycle of the seventh manvatara period of the present day of Brahma.
This would give the inhabited earth an age of 2.3 billion years. Interestingly enough, the oldest undisputed organisms recognised by palaeontologists - algae fossils such as those from the Gunflint formation in Canada - are just about that old (Stewart 1983, p. 30). Altogether, 524 yuga cycles have elapsed since this day of Brahma began. Each yuga cycle involves a progression from a golden age of peace and spiritual progress to a final age of violence and spiritual degradation. At the end of each Kali-yuga, the earth is practically depopulated.