Evidence of Aryabhatta
Aryabhata was a great scientist and Mathematician well known all over the world. This is because he was the one who made the worth of Zero well known to the world which was hidden in the texts of Vedas and Astronomy. He men tioned his time in his work named Aryabhatiyam.
The sloka in his work is as follows:- षष्ट्यब्दानां व्यतीतास्त्रयश्च युगपदः। त्र्यधिका विंशतिरब्दास्तदेव मम जन्मनोऽतीताः॥ (Aryabhatiyam Kriyapada sloka 111-10)
In the Kali Yuga, he said that 23 years had passed by the time of 60 x 6 = 360 years. From this, it is understood that there were great scientists in India even in ancient times and that the calculation of Kali Yuga years existed since then. The above verse is from an unpublished manuscript. In the printed book, there is a different version of this verse. According to that version as well, it is understood that he referred to the KaliYuga years as Kali Shaka.षष्ट्यब्दानां व्यतीतास्त्रयश्च युगपदः। त्र्यधिका विंशतिरब्दास्तदेव मम जन्मनोऽतीताः॥
(Aaryabhatteeyam 111-10-11)
In the Kali Yuga period, 3600 years have passed. It has been 23 years since I was born. That would be A.D. 21-3-499
यस्मिन् कृष्णो दिवं यातस्तस्मिन्नेव तदाहनि।
प्रतिपन्नं कलियुगमिति प्राहुः पुराविदः॥
The great works like Bhagavata Mahapurana mentioned the beginning of Kaliyuga is when Lord Krishna became invisible (12). The calculation of Kaliyuga is 5124 years as recorded in the Almanac. The counting moves further every year in the name of Kalisaka.