These civilizations have been dated from 3300 BC to 1300 BC. At one stage they were thought to have suddenly ended due to an Aryan invasion, though archaeologists now believe it was more likely due to climate change. Ultimately though, nothing is certain in the world of archaeology, at least until the next find, or developments in science.
Yoga's origins as being from the Vedic shastras, or vedic religious texts, which are the foundation of Indian Hinduism. The Vedic texts were created from 500 BC, and the Rigveda is believed to have been completed by 1500 BC. The Rigveda is one of several principle early vedic texts. The Rigveda, Samaveda, and Yajurveda were used by the Brahmins, a caste that were usually priests, or allowed to be priests, in the days when the caste system originated.
A lot of these texts were concerned with sacrificial rituals. There are sacrificial prayers, incantations, and elements related to magic, to name a few aspects of the subject matter. These are now viewed symbolically, or philosophically, although they were presumably intended more literally at the time. But the word "yoga" was discussed in the RigVeda. In it, there is mention of 'yoking' our mind and insight to the 'Sun Of Truth' (David Frawley, a Vedic scholar).
Yoga is also discussed in the Bhagavad Gita, where Krishna describes 4 types of yoga:
The Bhagavad Gita is believed to have been written between the 5th and 2nd century BC. In the Gita, the goal of yoga is the realization of Brahman, or the Divine Essence. Whilst the paths to achieve this for individuals may be different, the essence of coming to an unequivocable knowing of the Oneness of the Divine, and oneself within this fundamental reality, is the same.
"The Gita addresses the discord between the senses and the intuition of cosmic order. It speaks of the Yoga of equanimity, a detached outlook. The term Yoga covers a wide range of meanings, but in the context of the Bhagavad Gita, describes a unified outlook, serenity of mind, skill in action, and the ability to stay attuned to the glory of the Self (Atman), which is of the same essence as the basis of Being (Brahman)."s