Here's a breakdown:
* Proto-Indo-European: Sanskrit ultimately traces back to Proto-Indo-European, a hypothetical language spoken in the 3rd millennium BCE, possibly in the Pontic-Caspian Steppe region. It's like the great-great-grandparent of Sanskrit.
* Indo-Aryan Branch: Proto-Indo-European evolved into different branches, including the Indo-Aryan branch, from which Sanskrit and many modern Indian languages descend. This branch emerged around 2000 BCE.
* Vedic Sanskrit: Within the Indo-Aryan branch, Vedic Sanskrit emerged around 1500 BCE. This is the language of the Vedic texts, and it's considered the earliest form of Sanskrit. It was mostly a spoken language.
* Classical Sanskrit: From Vedic Sanskrit, Classical Sanskrit developed around 500 BCE, becoming a more refined and standardized language. This form was primarily used for writing religious and literary works, becoming the language of scholars and intellectuals.
So, to answer your question directly:
* Vedic Sanskrit was the earliest form of the language, spoken around 1500 BCE.
* Classical Sanskrit evolved from Vedic Sanskrit and became the primary form used in literature and scholarship.
It's important to note that Sanskrit continued to evolve over time, with various regional and temporal variations. The "form" of Sanskrit depends on which specific period and geographic location you're interested in.