Which Veda contains information about the most ancient Vedic age culture?

The Rigveda is the oldest of the four Vedas and contains the most extensive information about early Vedic period religious and social life. Comprised of hymns and sacred texts, it represents the "sacred knowledge" of the Aryan civilization. Importantly, the Rigveda also contains foundational ideas that later developed into India's caste (Varnsystem. According to Brahminic ideology, Varna represents the hierarchical organization of society into different classes.