You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
History_of_India

Context:
The 7th and 6th centuries BC witnessed the composition of the earliest Upanishads. Upanishads form the theoretical basis of classical Hinduism and are known as Vedanta (conclusion of the Vedas). The older Upanishads launched attacks of increasing intensity on the ritual. Anyone who worships a divinity other than the Self is called a domestic animal of the gods in the Brihadaranyaka Upanishad. The Mundaka launches the most scathing attack on the ritual by comparing those who value sacrifice with an unsafe boat that is endlessly overtaken by old age and death.

Question:
When were the earliest Upanishads composed?

7th and 6th centuries BC