Brahma Knowledge, by L. D. Barnett, , at sacred-texts.com
§ 23. Brahma the Destroyer.—As we saw, the Upanishads are full of cosmogonies inherited from Vedic religion; but apparently they have not yet arrived at the belief in a periodical course of alternate creation, maintenance, and dissolution of worlds which later became general in India. The earlier texts several times describe Brahma or some cognate power as consuming his creatures separately; but a collective destruction is nowhere mentioned in them. 1
In the later Vedānta the theory of periodical cataclysms is formally accepted. Again and again the universe is created, and after a time dissolved again into indiscrete potentiality; this cycle of birth and death is without beginning and
without end (§ 12). In the intervals between destruction and the following creation the eternal Veda, with its Brāhmaṇas and Upanishads, rests as a potential force in the thought of Brahma; and at the beginning of creation the ideas contained in it serve as archetypes for the formation of all phenomena in the now emerging universe, and are revealed to inspired sages, its karma-kāṇḍa or practical section (the four Vedas and the bulk of the Brāhmaṇas) to guide men to ritual and consequent worldly welfare, its jnāna-kāṇḍa or theoretical section (chiefly the Upanishads) to teach them the true knowledge of Brahma.
49:1 See especially B.A. I. ii. 1, Ch. I. ix. 1, Taitt. III. 1, Kaṭh. II. 25. Universal dissolution appears first in Śvet. III. 2, IV. 1.