The creation of the universe, as described in the Rig Veda, emerged out of Avyakta (Unmanifest) in which everything lay latent. This universe emanates from and recedes into Paramatma in an everlasting process. Creation is described as the union of Purusha (life principle or spiritual factor) and Prakriti (nature or cosmic illusion). Omit one or the other, and there is no creation.
Paramatma is immutable and this universe is in That ONE, as the seedling in a seed, devoid of time, space, cause and effect. On account of the combination brought about by Purusha and Prakriti, this variegated universe came into existence. The process of creation is as follows: From the Unmanifest (Paramatma with Prakriti), at its will, forms Mahat (expressive energy), from Mahat comes Ahankara (individuality or ego), which passes into Aakasa (empty space or sky). From Aakasa results Vayu (air), which is converted into Tejas (effulgence), and Tejas develops into water. From water, earth is formed. Earth yields the plant life, which becomes Anna (life-sustaining substance). Then all the beings appear.
This is the process of creation (evolution). The Sristi, which has followed this course, lasts through its allotted period. At the end of the life of Brahma comes Maha pralaya, when all the beings disappear into the Earth whence they came. The Earth dissolves in water, and water passes off into Tejas. Tejas translates into Vayu and Vayu becomes Aakasa, which merges into Ahankara. Ahankara leads to Mahat and Mahat becomes enfolded into Avyakta (Unmanifest), which is Paramatma with Prakriti, the Great Unexpressed. This is the process of involution.This universe that has passed into Avyakta attains expression again after a period equal to that of its existence, that is, 100 of Brahma’s years. Again it lives through its allotted period and then dissolves. Sristi and Laya (dissolution) take place by virtue of only one-fourth of Paramatma. The other three-fourths is the immortal form into which enter those who attain salvation (Mukti).
We learn also that creation, sustenance and destruction have followed one another since the endless time (Anadi).