Before organisms with nuclei evolved life on earth consisted only of unicellular

Prokaryotes

Explanation:

The earliest form of life on earth appeared some billion years ago and consisted of prokaryotes. These prokaryotes primarily contains bacteria, archaea and other microscopic organisms that were single celled and have no nuclei. Most of these prokaryotes were anaerobic as they lived in an environment in which there was no oxygen. Instead of oxygen they used other constituents of atmosphere like sulfur, nitrogen etc.

both male and female gametes are produced by meiosis of the germ cells. therefore, both male and female gametes are haploid. one male and one female gamete unite during the fertilization to form the diploid zygote. in seed bearing plants, pollen grain is the male gametophyte, which produces sperm cells.