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What evidence suggests that sexual division had developed by the late Precambrian?

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A detailed geologic time scale chart displaying Earth's history from the Hadean Eon over 4.5 billion years ago to the present, organized by eons, eras, periods, epochs, and ages with color-coded columns and corresponding dates in millions of years. — Precambrian The stratigraphic chart of geologic time.

Evidence for the development of sexual reproduction by the late Precambrian is primarily derived from the study of microfossils found in the 900-million-year-old Bitter Springs Formation in central Australia.1

Paleobiologist J. William Schopf identified eukaryotic algae within this formation that exhibit cells in various stages of division arranged into tetrahedral sporelike forms. These structures closely resemble the tetrad of spore cells observed in living plants, which are known to develop through sexual division. This discovery suggests that by the end of the Precambrian, the biological mechanisms necessary for sexual reproduction were established, setting the stage for the subsequent diversification of life during the Phanerozoic Eon.12