The word "bang," in relevance to sex, didn't start out from just anywhere. It actually began with the first sexually reproducing multi-cellular organism known as Bangiomorpha. I guess you can say it was the first sex joke in history -- either that or I am a bit immature. According to Nicholas J. Butterfield's article "Bangiomorha pubscens n. gen., n. sp.: implications for the evolution of sex, multicellularity, and the Mesoproterozoic/ Neoproterozoic radiation of eukaryotes" in GeoScience World, these multi-cellular organisms are identified as bangiacean red algae based on their cell-division patterns.
Fun, right? Now, cell division is a far more complex process than we may think. We can't just take a knife right down our cells as if we were cutting an apple and say "wala" they are divided. First of all, our cells are microscopic so they are far too small to see and conduct that process. Sorry to disappoint you pre-med students out there. And second of all, they must require a far more complex process than that to be sexually reproducing.
Student: So what you are saying, right, is that Bangiomorpha are the first sexually reproducing organisms?
Writer who is pretending to be a teacher: That is quite right what I am saying. With a more complete fossil record of other Proterozoic eukaryotes, Bangiomorpha fossils mark the beginning of other major protistan radiation near the Mesoproterozoic/ Neoproterozoic era.
Student: But what are the indications that they are sexually reproducing?
Writer who is pretending to be a teacher: Well, student, they have "differential spore/ gamete formation" to show that they are sexually reproducing as opposed to prokaryotes. This is all noticeable in the fossil record.
If you have taken an introduction to biology class, you should be familiar with the fact that cells divide to create a total of four daughter cells in the process called meiosis. Meiosis is the process of creating sexually reproducing cells. The first sign of this just happens to be Bangiomorpha.
Eukaryotes are what made sexual reproduction possible; Bangiomorpha seems to be the first sign of this. Sexual reproduction is critical for life to exist; for species to continue to exist. For early life in particular, sex was not as much critical for genetic recombination, but to create complex multicellularity. Science is another form of innovation. It is a way of making our world more evolved.
It is important to be aware of how our lives became possible. Without the onset of eukaryotes, we would not be here today.