it's not true that the earliest known representations of erotic scenes previously known were 2,000 years old...there are a number of Greek vases from before 400 B.C. which have various lovemaking scenes shown (including heterosexual), and there is an Etruscan tomb from about 550 B.C. which has a fresco depicting intercourse. There may be some material from Egypt which is much earlier.
There's probably a lot more from around the world, but until the last few decades that sort of thing wasn't often exhibited in museums or published.
Um.....cough cough.
BCE dates grow SMALLER as they get closer to our period in time. 2,000 BCE is much, much older than 400 and 550 BCE.