Tangle writes:
It takes about 1,000 years to build 1-10 cm of chalk (depending on type and condition). So if we started today, and use the fastest rate, it would take 4 million years to build my chalk cliffs.
As I understand it, the reason it takes so long is because the smaller the particle size, the longer it takes to settle to the bottom (Stokes' Law). Since we know the particle size today, we can calculate the time.
If somebody can elaborate on this, it might help to short-circuit any claims that, "it happened in the past so we can't possibly know anything about it."