Why do atheists claim to know all about science BUT don't know that the earth had a water canopy around it?
before the flood and that it is the reason for the flood????

here are the FACTS concerning the True Science of the great flood.
1) Earth was water vapor canopy surrounding the earth before the flood.
2) water was stored in small ice particles distributed in equatorial rings around the earth similar to those around Venus.
3) water canopy collapsed (Genesis 7:11, 8:2) and fell as rain.
4) Volcanic eruptions associated with the breaking up of the fountains of the great deep (Genesis 7:11) thrown dust into the water vapor canopy, causing the water vapor to nucleate on the dust particles and make rain. (Genesis 7:12)
5) water canopy would also affect the global wind systems. Also, the mountains were almost certainly not as high before the flood as they are today.
6) there was no such thing as "arctic" and "antarctic" before the flood.