As a geologist I will retort that if Minecraft environments had eroding surfaces like real life does then that bedrock would also be visible at the surface. Outcrops are just areas that are experiencing erosion rates faster than areas that are overlayed with soil. That said, there are a cool Minecraft programs for geological processes that have been shown to be educational.
I’ve had many hundreds of hours of Minecraft these past few years but… What’s layer 4?
Y-level. Before 1.18 the top layer containing bedrock (ETA: in the overworld) was y=4.
They changed the height of bedrock?
bedrock now spawns around Y=-60, give or take a few blocks
Why would they move the bottom of the world below 0 instead of just moving sea level upwards?
In early snapshots, they simply extended the build limit upwards like you suggested, so when people loaded their old worlds in they started complaining about kilometer-high walls generating in every direction
Why didn’t they just move all the old stuff up?
that would require moving every single thing up which would break a lot of stuff like mod/plugin data
Compatibility with existing worlds
Geologists clearly use custom world generation rules.
-60 since 1.19 or something