I was listening to channel 9 going transatlantic (either SFO to FRA or IAD to FRA), and near the most eastern part of Canada, the air traffic controller dude said, "Radar service will end here." And they started to say all this technical stuff I could not understand. It seemed like that when planes cross the atlantic, they are at one altitude and never change. Is this correct? What if they encounter horrific turbulence and want to change altitudes? Are there radar monitoring over the atlantic to ensure no mid-air plane crashes happen?

What about over the pacific? Is there radar service?