What do scientists use to divide the geologic time scale? major divisions in the fossil records major divisions in the sedimentary rock layers evidence for catastrophic events in earth's history major changes in mineral deposits in the rock layers

An insulated 40 ft^3 rigid tank contains air at 50 psia and 120°f. a valve connected to the tank is now opened, and air is allowed to escape until the pressure inside drops to 25 psia. the air temperature during this process is kept constant by an electric resistance heater placed in the tank. determine the electrical work done during this process.