1. if you find a rock in the hills that contains a trilobite fossil, what might that fossil tell you about the hills?
2. why do geologists believe that volcanic activity was more common in the past than it is today?

places of higher salinity. there are parts of the ocean where hardly any rain falls but warm dry winds cause lots of evaporation. this evaporation removes water – when water vapour rises into the atmosphere, it leaves the salt behind, so the salinity of the seawater increases. this causes the seawater to become denser.