Ocean waters has its own level of density which depends of the climate, temperature and most of all the location where it came from. The more the ocean water absorbs heat the more its density as a result it rises above from cold to hot. So the the water from the Antarctica usually is less dense and then become more dense when it goes to the equator which is more hot.
eons,eras,periods,epochs,and ages
Explanation:
it subdivides all time into names of abstract time in decendung order of duration.
If they test more than one variable, they wouldn't know if it was both variables or one variable that was responsible for any observed effect.
I believe the answer is:
Geosphere and hydrosphere
Biosphere and atmosphere
Hydrosphere and biosphere
Atmosphere and geosphere
Hopes this helps! ^_^