So we have two limestone beds, one of 550 million years old (well, the fossils are, but it suggests that the rock was created around the same area) and another that is 400 million years old. The first one is then older than the second - the correct answer is c!
The answer is
d. preventing weather events
Preventing weather events is not an advantage to tracking changes in the climate system.
Just like convection in air, when denser water sinks, its space is filled by less dense water moving in. This creates convection currents that move enormous amounts of water in the depths of the ocean.