The massive Deep Horizon oil spill of 2010 released enough crude oil into the Gulf of Mexico to fill an entire swimming pool about 7 thousand times.

How do we know the damage possibly caused by such a disaster? We could always plan an experiment..... If you worked for the Dept. of Fish and Game in the Gulf States, maybe you would...

You could take a part of the sea floor very nearby the site of the spill, say an area exactly 100 square meters, and count the number of different species that you find. This would be a measure of "Biodiversity", which is generally a good indicator of ecosystem health - in general, the more Biodiversity, the healthier the ecosystem.

Then you could sample an area of the seafloor exactly the same size, but further away (say 1 km) from the spill site, and count the number of species in that site. And then continue sampling the same size area at 1 km intervals, until you reach an area many kilometers away from the spill site where you know the area was relatively undisturbed by the spill.

If you run this experiment,

1) What is the independent variable?
2) What is the dependent variable?
3) What is one very obvious control variable?
4) Why would you want to sample for biodiversity in each of the sites at the same time of day?

And....
5) What is a valid hypothesis that you could have for this experiment?