We use oxygen ice to work out how the rainfall has changed but also how temperatures change over the last however many years. And oxygen ice tops work because as the coral sits in its little water column, it sits in the surrounding water and as the temperature changes, the more water evaporates off the top and this changes the oxygen and concentration in the water. So as temperature increases, you have more evaporation. This influences the stable oxygen isotopes in the water. Oxygen has two isotopes. It has a heavy isotope which is oxygen 18 and a lighter isotope oxygen 16. And so when that evaporation occurs, it evaporates off that lower oxygen isotope. It's preferentially so first and it'll leave the heavier isotope in that water column. And same when it rains. So when it rains, it'll rain the lighter oxygen isotope first and then that heavier isotope. And this is what we read. So as oxygen isotopes drop, we have temperature and vice versa. And it works the same way for rainfall. So if we have a higher rate of rainfall, there's more water in that water column and we have oxygen isotopes change through that.