Changes in ocean chemistry and temperature have had a dramatic effect on the diversity of corals and sea anemones, according to a team of scientists who have traced their evolution through deep time. A new study, published Aug. 31 in the journal Nature Ecology and Evolution, finds that reef-building corals emerged only when ocean conditions supported the construction of these creatures' stony skeletons, whereas diverse softer corals and sea anemones flourished at other times. Without a significant change to anthropogenic carbon emissions, the new findings present stark implications for the present and future of hard-bodied corals while suggesting a silver lining for the diversity of some of their softer-bodied relatives.