The boundary for ocean acidity was originally at 20% post-industrial, but researchers have now moved it back to 10% as a call to action before entire ecosystems start to disappear. Ocean acidity levels became intolerable and led to more than half of all marine life dying out. Creatures that make their own shells through calcification rely on calcium and carbonate molecules already floating around in the ocean. Species that make their own shells need carbonate ions (CO 3 2-) to bond to calcium, but they can’t access them if they’re already locked up in bicarbonates. In the study, researchers placed pteropod shells in water with carbonate levels adjusted to reflect projected carbonate levels for the year 2100.