[ 69 ] Earth and Space Science GED ® TEST SCIENCE FLASH REVIEW • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Approximately what percentage of the total water on Earth is in the oceans? A. 43% B. 97% C. 73% D. 58% Global climate change is having significant negative effects on oceans, which absorb about one-fourth of the carbon dioxide (CO 2 ) emitted from human activities. This phenomenon is called _______. When CO 2 is absorbed by the ocean, it interacts with saltwater to form carbonic acid. As CO 2 levels in the atmosphere continue to increase, levels of carbonic acid in oceans also increase. This ocean acidification will harm plankton, adversely affect shellfish larvae, hinder the ability of corals to build new reefs, and cause serious food chain disruptions. Coral reefs and estuaries (salty or brackish freshwater that runs into the ocean) sustain 75 percent of all commercial fish and shellfish during some point of their life cycles. One in six people on Earth depend on ocean fish for their primary source of protein. How might a graph show how increasing quantities of CO 2 in the oceans affect humans?