USA Today reported earlier this week that a new study of 500-year-old clams published in Nature Communications shows that the oceans are experiencing changes in ocean chemistry that have not occurred in the last 1000 years. The clam shells have growth rings similar to tree rings that can be related to climate conditions in specific years going back in time. You can read more about how they did the study and what they found at https://www.usatoday.com/story/tech/sciencefair/2016/12/06/500-year-old-clams-oceans-climate/95040372/.
