X-ray of a cross-section of a coral core
World historians who study environmental history sometimes sometimes seek out atypical sources to conduct their research. While a traditional historian may visit an archive to examine governmental records or a collection of personal papers, an archive for an environmental historian might be a crosscut of a tree showing its rings or an x-ray of a cross-section of a coral core like the image here. Coral adds layers to its outer shell every season and these layers vary according to even small changes in the environment including temperature, water clarity, and rainfall. Both scientists and historians can use this data to better understand how the climate has changed over time. For more on how world historians use the framework of climate and environment to understand the past, read this J.R. McNeill essay on world environmental history.
"Climate Close-up: Coral Reefs," NASA Earth Observatory, https://www.earthobservatory.nasa.gov/features/Paleoclimatology_CloseUp/...