Source: Geological Society of America. Adapted with permission.
Raindrops contain more than just water. In addition to the small particles of dust around which water drops form, raindrops can contain chemicals found in the atmosphere. Often rain is slightly acidic. This “acid rain” can chemically affect (weather) materials it touches. The amount of weathering differs from place to place and changes over time.
Marble, a stone commonly used to make gravestones, is mostly made up of the mineral calcite. Because calcite is a carbonate mineral, it reacts with any acid, including weak rainfall acids. Over time, therefore, marble headstones slowly wear away. The weathering rates of gravestones show differences in the acidity of rainfall between locations and over time, due to factors such as pollution and changes in climate.
The Gravestone Project, part of the global citizen science program called EarthTrek (www.goearthtrek.com), is seeking volunteers to visit cemeteries around the world and collect scientific data on how marble gravestones are weathering.
The second way uses marble gravestones that were made by pouring lead into the carved letters and polishing them flat. Because lead does not weather as quickly as marble, you can measure the distance between the marble and the lead.Once you collect and report the weathering data, scientists can use this information to produce a weathering map of the world. This map indicates how weathering rates of marble gravestones differ from place to place and change over time. The scientists leading the Gravestone Project have developed a set of protocols to help you collect accurate data. See the protocols at www.goearthtrek.com/Gravestones/Gravestones.html.