By gathering volunteers' measurements of marble gravestones of different ages around the world, scientists hope to produce a world map of the weathering rates of those gravestones and thereby better understand how the atmosphere has been changing. The study, called EarthTrek, is developed and managed by the Geological Society of America's (GSA) Education and Outreach group in partnership with organizations around the globe.

GSA says the weathering rates of gravestones indicate changes in the acidity of rainfall between locations and over time. The acidity is affected by air pollution and other factors, and could be used as a measure of changes in climate and pollution levels.

This project has been divided into two levels of data collection. The first is the Graveyard Data level (the location of graveyards) and requires volunteers to log GPS coordinates. The second level - Gravestone Data level (the measurement of the weathering of marble gravestones) also requires a micrometer.

Volunteers are asked to complete the first or both tasks, but GSA advises that before you purchase a micrometer (available through the EarthTrek online store, at hardware and some hobby stores) that you make sure that you can locate the right type of gravestone - marble.

Collecting the location data of the graveyards is also an important part of this project, even those that do not contain marble gravestones.

What is "weathering"?

Raindrops are not pure water but also contain contaminants. When rain is combined with the dust that settles on the gravestones, this mild “acid rain” can chemically affect the materials it comes into contact with – called weathering. The amount of weathering that occurs from place to place differs and may be changing over time.

Marble is a common stone used to make gravestone and is mostly made up of the mineral calcite, which reacts with any acid, including the weak rainfall acids, and dissolves. This means that over time, marble headstones are slowly weathering away and this is what the project aims to measure.

Two measurement methods

There are two preferred methods volunteers can use in this project to measure the weathering rate in marble gravestones.

Lead lettering method - measure the rates of weathering on marble gravestones that have lead lettering. When these gravestones are created, letters are carved into the stone and then lead is gently tapped into the letters. The stonemason then polishes the gravestone smooth so that the lead letters and the surface of the marble are flush (exactly the same height).

The lead in the lettering isn’t as susceptible to weathering as the marble so eventually the lead lettering appears to stand up from the surface of the marble. By measuring the distance from the top of the lead letters to the weathered marble, and recording the date of the gravestone, scientists at GSA can work out a weathering rate over time of the marble. Because they can find gravestones of different ages, they can also work out if the rate has changed over time.

Thickness method – while not as accurate as the previous measurement method, this assumes that when the marble gravestone (without lead lettering) was constructed it was cut and polished to a constant thickness. By measuring the thickness of the same headstone at the bottom and top, researchers can determine if there has been a change in the thickness over time.

So, if you find walking through cemeteries interesting, why not put your interest to good use and join the volunteer EarthTrek program. It's free to participate.

GSA is a global professional not-for-profit society with a growing membership of more than 22,000 individuals in more than 97 countries. Its headquarters is based in Boulder, Colorado, USA.