Geocaching.com has announced that tomorrow, October 14th, is "International EarthCache Day". An EarthCache site is a special place that people can visit to learn about a unique geoscience feature or aspect of our Earth. You log your "find" by answering specific geological-related questions posed by the cache hider. There is no container to find at ground zero, just a unique geological formation or feature to observe.
It is not clear whether a new souvenir badge will be added to your profile page on geocaching.com if you log an earthcache, or attend an earthcache event tomorrow, but it does not appear to be the case.
You can learn more about earthcache day on the gc.com facebook page, and find out more about earthcaches in general from earthcache.org.
Happy Earthcaching. Cache On!