The dome of the Thomas Jefferson Memorial is one of the iconic landmarks on the Washington, D.C., skyline. In recent years, however, the gleaming white rotunda has become increasingly darkened, but not by dirt or mold, as the casual eye might suspect. The culprit is a colony of microscopic organisms, called biofilm, which adheres to stone surfaces and is proving a challenge as the National Park Service investigates how to treat it.

The National Park Service today released a statement to justify the arrest of five people last week for "quietly dancing" in the Thomas Jefferson Memorial. While the statement said the agency "supports dancing and other forms of expression in its parks," it added that in some areas of the National Park System dancing is inappropriate and banned.