A treeApril 10, 1874: The first Arbor Day is observed.

April 10, 1985: Ringling Brothers Barnum & Bailey Circus is called out for its display of "Living Unicorns." A U.S. government veterinarian says that the "unicorns" are actually goats with a surgically-implanted horn in the middle of their heads. Humane associations call for a boycott of the circus.

April 10, 2005: Veteran Los Angeles Times reporter Marla Cone publishes her book "Silent Snow." Cone traveled to villages throughout the Arctic, documenting how toxic chemicals from the industrialized world were taking a toll on the food chain for Arctic natives.

Photo: vitroids/Flickr

This feature is compiled by Peter Dykstra, an MNN contributor and publisher of Environmental Health News and The Daily Climate.