Was Judgment Day at hand? At noon, it was black as night, there was lunch by candle light, the night birds came out to sing while flowers folded their petals and the animals behaved strangely. They called it 'New England's Dark Day' and it's been a mystery for almost 230 years.

The mystery has been solved, according to researchers at the University of Missouri, who say evidence from tree rings reveals massive wildfires as the likely cause, one of several theories proposed after the event but previously dismissed as 'simple and absurd.'

Limited ability for long-distance communication prevented colonists from knowing the cause of the darkness. It was dark in Maine and along the southern coast of New England with the greatest intensity occurring in northeast Massachusetts, southern New Hampshire and southwest Maine.

In the midst of the Revolutionary War, Gen. George Washington noted the dark day in his diary while he was in New Jersey.

"The patterns in tree rings tell a story," said Erin McMurry, research assistant in the MU College of Agriculture, Food and Natural Resources Tree Ring Laboratory. "We think of tree rings as ecological artifacts. We know how to date the rings and create a chronology, so we can tell when there has been a fire or a drought occurred and unlock the history the tree has been holding for years."

Nearly 230 years later, MU researchers combined written accounts and fire scar evidence to determine that the dark day was caused by massive wildfires burning in Canada.

"A fire comes along and heat goes through the bark, killing the living tissue. A couple of years later, the bark falls off revealing the wood and an injury to the tree. When looking at the rings, you see charcoal formation on the outside and a resin formation on the top that creates a dark spot," said Richard Guyette, director of the Tree Ring Lab and research associate professor of forestry in the MU School of Natural Resources.

The researchers studied tree rings from the Algonquin Highlands of southern Ontario and many other locations. They found that a major fire had burned in 1780 affecting atmospheric conditions hundred of miles away. Large smoke columns were created and carried into the upper atmosphere.

"This study was a unique opportunity to take historical accounts and combine them with modern technology and the physical historical evidence from the tree rings and solve a mystery with science," McMurry said.

Article: "Fire Scars Reveal Source of New England's 1780 Dark Day", International Journal of Wildland Fire.