A radical activist who helped set a $1 million fire to protest research on genetically modified crops was sentenced Thursday to nearly 22 years in prison _ even more than the prosecution recommended.

Marie Mason decided to "elevate her grievances beyond the norms of civilized society" through fire and destruction, U.S. District Judge Paul Maloney said. The case _ which was prosecuted as domestic terrorism _ was "about an abandonment of the marketplace of ideas," he added.

The explosion and fire caused more than $1 million in damage to Michigan State University's Agriculture Hall on New Year's Eve 1999.

In her plea agreement, she also admitted causing an additional $3 million in damage through other acts from 1999 to 2003, including destroying homes under construction in the Detroit area and Indiana and setting fire to two boats owned by a man who formerly raised minks.

The 47-year-old Mason, of Cincinnati, had acted on behalf of the radical group Earth Liberation Front, or ELF, which has been implicated in a spate of similar crimes, mostly in the West.

She had pleaded guilty in September to conspiracy and arson after reaching a deal with prosecutors. The prosecution had been aided by Frank Ambrose, her former husband, who cooperated with the FBI.

The investigation was cold until spring 2007, when a man looking for scrap cardboard found gas masks, an M-80 explosive, maps and anti-government writings in a suburban Detroit trash bin.

They belonged to Ambrose, who apparently was trying to shed remnants of his past. The FBI searched his home, and he became an informant, blowing the whistle on himself and Mason and going undercover to record 178 conversations with other activists.

At MSU, Mason and Ambrose targeted a campus office that held records on research related to moth-resistant potatoes for poor parts of Africa. Computers, file cabinets and desks were doused with a flammable liquid. Vapors contributed to an explosion, and the fire got out of control.

The explosion burned Mason's hair and prevented her from finishing the message, "No GMO," on a wall, a reference to genetically modified organisms.

"Pure luck" prevented the couple from being killed, Assistant U.S. Attorney Hagen Frank said. "Did that deter Ms. Mason? Not one bit. She celebrated it. Her community celebrated it."

Prosecutors had recommended 20 years in prison for Mason _ a term that would have been "the most onerous sentence imposed in a case of this sort," Frank said.

Speaking near the end of a three-hour hearing, Mason said she had been "misguided" and was sorry for those who were frightened by her actions. "I meant to inspire thought and compassion, not fear," she told the judge.

Maloney sentenced Mason to 21 years and 10 months in prison and described her as a "high risk" to repeat her crimes.

Defense lawyer John Minock said he would appeal the sentence. "I'm shocked," he said outside court. "It's grossly out of proportion to other cases."

Ambrose was sentenced in October to nine years in prison.

Two people who were aware of the arson but didn't report it were also sentenced Thursday. Aren Burthwick received 14 months in prison and Stephanie Fultz was placed on probation for two years and ordered to perform 100 hours of community service.

In an interview, U.S. Attorney Don Davis tipped his hat to Andy Wishaw, the man who alerted authorities to the unusual things he found in the trash bin.

"This case, like many other cases, was resolved through citizen interaction with law enforcement," Davis said.