For decades, geologists have known that the Marcellus Shale was rich with gas. And oil and gas companies have long extracted resources from Pennsylvania. A combination of technological, regulatory, economic and political factors have brought the industry to where it is today. Here are some milestones. (Note: Time line is not to scale.)

1859: Edwin Drake's crew drills the nation's first oil well in Titusville, PA.

1940s: Halliburton pioneers hydraulic fracturing, or "fracking." Workers pump millions of gallons of water and other chemicals under very high pressure into shale, creating cracks where the natural gas can come out.

1984: Pennsylvania passes the Gas Act, which exempts gas companies from local zoning. The Department of Environmental Resources, now reorganized as the Department of Environmental Protection, will regulate drilling.

1993: Gas companies employ a technique called horizontal drilling in Texas' Barnett Shale, which is as deep as-and in some places deeper-than the Marcellus.

1997: Eight years after Alabama residents complained that gas drilling contaminated their water wells, the U.S. Court of Appeals for the 11th Circuit in Atlanta orders the EPA to regulate hydraulic fracturing under the Safe Drinking Water Act.

2000: The EPA begins a study of the threats to water supplies from fracking. Later that year, former Halliburton CEO Dick Cheney is declared the next vice president of the United States.

2003: Range Resources drills the first horizontal Marcellus well in Washington County, PA.

2004: President George W. Bush and Vice President Cheney win a second term. Over the objections of some staff scientists, the EPA declares fracking of little concern.

2005: Congress exempts fracking liquid from the Safe Drinking Water Act. Gas companies do not have to disclose what is in the gels and chemicals used to extract gas.

2006: Cabot landmen arrive in Dimock, a northeastern Pennsylvania township, offering $25 an acre, plus 12.5 percent of royalties. Many landowners sign up; Cabot drills only one well.

2007: Cabot drills its second well in Dimock.

January 2008: Geologists Terry Engelder, of Penn State, and Gary Lash, of SUNY-Fredonia, publish a paper estimating that 50 trillion cubic feet of natural gas could be extracted from the Marcellus Shale-enough to supply the nation for two years. This is much higher than all previous estimates.

July 2008: The governor of New York orders the state's Department of Environmental Conservation to update its laws to better regulate drilling. The decision puts a de facto moratorium on drilling in New York's Marcellus Shale as a battle heats up over the drilling's possible affects on New York City's water supply.

December 2008: The DEP receives 451 drilling applications, about five times more than it received from 2003 to 2007 combined. By now, Cabot has drilled 30 wells in Dimock.

January 2009: Dimock resident Norma Fiorentino's water well explodes. She and other neighbors notice discolored and bubbling water. They beg Cabot for bottled water. Cabot refuses.

March 2009: The DEP takes the responsibility of issuing grading and sediment permits away from the county Soil Conservation Districts.

April 2009: The gas industry intensifies lobbying efforts to oppose a proposed tax on the gas they extract. Tax advocates point out that every state but California taxes drilling.

April 2009: U.S. Sens. Bob Casey, D-PA, and Charles Schumer, D-NY, introduce the Fracturing Responsibility and Awareness of Chemicals Act, known as the "Frack Act," which would require companies to disclose what is in fracking fluids.

August 2009: A Penn State study estimates that, in 2009, drilling in the state will create more than 48,000 jobs, generate $3.8 billion in value-added dollars, and bring in $400 million in state and local tax revenues. It called the environmental effects "minimal." The gas lobby paid for the study.

Sept. 8, 2009: The Chesapeake Bay Foundation appeals three permits that the DEP approved.

Sept. 15, 2009: Chesapeake Energy offers Wyoming County landowners $5,750 per acre, plus 20 percent royalties. The company pays for the courthouse to be open extended hours so that all of the deeds can be recorded.

Sept. 16, 2009: Dimock residents meet with Cabot and again beg for water. That same day, Cabot has two spills at its Heitsman well.

Sept. 22, 2009: Cabot has a third spill at the Heitsman site, for a total of 8,000 gallons of fracking waste released into a Dimock creek.

Sept. 22, 2009: The DEP orders Cabot to stop fracking until it submits an updated plan.

Oct. 7, 2009: Range Resources, which spent nearly half a million dollars lobbying against the proposed gas tax, hires K. Scott Roy, a top aide to Pennsylvania Gov. Ed Rendell, as vice president of government and regulatory affairs for the Marcellus Shale Division. Rendell initially supported a gas tax, but changed his mind.

Oct. 9, 2009: Governor Rendell signs the $27.8 billion state budget without a gas tax. Instead, the state will raise $60 million by opening more state forestland to gas drilling.

Oct. 16, 2009: The DEP allows Cabot to resume fracking.

Oct. 22, 2009: The DEP fines Cabot $56,000 for its three spills, which it says violate the Clean Streams Law, Solid Waste Management Act and Oil and Gas Act.

Oct. 26, 2009: Oct. 26, 2009 - The Scranton Times runs an article in which Fiorentino describes how she has to spend her fixed-income on bottled water. Within hours, Cabot calls to say they will buy her bottled water. A Cabot spokesman says the events are unrelated.

Oct. 28, 2009: The Chesapeake Energy Co.'s CEO promises that his company will not drill in the New York City watershed.

Oct. 29, 2009: The DEP revokes the three permits that were the subject of a Chesapeake Bay Foundation's lawsuit, citing "technical deficiencies."

Nov. 5, 2009: DEP fines Cabot $120,000, requires additional oversight over its casings and drilling, and says the company must come up with a permanent water solution for the 13 families affected by the well pollution. Nearly a year after her well exploded, Norma Fiorentino relaxes.