Attorney General Eric Holder gave a green light on Thursday to two states whose efforts to legalize marijuana had been locked in by legal uncertainty for more than nine months. With that announcement, Colorado and Washington -- both of which passed pro-pot initiatives at the polls last November -- can now proceed with establishing a framework for the taxation and regulation of legal weed for adults.

The administration's decision holds clear and immediate implications for the two states, both of which had been hesitant to act too quickly over concerns that the government might decide to enforce federal law, which still considers marijuana an illegal substance.

But the move also, and perhaps more importantly, throws open the gates for other states to pursue similar pot legalization efforts, so long as they include "strong and effective regulatory and enforcement systems." Experts on both sides of the issue have already said they expect to see movement come quickly.

A similar pattern held for medical marijuana. The movement made steady progress up until 2009, when the Obama administration announced it would allow states to implement medical pot laws without federal interference. That promise turned out to be heavily footnoted, but the pledge itself ushered in a flood of ballot and legislative activity that burst the medical marijuana dam over the next four years. Thursday's announcement can be expected to do the same.

Public support for legal pot has surged in recent years at both state and nationallevels, with a majority of U.S. voters now in favor. This suggests that legalization would be most viable in states that allow citizen ballot initiatives. State lawmakers could also potentially take the reins on legalizing cannabis as the issue becomes more mainstream, however, like they did in New Jersey in 2010 with the passage of a bill approving medical marijuana.

Political dynamics are at play, too. Democratic strategists hoping to goose youth- and liberal-voter turnout in 2014 are incentivized to put pot on the ballot, though weed advocates themselves are better off running campaigns during presidential years, when the electorate doesn't skew as elderly as it does during midterms.

Below, the states that are most likely to take the next steps toward legalizing marijuana:

Alaska

Marijuana reformers in Alaska have been hard at work trying to make their state the next to legalize pot. In June, a ballot measure to tax and regulate pot and legalize it for adult recreational use was certified. Organizers must now collect at least 30,169 valid signatures of registered Alaska voters by December 2013, which would ensure that the initiative receives a vote in the primary election on Aug. 19, 2014.

Pot has already been decriminalized and legalized for medical use in Alaska. A survey of Alaska voters taken earlier this year by Democratic-leaning Public Policy Polling found that 54 percent supported legalizing marijuana.

Arizona

In June, marijuana legalization proponents began a campaign to gather the 259,213 signatures they'll need in order to get the issue on the 2014 ballot. The language of the proposed measure is rather expansive, and also includes a system of state taxation and regulation.

Marijuana was legalized in the state for medical use in 2010 by ballot initiative. A poll taken earlier this year found that 56 percent of Arizonans supported legalizing some amount of cannabis.

California

A statewide initiative to legalize marijuana failed in California in 2010, but reformers are hoping to find success in 2014 and beyond. Earlier this month, organizers filed the California Hemp Act 2014, a measure that would legalize cannabis both in its standard and non-psychoactive forms. Beginning Oct. 1, the campaign will have 150 days to gather 750,000 valid signatures from California voters in order to get the issue on the 2014 ballot.

Marijuana has already been decriminalized and legalized for medical use in California. A poll taken earlier this year found that 54 percent of Californians support legalizing pot.

Nevada

Marijuana advocates in Nevada have yet to mount a large-scale effort to get legalization on the ballot in an upcoming election, as most organizers in the state see 2016 as their best chance for a push. The liberal bent of the state makes it a popular target for reformers, however, and it's not yet clear whether Thursday's DOJ decision could increase desire for more immediate action.

Nevada has legalized medical marijuana, and earlier this year the state passed a measure establishing a dispensary system to help increase access for sick citizens. According to a recent poll, 56 percent of Nevadans would favor legalizing cannabis for recreational use if the money raised went to fund education.

Oregon

Medical marijuana legalization advocates in Oregon have already announced plans to campaign for an initiative to be placed on the ballot in 2014. An earlier legalization effort, which was poorly coordinated and widely mocked inside the state, failed in 2012. Organizers believe there is plenty of room for improvement.

Oregon has already decriminalized marijuana and legalized it for medical use. According to a poll taken in May, 57 percent of likely voters in Oregon support a proposal to tax, regulate and legalize marijuana for recreational use.

Maine

The Marijuana Policy Project, a pro-pot advocacy group, has announced Maine as one of its top targets for legalization in upcoming election cycles. An initiative circulating through the state Legislature fell painfully short in a state House vote earlier this year, but MPP has announced plans to help coordinate a grassroots campaign to get a legalization measure on the ballot in 2016.

Marijuana has been decriminalized and approved for medical use in Maine. According to a PPP poll released this week, 48 percent of registered voters in Maine believe pot should be legal for recreational use.

Massachusetts

The deep-blue New England state is being eyed as a prime opportunity for legalization, with marijuana reform advocates pointing to high margins of support for previous pro-pot initiatives. No official campaign for a ballot initiative has been launched yet, though many predict it is only a matter of time.

Massachusetts has decriminalized marijuana and just last November passed a ballot measure legalizing it for medical use. A February PPP poll found that 58 percent of the state's residents would be in favor of legalizing, taxing and regulating cannabis.

Montana

Montana has had a checkered history with marijuana laws. Voters passed an initiative legalizing cannabis for medical use in 2004, but opponents have since taken various steps to amend the measure or repeal it all together. Reform advocates remain hopeful that voters will support full legalization. They wasted no time following the 2012 election, filing a ballot question in hopes of putting the issue before voters in 2014.

There are no recent statewide surveys to gauge current support for pot legalization, though previous polls have showed a majority of Montana voters supporting the decriminalizing of marijuana.

Rhode Island

Marijuana advocates have high hopes that Rhode Island will be one of the first in the next round of states to legalize. This could come through a ballot initiative, but Rob Kampia, the executive director of MPP, recently said the issue could be ripe for state lawmakers to take on. While there's not yet a high-profile campaign to get legalization on an upcoming ballot, the state Legislature did consider a bill on the matter last session. While lawmakers debated the legislation and invited witnesses to testify on its merits, they never held a vote.

Rhode Island recently decriminalized marijuana and passed legalized medical marijuana around 2007. A PPP poll taken in January found that 52 percent of voters in the state support legalizing pot for recreational use.

Vermont

Vermont has made strides to scale back marijuana prohibition over the past year, with a successful measure to decriminalize and a separate bill to establish a system of dispensaries for the state's medical cannabis patients. Observers see the state's strong support for the recent reelection of Gov. Peter Shumlin (D), an advocate for marijuana reform, as a sign that voters could get behind a ballot initiative to legalize. There is no large-scale effort toward this end yet, but a legalization bill was introduced in the state Legislature last session. It didn't receive a vote.

Polls have consistently shown Vermonters to be supportive of efforts to scale back prohibition on marijuana.

Don't believe that whole "men are from Mars, women are from Venus" trope. New evidence seems to support the theory that we're all from the red planet.

For decades, some scientists have postulated that life started on Mars, with experts pointing to the ability of bacteria to withstand harsh conditions as evidence. While the theory that such bacteria hitched a ride on a meteorite and made their way to Earth may seem far-fetched, the idea has gained support from new research unveiled this week at the 2013 Goldschmidt Conference in Italy.

"The evidence seems to be building that we are actually all Martians; that life started on Mars and came to Earth on a rock," Dr. Steven Benner of the Westheimer Institute for Science and Technology said in a statement issued before his presentation at the annual geochemistry colloquium. The institute is located in Gainesville, Fla.

In Florence on Thursday, Benner is expected to report that the oxidized mineral form of the chemical element molybdenum may have been a key to the origin of life. Molybdenum is believed not to have been present on Earth at the time life originated.

"This form of molybdenum couldn’t have been available on Earth at the time life first began, because three billion years ago the surface of the Earth had very little oxygen, but Mars did," Benner said in the statement. "It’s yet another piece of evidence which makes it more likely life came to Earth on a Martian meteorite, rather than starting on this planet."

Under Benner's research, the theory of how life began hinges primarily on two paradoxes:

• The Tar Paradox: All living organisms are composed of organic matter. But how exactly did life sprout from it? If organic molecules come in contact with a source of energy without any outside influences, the matter tends to turn into tar-like material. However, certain elements -- specifically boron and molybdenum -- are capable of stopping this "de-evolution," according to Benner. Previous analyses of martian meteorite material suggested that boron is present on Mars, and, as Benner revealed this week, molybdenum is also believed to have existed on the planet.

• The Water Paradox: Three biological molecules are believed to be essential for life: DNA, RNA and proteins. However, water is known to be corrosive to these macromolecules. Since water likely covered a larger portion of Earth than Mars at the time, the red planet would have been a more suitable environment for the origin of life. "How is it possible that the chemicals that we now have supporting modern life, which is so unstable in water, could have arisen in water?" Benner said last year, according to Discovery News.

Benner's theory that life originated on Mars is unproven, of course. But it's possible that it could be substantiated by evidence collected from the red planet. A team from the Massachusetts Institute of Technology is trying to do just that feat by building a detection tool capable of taking samples on Mars and analyzing them for DNA and RNA.

“It’s a long shot," MIT researcher Christopher Carr said in an announcement of the Search for Extraterrestrial Genomes project in 2011, "but if we go to Mars and find life that’s related to us, we could have originated on Mars."

"Or if it started here," he said, "it could have been transferred to Mars."

As WGBH Radio reported, Carr wants NASA to support the investigation and allow the tool aboard its next Mars Exploration Rover mission, which is set to launch in 2020.

WASHINGTON — The National Security Agency on Thursday disputed a published report that secret intelligence budget files provided by agency leaker Edward Snowden show that the surveillance agency warned in 2012 that it planned to investigate up to 4,000 cases of possible internal security breaches.

The Washington Post, citing documents it said were provided by Snowden, said the NSA's concerns about insider threats were aimed at "anomalous behavior" of agency employees with access to top secret data. The account cited NSA concerns about "trusted insiders who seek to exploit their authorized access to sensitive information to harm U.S. interests."

The NSA concerns were outlined in top-secret documents provided to the Senate and House intelligence committees in February 2012, well before Snowden emerged this summer as the sole source of massive new disclosures about the agency's surveillance operations. The Post released only 17 pages of the entire 178-page budget document, along with additional charts and graphs, citing conversations with Obama administration officials who voiced alarms about disclosures that could compromise intelligence sources and methods.

An NSA spokesman disputed the Post's description of the agency's planned investigation of 4,000 possible security breaches, saying the effort actually amounted to a broad investigation of personnel to lessen the possibility of security risks.

"NSA planned to initiate 4,000 reinvestigations on civilian employees to reduce the potential of an insider compromise of sensitive information and missions," agency spokesman Vanee M. Vines said late Thursday. "Periodic reinvestigations are conducted as one due-diligence component of our multifaceted insider threat program."

Vines said such reinvestigations are required under a 2008 federal directive governing high-security clearances for intelligence workers.

As of Thursday night, the Post had not amended its reporting.

It was not clear from the Post's reporting how many of the 4,000 cases ultimately were investigated or how many posed serious breaches of security. Steven Aftergood, head of a project on government secrecy at the Federation of American Scientists in Washington, questioned whether many of the reported 4,000 cases were credible.

Referring to previous reports that the NSA's classified work force totals nearly 40,000, Aftergood said, "It would be hard to believe that one in every 10 NSA employees is a possible threat." He suggested that many cases might be caused by internal warnings arising from minor internal protocol errors or mistakenly accessed documents.

But aggressive high-profile Justice Department prosecutions in recent years of several former NSA staffers have shown the agency taking a toughened stance in cracking down on possible leaks. "In any case, a number that large is striking," Aftergood said.

The latest revelations also disclosed limited details about the highly classified 2013 intelligence "black budget," which previously only provided a topline of nearly $53 billion. The $52.6 billion intelligence budget described by the Post discloses that the NSA's portion was $10.5 billion in 2013 – outstripped only by the CIA's $14.7 billion.

Aftergood said the CIA's budget growth from $3 billion in the 1990s to nearly $15 billion likely reflects its post-9/11 push into drone warfare and paramilitary operations overseas.

The Post's story also said the NSA and CIA were engaged deeply in offensive cyber operations and had conducted counterintelligence operations against the governments of Israel and Pakistan as well as traditional targets such as Iran, Russia, China and Cuba. The Post also reported that the NSA considers North Korea the hardest intelligence target to crack and said U.S. officials know almost nothing about the plans of North Korean leader Kim Jong Un.