Tucked in the Senate tax bill's hundreds of pages is a proposal to open up 1.5 million acres of the Arctic National Wildlife Refuge for oil drilling -- and Senator Lisa Murkowski is very happy.

Murkowski, a Republican, lauded the measure hours after the Senate approved its version of the GOP tax plan early Saturday. The bill passed narrowly along party lines -- by a 51-49 vote with only one Republican voting against it.

"Today's historic vote is yet another milestone in bringing us that much closer to realizing a decades-long dream of opening the 1002 area of ANWR," Murkowski said.

ANWR has been closed to oil exploration since 1980 because of concerns about the impact on the region's caribou, polar bears and other fragile ecosystems.

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The 1002 area, which is thought to contain massive oil reserves, has been the topic of fierce debate since at least the late 1970s.

So far, bids to allow drilling in the area have been unsuccessful.

But Murkowski, like her politician father before her, has lobbied hard to lift the drilling ban. She argues it will spur Alaska's economy and help pay for the tax breaks, which an analysis shows could add more than $1 trillion to the country's national debt.

Alaska's other senator, Republican Dan Sullivan, has also argued in favor of developing there. In a Washington Post op-ed last month, he said the state requires developers to use the "best available technology" and ensure the "protection of our incredible species."

But environmentalists say drilling poses a significant threat to the area's wildlife.

On November 9, more than 30 scientists sent a letter to Murkowski that called on her to ensure the zone remains protected.

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"Based on our experience in the Arctic, we oppose oil exploration, development and production in the Arctic Refuge. Such activity would be incompatible with the purposes for which the refuge was established, including 'to conserve fish and wildlife populations and habitats in their natural diversity,'" the scientists wrote.

After Saturday's Senate vote, one of the co-signers, David Yarnold, called the provision "simply shameful" in a statement.

"The Arctic Refuge isn't a bank," said Yarnold, who's also the CEO of Audubon, an environmental and conservation nonprofit. "Drilling there won't pay for the tax cuts the Senate just passed."

Nothing is set in stone. The House and Senate versions of the tax bill look very different, and a single version will need to be hashed out in a process known as reconciliation. Lawmakers would need to add the drilling provision to the House bill for it to become law.

Both chambers will need to vote again on the final draft.

Correction: The headline on an earlier version of this article incorrectly referred to the part of the Arctic National Wildlife Refuge that would be opened to drilling.