PHOENIX - Scientists at Arizona State University now think a supervolcano under Yellowstone National Park could erupt far quicker than previously thought.

Until now, scientists believed it took hundreds or even thousands of years for a volcano to go from dormant to fully active. But now, ASU researchers have found evidence that it can happen in just a few decades.

RELATED: Yellowstone supervolcano may blow sooner than thought -- and could wipe out life on the planet

Here are five things you need to know about the supervolcano:

1. It's not active yet:

Geologists know there's a huge magma reservoir under Yellowstone.

But ASU geologist Dr. Christy Till said it's not "active" magma. Till said it's more of a crystalline form waiting for a spark. Yellowstone has seen earthquake swarms, but nothing that would indicate the volcano becoming active.

2. If it does become active, it could do so quickly:

"Quickly" in geological terms means a hundred years or so, barely in a human lifespan. Previously, scientists believed it took centuries.

3. It could wipe out all life on Earth:

But that's the worst-case scenario, and scientists believe it's the rarest of possibilities. A gigantic explosion could blanket entire states with ash and lower the temperature of the Earth. The last time this supervolcano erupted, which was hundreds of thousands of years ago, ash spread all the way to Arizona and beyond.

4. But it probably won't:

Experts believe the supervolcano has a much better chance of experiencing a lot of smaller eruptions if it does turn active, similar to Hawaiian volcanoes.

5. We can predict it:

Not down to the day, but Till said geologists can predict volcanic eruptions months or even years in advance. That would give authorities plenty of time to evacuate anyone who needs to be evacuated.