Four American astronauts talk about their science experiments and the stunning perspective gained living on the ISS.

Earth's mysterious core is yet again generating headlines as scientists learn more about what lies way beneath our feet.

Located 3,000 miles below the Earth's surface, the inner core is anchored by gravity within the molten liquid outer core. It's believed to play an important role in maintaining the planet's magnetic field.

And scientists have a lot of questions about what's happening at the center of the planet. Is it spinning? Could it reverse directions? How hot is it? What's it made of?

New discoveries are even calling into question whether the core is solid. A new study out this week said that the Earth's inner core is less solid than previously thought.

"What we're observing in this study for the first time is likely the outer core disturbing the inner core," study lead author John Vidale of the University of Southern California said, in a statement. He said the discovery opens a door to reveal previously hidden dynamics deep within Earth's core.

What is the Earth's core?

Earth's diameter is about 7,900 miles. The planet's internal structure comprises four layers: a rocky crust on the outside, then a rocky mantle, an outer core made of magma and a solid inner core. This metallic inner core, about 1,500 miles wide, was discovered in the 1930s.

Both the inner and outer cores consist primarily of iron and nickel. They're extremely hot, with temperatures ranging from 7,200-9,000 degrees F.

The Earth's core affects humans by producing its magnetic field, which protects life from dangerous radiation from the sun, allowing life to flourish on Earth.

"Convection in the outer core sustains the magnetic field that protects us from harsh solar radiation and keeps our atmosphere intact," the American Geophysical Union said.

What don't we understand about the core yet?

As the new study pointed out, scientists are continuing to learn about the interactions between the inner and outer core, and what the inner core is made of.

What have recent studies said?

Studies in recent years have continued to explore the Earth's core. Here's what a few of them have uncovered:

∎ Earth's inner core may have stopped turning and could go into reverse.

∎ Earth's interior is cooling faster than previously estimated, prompting questions about how long people can live on the planet.

According to new research published Monday in the peer-reviewed British journal Nature Geoscience, the surface of the Earth's inner core may be changing, as shown by USC scientists that detected structural changes near the planet's center.

The original aim of the USC scientists was to further chart the slowing of the inner core. "But as I was analyzing multiple decades' worth of seismograms, one dataset of seismic waves curiously stood out from the rest," Vidale said. "Later on, I'd realize I was staring at evidence the inner core is not solid."

Why does it matter? (could anything bad happen?)

Other than producing the Earth's magnetic field, Vidale admitted that what happens to the Earth's inner core has little to no impact to those of us up here on the surface. "I can't imaging anything that would affect us up here," he told USA TODAY.

The Earth's magnetic field does "flip" every few million years, he said, but it doesn't have an impact on people.

One minor impact, he said - which is impossible for the average person to detect - is the influence of the rotation of the inner core on the length of Earth's day, but it's only by an order of milliseconds per year.