Is there any hard evidence to show that the earth has a molten core or possibly a hollow core?

Answer 1

Surprisingly the actual inner core is probably solid iron. It's solid due to the intense pressure down there. Around this there is a molten rock outer core, and the movements within this area account for the magnetic field generated by the earth. Above this is the mantle, a semi-molten area within which convection currents cause the plates above them carrying the continents to move. then you've got the crust, 20-odd miles of solid rock that we live on.

Why do we think this?

It's due to the behaviour of seismic waves. When a wave encounters a liquid, or any less dense material, it slows down, and when it encounters a solid, or more dense material, it moves more efficiently. So, by looking at the seismic waves from earthquakes on the other side of the earth, and look at how they've been affected by travelling through the earth, we can get a fair iea of the relative density of the various properties of the core and mantle.

Answer 2

It's all to do with the calculated mass of the earth and evidence supplied, and recorded, by P and S waves during seismic activity, either generated by explosions deliberately, or naturally by earthquakes.

The earth is divided into four main layers: the inner core, outer core, mantle, and crust. The core is composed mostly of iron (Fe) and is so hot that the outer core is molten, with about 10% sulphur (S). The inner core is under such extreme pressure that it remains solid. Most of the Earth's mass is in the mantle, which is composed of iron (Fe), magnesium (Mg), aluminum (Al), silicon (Si), and oxygen (O) silicate compounds. At over 1000 degrees C, the mantle is solid but can deform slowly in a plastic manner. The crust is much thinner than any of the other layers, and is composed of the least dense calcium (Ca) and sodium (Na) aluminum-silicate minerals. Being relatively cold, the crust is rocky and brittle, so it can fracture during earthquakes.

How was the Earth's core discovered? Recordings of seismic waves from earthquakes gave the first clue. Seismic waves will bend and reflect at the interfaces between different materials, just like a prism refracts and scatters light waves at its faces.

In addition, the two types of seismic wave behave differently, depending on the material. Compressional P waves will travel and refract through both fluid and solid materials. Shear S waves, however, cannot travel through fluids like air or water. Fluids cannot support the side-to-side particle motion that makes S waves.

Seismologists noticed that records from an earthquake made around the world changed radically once the event was more than a certain distance away, about 105 degrees in terms of the angle between the earthquake and the seismograph as measured at the center of the earth. After 105 degrees the direct P- and S- waves disappeared almost completely, but slow surface waves and waves taking other paths would arrive from over the horizon. The area beyond 105 degrees distance forms a shadow zone. At larger distances, some P waves that travel through the liquid core would arrive, but still no S waves. The Earth therefore has to have a molten, fluid core to explain the lack of S waves in the shadow zone, and the bending of P waves to form their shadow zone.

You can get a rough estimate of the size of the Earth's core by simply assuming that the last S wave, before the shadow zone starts at 105 degrees, travels in a straight line. Knowing that the Earth has a radius of about 6370 km, you have a right triangle where the cosine of half of 105 degrees equals the radius of the core divided by the radius of the earth.

The fact that the Earth has a magnetic field is an independent piece of evidence for a molten, liquid core. A compass magnet aligns with the magnetic field anywhere on the Earth. The earth cannot be a large permanent magnet, since magnetic minerals lose their magnetism when they are hotter than about 500 degrees C. Almost all of the earth is hotter, and the only other way to make a magnetic field is with a circulating electric current. Circulation and convection of electrically conductive molten iron in the Earth's outer core produces the magnetic field. To make the magnetic field, the convection must be relatively rapid (much faster than it is in the plastic mantle), so the core must be fluid. Much of the energy to drive this convection comes from growth of the solid inner core, with the release of energy as the iron changes from solid to liquid.

God I love Geology.

Answer 3

Volcano lava, the S & P seismic waves, and the movement of the tectonic plates are all good evidence of molten inside to the earth. The plates are still moving, it can be seen at the ocean floor and measured.

Also consider the earth's magnetic field. If there were not molten lava circulating in convection, there would be no magnetic field.

The intense pressure (of the entire weight of the earth) that results in its solid central core makes the idea of a hollow core groundless speculation, with no hint that it is possible.

Answer 4

Just to clarify, the fact that volcanoes produce lava in no way implies that the core of the Earth is molten. Rocks and minerals are capable of being liquefied within the crust (up to about 20Km - 35Km down), which is nowhere even close to being the centre of the Earth.

Chariotmender and Paul D have done a good job explaining current scientific thought.

And oh yes, I love geology too!

Answer 5

There is hard visible evidence to support the idea that the earth has a molten core. Volcanoes are pockets that allow molten lava to reach the surface of the earth.

Answer 6

"The core is probably composed mostly of iron (or nickel/iron) though it is possible that some lighter elements may be present, too. Temperatures at the center of the core may be as high as 7500 K, hotter than the surface of the Sun. The lower mantle is probably mostly silicon, magnesium and oxygen with some iron, calcium and aluminum. The upper mantle is mostly olivene and pyroxene (iron/magnesium silicates), calcium and aluminum. We know most of this only from seismic techniques; samples from the upper mantle arrive at the surface as lava from volcanoes but the majority of the Earth is inaccessible. The crust is primarily quartz (silicon dioxide) and other silicates like feldspar."
I'd say on this evidence, the core is probably solid. Though, I'm not going to go look to confirm this...

Answer 7

The earth has a molten core!

We know this from the techtonic movement of land masses, and also through Geothermal probes.

If the earths core was solid it would alter the whole planet and odds are we wouldn't be here. No gravity!

Answer 8

On the Coast to Coast AM radio program I've heard a few guests assert that the earth has a hollow core and some kind of people live down there, but that sounds incredibly ludicrous to me.

Answer 9

The laws of thermodynamics tells us how long a body such as the earth given its mass ,density and age should take to cool.
The maths simply would not add up unless their was a heat source within the earth itself.That heat source would have to be of such a sufficiently high temperature to melt rock in order to explain the present temperature of the earth.

Answer 10

Of course the earth has a molten core. Where do you think the lava from volcanoes come from?