What’s inside the Earth?

This is a question that many geologists have been asking for centuries, and the reason is because there is no way to look into the Earth and see what’s going on. Yes, humans have drilled deep holes and sampled what was down in the crust of the Earth, but the Earth’s radius is 6371 kilometers and as one goes deeper into the Earth it gets hotter and much higher in pressure. Actually, it’s amazing how much we do know about the interior of the planet Earth.

So how do scientists find out what’s inside the Earth? The answer to this is: they listen to seismic noise created by earthquakes and volcanic eruptions. Noise from an earthquake on the opposite side of the Earth travels through the Earth’s innards, and the way that the seismic waves are changed gives scientist a clue as to what lies inside. The propagation velocity of these seismic waves depends on the density of the layer they go through. The denser the media the more compressed the waves become, and since waves travel at various velocities they expand and compress accordingly.

What we stand on is the crust or the outer layer of the planet Earth. The crust’s depth varies from 5 to 70 kilometers.  Compared to the radius that is over 6000 kilometers, the Earth’s crust is equivalent to a thin eggshell, and this is the solid part. The rest of the planet, excluding the solid iron core, is rather liquidly. Good thing we’re not standing on that. The oceanic crust is different than the continental crust. The crust below the oceans is only 5 to 10 kilometers thick and is composed of basalt, diabase and gabbro. That sounds like three obscure vegetables. Basalt is an igneous volcanic rock and diabase is a sub-volcanic igneous rock. Gabbro is an igneous rock, which is cooled magna. You get the feeling that the crust is actually magna that has cooled, and that’s basically what it is.

The continental crust is made up of less dense igneous rock like granite, and it’s around 3.7 to 4.3 billion years old. The oceanic crust is only 200 million years old. Remember that the Earth is around 4.7 billion years old.

Both the oceanic and the continental crust float on top of the viscous mantle layer and they are still moving around, crashing into one another and in some cases moving away from one another. Continental and oceanic crust collisions are responsible for mountain creation as one crust rides up on the other. That’s why scientists have found ancient ocean fossils on top of Mt. Everest.

The top layer of the crust is composed of sedimentary rock and soil. This is stuff that has been deposited from seas over millions of years.

The real mystery about the Earth is the mantle and the core. The mantle is composed of silicate rock and is divided into two zones, the top and bottom. The top layer is 200 kilometers thick and it’s plastic, meaning that it’s flowing. There is a lower part to this zone that is 120 kilometers thick. A transition layer under this is 410 to 600 kilometers thick. The bottom zone goes down much deeper, about 1800 or so kilometers. There is evidence that a huge amount of water lies in the transition between these two zones, and it’s more that all of the oceans combined.

The mantle varies in composition and density and it contains higher amounts of magnesium, iron and aluminum. These materials have been pushed up to the crust by volcanic activity over billions of years.

Earthquakes occur in the upper part of the mantle and there is quite a bit of drift or dynamic movement associated with the mantle itself. As interesting as this is, the real mystery is the core.

The Earth’s core has two sections: a solid iron inner core and a molten iron outer core. This arrangement is very important to life on Earth because it is this part of the Earth that creates the magnetosphere, the magnetic shield that protects us from the sun’s radiation and particle bombardment. If the core were not acting like it does, we wouldn’t be here. Mars is a good example of a rocky planet with no active core. In other words, without an active core Earth would be a dead arid planet with almost no atmosphere.

The inner core is a ball with a radius of 1,220 kilometers, and the outer spherical core extends out to 3,400 kilometers. The inner core is believed to be a nickel iron alloy and it is also believed to have enough gold and platinum to cover the surface of the Earth to nearly half a meter.

The outer liquid iron core is slowly cooling and adding to the inner core. Seismic data indicates that the inner core is rotating faster than the Earth by one degree per year. This inner core is not uniform and this is responsible for the variances in the Earth’s magnetic field.

The temperature of the outer core ranges from 4,300 K degrees to 8,000 K degrees. This material is a nickel iron mix that flows in eddy currents by convection (caused by heat escaping from the core) and is responsible for generating the Earth’s magnetic field. Needless to say, the dynamics of this magnetic field generation are not well understood.

The strange thing about the magnetosphere that surrounds the Earth is that the poles occasionally reverse. Scientists think that the Earth’s North Pole will become the South Pole and this process has already started. This magnetic pole flipping has occurred before. This is known as Geomagnetic Reversal and the last one occurred around 780, 000 years ago. A brief flip happened 41,000 years ago, but it only lasted 440 years. A full reversal takes at least a thousand years. No one knows why this happens, but it is believed to be caused by spontaneous changes it the dynamics of the outer core’s flow. Something like this could be influenced by plate tectonics or even impact events. No one is sure. Ultimately, the Earth’s core is slowly cooling. What this will do to the magnetosphere is unknown. I don’t want to be around when it happens.

Thanks for reading.