Did You Know?
The solid surface of the Earth that we all stand on is only one of the layers of the Earth. Studies of earthquakes and how they transmit their energy (see Unit E – Earthquakes for further details) have revealed that the Earth is composed of three different layers, each with distinct differences in chemical composition. These three layers are the crust, the mantle, and the core.
- Crust: The crust is the rigid, solid layer that we normally associate with the surface of the Earth. The crust accounts for about 1% of the total volume of the Earth and has an average thickness of about 30 km (about 18 miles), although its individual depth can vary from about 7 km (about 4 miles) under the oceans to more than 70 km (about 43 miles) under mountains. Most earthquakes originate in the crust (see Unit E – Earthquakes for further details).
- Mantle: The mantle is a dense, hot layer of flexible rock that lies directly underneath the crust and has a depth of approximately 2,900 km (approximately 1,800 miles). It accounts for, and is the source for the magma we see coming out of volcanoes. There is a great deal of difference in chemical composition between the mantle and the crust; the mantle is composed of a relatively large concentration of magnesium when compared to the crust.
Word Link
The mantle can be further subdivided into the upper mantle and the lower mantle due to the change in temperature, pressure and plasticity the further you move down to the core.
The structure of the Earth’s interior is often compared to a hard-boiled egg.
- Core: The very center of the Earth lies under the mantle, and is known as the core. The Earth’s core has a radius of 3,480 km (approximately 2,100 miles) and consists primarily of iron. Like the mantle, the core is further divided into two very distinct zones. The inner core has a radius of about 1,220 km (about 760 miles), and is solid. The outer core, with a thickness of 2,260 km (about 1,400 miles), is liquid. It is the movement of iron in the outer core that is responsible for the Earth’s magnetism and its magnetic poles.
Math Link
Calculate and compare the relative volumes of Earth and its inner and outer cores. Go to Math Link...
Try This!
Earth's Magnetism
The intensity (strength) of the Earth’s magnetic field varies a great deal depending on location.
- Click here to return to a view of the Earth’s total magnetic intensity.
- Examine the colors in the scale for magnetic intensity.
- What color corresponds to:
- the strongest magnetic field? The strongest magnetic field has a light pink color.
- the weakest magnetic field? The weakest magnetic field has a deep blue color.
- Rotate the globe and see how the magnetic intensity changes with location.
- Which parts of the globe exhibit the strongest magnetic field? The two Polar Regions (the North Pole and the South Pole) exhibit the strongest magnetic fields.
- Why do you think that these regions have such strong magnetic fields? These regions have such strong magnetic fields because this is where the north magnetic pole and the south magnetic pole are located.
Locating the north and south magnetic poles will provide support for the proper answer for question 3.
- Click here to see the current location of the current north magnetic pole.
- Click here to see the current location of the current south magnetic pole.
- Are the magnetic poles located in intense (strong) magnetic field areas? Yes, the magnetic poles are located in strong magnetic field areas.
- Which part of the globe exhibits a relatively weak magnetic field? The equatorial regions (particularly near South America) have a relatively weak magnetic field.
- Examine the values on the scale for Total Magnetic Intensity.
- What is the range of values in this scale? The scale varies from 22,000 nT to 68,000 nT.
The base unit of magnetic intensity is the tesla (T). Our scale uses the nanotesla (nT) as its unit (one nanotesla = 1 x 10-9 tesla). By way of comparison, the magnetic intensity of a typical refrigerator magnet is 5,000,000 nT, while a human brain has a magnetic intensity of approximately 0.0005 nT.
- Click here to add in the state / provincial boundaries for North America.
- What it the total magnetic field intensity (in nT) where you live? Answers will vary depending on location.