Earth's Core Help (page 2)
Introduction to the Earth's Core
Found beneath the mantle is the very center of the Earth. It is made up mostly of iron with a smattering of nickel and other elements. Under extreme pressure, the core makes up about 30% of the total mass of the Earth. It is also divided into two parts, the inner and outer core.
The core is the center part of the Earth and is actually divided into an outer core and inner core. Seismological research has shown that the core has an outer shell of about 2225km thick with an average density of 10 g/cm 3 . The inner core, which has a radius of about 1275km, is solid with an average density estimated to be 13 g/cm 3 . Temperatures in the inner core are estimated to be as high as 6650°C.
The measurement of earthquake waves has suggested that the outer core is fluid and made of iron, while the inner core is solid iron and nickel. The solid center, under extremely high pressure, is unable to flow at all.
The Earth acts as a giant magnet with lines of north/south magnetic force looping from the North Pole to the South Pole. Ancient sailors noticed and used this magnetism to chart and steer a course. Their earliest compasses were just bits of magnetic rock, called magnetite , placed on a piece of wood floating in a dish of water. These adventurers knew with tested certainty that every single time the stone was moved to a different direction, its north end would return to point to true north. They didn’t know why, but trusted their lives to this knowledge.
The magnetosphere is the region of space to which the Earth’s magnetic field is limited by the solar wind particles, also called solar plasma , blowing outward from the Sun and stretching to distances of over 60,000km from the Earth. Solar plasma, a gaseous matter made up of freely moving ions and electrons, is electrically neutral overall. It is created in the solar atmosphere (corona) and is continuously blowing outward from the Sun into the solar system. Since the first spacecraft and satellite orbits around the Earth, nearly 50 years ago, a lot has been learned about the interaction between the magnetosphere and the solar wind.
The magnetic field around the Earth is formed by the rotation of the inner core as a solid ball, the different currents in the liquid outer core, and the slower currents of the mantle.
The Earth’s magnetic field is kept going by this circulation of molten metals in the core. Scientists believe that the iron–nickel core and its ever moving energy changes into electrical energy. Extreme heat and chemical interactions increase electrical currents and magnetism. The Earth’s spin about its axis controls currents and creates the magnetic poles.
Smaller currents, called eddies , have an added effect that are thought to bring about the switch in the magnetic rotation. Currently, this magnetic rotation is moving counter-clockwise, but about every million years, something makes it change and rotate in the opposite direction. The polar magnetic current is called the magnetosphere . Figure 1-9 shows the powerful circulation of magnetic currents surrounding the Earth.
Fig. 1-9. The magnetosphere of the Earth extends from the north and south poles.
The magnetosphere extends far beyond the Earth’s atmosphere out into space.
The magnetic poles and the geographic north and south poles aren’t in the same place. The geographic top and bottom points of the globe are always in the same place, but the magnetic poles move around. Currently, the magnetic pole appears to be moving at a rate of 15km per year. The magnetic North Pole today, is in the Canadian Arctic between Bathurst and Prince of Wales Islands or about 1300km from the geographic North Pole.
The South Pole moves around too. It is most recently located off the coast of Wilkes Land, Antarctica roughly 2550km from the geographical South Pole.
The location of the magnetic poles can be figured out from the study of rocks with magnetic particles. The rocks’ particles are still aligned with the magnetic poles that existed when they were formed. From studying these rocks, scientists have learned that the magnetic North Pole has moved, over the past 500 million years, from just north of the Philippines in the Pacific Ocean to its more northern location today. Actually the poles are in the same place, but the crust’s movement makes their locations appear to migrate like birds.
The magnetic characteristics of underground formations can be measured to figure out geological and geophysical information. This is done through the use of magnetometers , which are instruments that measure small differences in the Earth’s magnetic field. The first magnetometers were big and bulky, and could only survey a small area. In 1981, however, NASA launched a satellite, equipped with magnetometer technology. This satellite, known as MAGSAT , could take magnetic measurements on a continental scale. It allowed geologists to study underground rock formations and the Earth’s mantle. MAGSAT also provided clues to landmass movements and the location of deposits of natural gas, crude oil, and other important minerals.
Geophysicists also measure and record the difference in the Earth’s gravitational field to better understand underground structures. Various underground formations and rock types have different effects on the Earth’s gravitational field. By measuring minute differences between formations, geophysicists can study underground formations and get a clearer idea of what types of formations lie below ground, and if they contain resources like natural gas.
If sailors were around to navigate the Earth’s oceans millions of years ago, their compasses would have still pointed to the magnetic North Pole or “true north.” However, they would have sailed to entirely different places on the wandering and shifting crust than they would have today when following the same compass. The Earth is just not the same as it was millions of years ago. A geologist’s job is to figure out how it has changed and try to predict what it will do in the future.
Now that you have a general idea of the birth and characteristics of our home planet, let’s study the forces that have continued to shape the Earth since those early days.
Practice problems of this concept can be found at: Planet Earth Practice Test
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