EARTH SCIENCES - Notable Research and Discoveries Part 3 ppsx

lines of force are associated with a magnetic fi eld—a region of space in which magnetic forces act.. Earth’s magnetic fi eld is also known as the geomagnetic fi eld geo is a Greek prefi

1 The U.S government establishes the USGS.

1 The German scientist Emil Wiechert (1861–1928)

rounded by a rocky mantle

hypothesizes that Earth contains a metal core sur-eploring earth’s Depths

10 The Croatian researcher Andrija Mohorovičić

(1857–1936) analyzes seismic waves and finds the Mohorovicic discontinuity, which separates Earth’s crust and mantle

11 The German researcher Alfred Wegener (1880–1930)

proposes that Earth’s continents drift over time

11 The German seismologist Beno Gutenberg (1889–

1960) uses seismic waves to locate the depth of the mantle-core boundary at about 1,800 miles (2,900 km) below the surface

1 The Danish seismologist Inge Lehmann (1888–

1993) analyzes seismic waves and discovers dence for a boundary between a solid (inner) and liquid (outer) core, which she places at a depth of about 3,200 miles (5,150 km)

evi-1

The Project Mohole, an attempt to drill into the Mo-horovicic discontinuity, begins The project would last eight years but fail to attain its primary goal

1 The Canadian researcher J Tuzo Wilson (1908–93)

proposes the theory of plate tectonics

10s

The Russian scientists drilling in the Kola Peninsu-est hole ever drilled

la reach a depth of 7.6 miles (12.26 km), the deep-00 The Japan Agency for Marine-Earth Science and

Technology (JAMSTEC) begins testing the drilling

Dixon, Dougal The Practical Geologist: The Introductory Guide to the

Basics of Geology and to Collecting and Identifying Rocks New York:

Simon and Schuster, 1992 This book introduces the subject of geology

eploring earth’s Depths

Mathez, Edmond A., ed Earth: Inside and Out New York: New Press,

2001 Written by a team of experts, this highly informative book

0847.htm Accessed May 4, 2009 Vladimir Kostoglodov of the Na-tional Autonomous University of Mexico and his colleagues spotted

an unusual reversal in the motion of the plate at Guerrero, Mexico

——— “Deep-Sea Drilling Yields Clues to Mega-Earthquakes.” News

release, December 18, 2007 Available online URL: http://www

sciencedaily.com/releases/2007/12/071212201948.htm Accessed May

4, 2009 A description of the findings of an expedition of the scientific

drilling vessel Chikyu to the Nankai Trough.

University of California Museum of Paleontology “Plate Tectonics.”

Available online URL: http://www.ucmp.berkeley.edu/geology/



lines of force are associated with a magnetic fi eld—a region of space in which magnetic forces act Earth’s magnetic fi eld is also known as the

geomagnetic fi eld (geo is a Greek prefi x meaning Earth) According to

Gilbert, compasses align themselves to the geomagnetic fi eld

Gilbert’s ideas seemed to explain the behavior of compasses Yet navigators began noticing that Earth’s magnetic fi eld was not constant

Instead of always pointing in exactly the same direction, compasses deviated, changing direction slightly over the years Th ese shift s were diffi cult to understand if Earth was a fi xed bar magnet Th e origin and nature of Earth’s magnetic fi eld appeared to be more complicated

Geologists study Earth’s magnetic fi eld because it is critical for many applications—although global positioning system (GPS) receivers have largely replaced compasses for navigation these days, Earth’s magnetic

gies Earth’s magnetic fi eld also reveals much about the structure of the planet Th e previous chapter described Earth’s core, which is mostly made of iron Earth’s core is the basis for the planet’s magnetic fi eld, but the mechanism is not as simple as Gilbert envisioned Th is chapter ex-plains how and why scientists have reached this conclusion Although researchers have made progress in understanding the complicated phe-nomena underlying Earth’s magnetic fi eld, much crucial information remains undiscovered at this frontier of Earth science

fi eld infl uences radio communication and other important technolo-IntRoduCtIon

Magnetism is closely related to electricity, although this relationship is not obvious and took many years for scientists to appreciate In 1820 the Danish physicist Hans Christian Oersted (1777–1851) found that an

electric current produces a magnetic fi eld A current is a fl ow of elec-tric charges, and when charges fl ow along a conductor such as a wire, the conductor creates a magnetic fi eld Oersted measured this magnetic

fi eld by the force it exerted on a compass needle in its vicinity In the 1830s the British scientist Michael Faraday (1791–1867) discovered

a similar but opposite relation—a changing magnetic fi eld induces an electric current in a conductor Th e Scottish physicist James Clerk Max-well (1831–79) formulated a set of equations in the 1860s describing the

Origin and Variability of earth’s Magnetic Field

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mathematical behavior of tric and magnetic fields Maxwell showed that these fields arise from interactions of electrically charged particles—these interactions, and the associated forces, are known

elec-as electromagnetism

A magnet exerts a force on other magnets, although the na-ture of the force depends on the magnets and their orientation

Common magnets such as a bar magnet are dipoles, meaning they have two magnetic poles or ends, one of which is called north and the other south (These terms re-flect the importance of compasses

in the early studies of tism.) As one magnet approaches another, the north pole of each magnet attracts the south pole of the other magnet, while the north pole repels the north pole of the other The same is true for south poles, which attract the north pole of another magnet but repel the

magne-south pole Magnets also tend to affect metallic objects in their vicinity,

especially ones containing iron, even if those objects do not appear to

be strongly magnetic

What gives a magnet its magnetic properties? Notice that there are several types of magnets One type, sometimes called a permanent mag-

All magnets and magnetic forces involve electric charges, as Max-

electromagnets Iron magnets derive their properties from ferromag-netism (Ferrum is a Latin word meaning iron.) Ferromagnetism is not

Iron filings align themselves

to a bar magnet’s field,

showing the lines of force

(Cordelia Molloy/Photo

Researchers, Inc.)

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located the north magnetic pole in 1831 As can be seen in the figure on

(opposite page) Earth’s magnetic field behaves approximately as if it were

coming from a bar magnet buried in the planet, although the magnetic

poles are at a slight angle (roughly 11 degrees) from the axis of rotation

(North and South Poles).

Origin and Variability of earth’s Magnetic Field

Island, about 155 miles (250 km) northwest of Amundsen’s discovery

Geological Survey of Canada

The GSC was created in 1842 A year earlier, the legislature

of the Province of Canada, which at the time consisted of

parts of modern day Ontario and Quebec, resolved to fund

a geological survey of the province, and the agency born to

carry out this survey became the GSC The motivation for

establishing GSC was similar to that which was to lead to

the creation of the USGS in Canada’s southern neighbor in

1879—to assess the natural resources of the land Canada

possesses considerable natural resources and is among

the world’s leading producers of copper, zinc, nickel,

ura-nium, and other minerals Oil and natural gas deposits in

and around the country are also rich; in 2006, for example,

Canada was the leading exporter of crude oil to the United

States, accounting for about 20 percent of the total U.S

imports for this crucial energy resource, according to offi cial

statistics of the U.S government.

Surveys of Canada are daunting for several reasons

Canada has a total area of approximately 3,855,000 miles 2

(10,000,000 km 2 ), making it the second largest country

in the world behind Russia About 10 percent of Canada’s surface area is freshwater With 150,000 miles (240,000 km) of shoreline, Canada has more shoreline than any other country in the world The climate in most of the northern portion of the country is cold, harsh, and challenging.

As part of Canada’s Earth Sciences Sector, GSC will continue to aid the development of the country’s rich natu- ral resources as well as conduct other geological projects

In addition to observing the position of the north magnetic pole, GSC research includes environmental studies, monitor- ing hazards such as earthquakes and landslides, and glaci- ology (the study of ice and glaciers) For example, much of the northern areas of the country consists of permafrost, defined as soil or rock that is frozen for much of the year

Permafrost thickness depends on the properties of the soil and its vegetation, along with local temperature and climate

The study of permafrost, along with other geological tures that are sensitive to the climate, will contribute to the ongoing worldwide research efforts to study global climate change.

fea-Origin and Variability of earth’s Magnetic Field

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If Earth was a huge bar magnet, the south magnetic pole might be expected at a location exactly opposite the north magnetic pole—the

ing ancient rocks Although the age of a rock is sometimes difficult to de-Trans-Antarctic Mountains in Antarctica (Ardo X Meyer/NOAA)

Aurora was the Roman goddess of dawn, and the term

bore-al derives from a Latin word referring to the north Because

the northern lights often appear as if a sun was rising in the

north, the phenomenon is called aurora borealis The term

for the southern lights is aurora australis, australis being

Latin for southern.

Northern and southern lights occur most often in polar regions, within about 1,500 miles (2,400 km) of the mag-

netic pole The displays usually last for only a few minutes

(though some endure for hours), can be as bright as

moon-light, and exhibit colors, most commonly green but also red,

violet, and blue In ancient times, people who lived in extreme

northern latitudes explained the strange displays with myths

and legends Some legends in Finland ascribe the lights to a

fable involving a fi ery arctic fox, which accounts for the Finnish

name for the northern lights, revontulet, meaning fox fi res

Other peoples, including Vikings, considered the lights to be

ghostly maidens.

The scientifi c cause of the northern and southern lights involves the magnetosphere, as suggested by the proximity

of the light displays to the magnetic poles Charged particles

of the solar wind become accelerated as they interact with

the magnetosphere These interactions are complicated and

not fully understood, but the result is an impulse directing

charges such as electrons speeding along the magnetic fi eld

lines, which converge at the magnetic poles (see fi gure on

page 38) Violent collisions between these charged particles

and oxygen or nitrogen in the atmosphere cause the

“magnetic storm” started fires, disrupted telegraphic nications, and produced light displays that were observed even

commu-in tropical areas such as Cuba and Hawaii.

Aurora borealis in Anchorage, Alaska, in 1977 (Yohsuke Kamide,

Na-goya University/Collection of Herbert Kroehl/NGDC, NOAA, NWS)

Origin and Variability of earth’s Magnetic Field

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Magnetic forces acting on electric charges are important for Earth because of the presence of charged particles in space and in the upper

Mapping the magnetosphere requires venturing into space Satel-magnetic field in space, giving geologists a bird’s-eye view To make an

Magnetometer used to measure magnetic fields in three

dimensions—note the instrument’s three axes (NASA/CETP)

Origin and Variability of earth’s Magnetic Field

and a liquid outer portion of iron along with nickel and a few lighter el-ements Although the core’s high temperatures preclude ferromagnetic

properties, the heat creates currents in the liquid outer core These cur-rents are often called convection curproperties, the heat creates currents in the liquid outer core These cur-rents because they involve a heat

transfer mechanism known as convection, in which the movement of

Origin and Variability of earth’s Magnetic Field

Mariner 2, which flew past Venus in 1962, have failed to detect a magnetic

field coming from the planet—Venus is not very magnetic, if at all

plication of the dynamo theory to planetary magnetic fields, yet there

Mars’s orbit is about 45 million miles (72 million km) farther than