- 4484
- EARTH'S MAGNETIC
FIELD - what caused it? -
The image of an atom, with electrons swarming around a central nucleus
bulging with protons and neutrons, is as iconic in our perception of
science. Exploring the fundamental
forces that govern our world, posing questions along the way that seek to
explain how the delicate balance of positive and negative charges paved the way
for gravity to shape our universe.
--------------- 4484 - EARTH'S MAGNETIC FIELD - what caused it?
- Magnetism is a manifestation of
electricity, and vice versa. Electricity and magnetism were imprinted into our
surroundings from the beginning. Five billion years ago when the new-born Earth
was a hot plasma of swirling electrical currents, these flows created magnetic
fields. As the magma cooled to form what is today the world's solid outer
crust, magnetism was locked into minerals containing iron, such as magnetite.
-
- Today, the Earth's liquid core is still a
frenzy of electric currents, which generate a magnetic field. This extends into
the atmosphere and far beyond, invisible to our normal senses. It first permeates the Earth's crust. This
is where it leaves a tangible imprint, evidence that there exists a force more
powerful than gravity at work within the Earth whose influence extends very
far.
-
- Way back in the earliest “Precambrian”,
four billion years ago, as the surface cooled, atomic elements accumulated in
the strata. The most stable of these, iron, is today one of the most abundant
elements in the crust.
-
- Igneous rocks formed from volcanic lava.
These rocks have the property that in the presence of a magnetic field, their
atoms of iron act like soldiers on parade as they themselves become magnetic.
This is exploited in popular demonstrations where the magnetic field of a bar
magnet can be made visible. A magnet
surrounded by iron filings
-
- A bar magnet induces magnetism in pieces of
iron, revealing the presence of its magnetic field spreading from one pole to
the other. Small filings of iron are first scattered on the surface of a table
and then a magnet is placed carefully among them. Its magnetic field induces
magnetism in the iron filings, turning them into thousands of miniature
magnets. Each of these duly orients itself in the magnetic field, revealing how
the direction of the magnetic force varies from place to place.
-
- Why do magnets have north and south
poles? The bar magnet is a simple model
illustrating what happens for the magnetic Earth itself. Earth's north and
south magnetic poles are analogous to those of the bar magnet, our planet's
magnetic field extending far into space.
-
- There are no iron filings out in space, but
there are large amounts of iron ores in the hills, cliffs, and mountains on
Earth. In some places, by chance, these magnetic clusters are quite extensive,
as on the Isle of Elba and Mount Ida in Asia Minor, where large outcrops retain
the magnetic imprint in rocks known historically as “lodestone”, now named
“magnetite”.
-
- There are legends how thousands of years ago
in ancient Greece, a shepherd wearing leather shoes held in place by iron nails
stumbled across magnetite when the powerful magnetism gripped the nails in his
footwear. Whether or not a shepherd named Magnes discovered the eponymous rock,
and if so whether it was in Magnesia, north of Athens, or on Mount Ida in Asia
Minor, or even another Mount Ida in Crete, it is very likely had such
experiences.
-
- Certainly, the power of magnetism would
have been apparent ever since the Iron Age. Lightning is a flash of electric
current which generates intense magnetic fields and magnetizes ferrous rocks.
Smelting to retrieve the pure iron metal from these sources would have revealed
their magnetic attraction.
-
- So, the phenomenon has probably been known
for some 3,000 years. Like the discovery of fire, that of magnetism probably
arose in several places independently, all inspired by the natural
magnetization of iron in rocks.
-
- For magnetic rocks are ubiquitous. By the
sixteenth century travelers recorded the best examples, from East India and the
Chinese coast: Very massive and
weighty, the stone will draw or lift up the just weight of itself in iron or
steel.
-
-
May 27, 2024 EARTH'S
MAGNETIC FIELD - what
caused it? 4484
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--------------------- --- Monday, May 27, 2024
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