|How does the composition and phases of earth's
inner layers generate a magnetic field?|
|Question Date: 2018-02-21|
DoMaria, our Earth is composed of three
layers. A solid, hot, inner core, a liquid
mantle made of iron, nickel, and other metals, and
the earths crust.
The mantle is constantly moving and flowing
around because of convection currents. That
means that the colder more dense metal sinks to
the bottom while the hot stuff rises to the top.
That movement of liquid iron creates electric
currents, and those electric currents
induce magnetic fields. Separate magnetic
fields are all aligned in similar directions,
which causes them to combine and produce one,
giant magnetic field around the planet!
The Earth's core is made mostly of an
iron-nickel alloy, with a minor component of
lighter elements like carbon and sulphur. Due to
the extremely high pressures that occur at the
center of the Earth, the inner core is
solid. However, the outer core is liquid
because the pressures are lower towards the
surface of the Earth. In terms of chemical
composition, both regions of the core are similar,
As heat escapes from the inner core towards the
core-mantle boundary, it generates
convection in the liquid outer core around it.
This process is similar to a lava lamp: hot,
buoyant liquid core material rises, whereas
colder, denser core material sinks, leading to the
movement of the material in the liquid outer core.
The liquid core material is electrically
conductive, so its movement (along with the
rotation of the planet) induces a magnetic
field. This is called the dynamo
process, and the same process is
responsible for generating magnetic fields
associated with other planetary bodies in the
As of yet, no one has made a trip to the center
of Earth, but scientists use seismic waves to
understand the physical and compositional layers
that make up Earth. Using seismic waves, our
understanding is that Earth has a dense, solid
inner core composed primarily of iron. Earth's
core would be about two-thirds the size of the
moon, about as hot as the surface of the sun, and
at a pressure so high the iron is forced into a
solid state that cannot melt.
Surrounding the inner core is a liquid
outer core. The pressure is slightly less,
enabling the liquid state at those very high
temperatures. And it is made up of mostly
iron, but also likely contains small
quantities of lighter metals like nickel.
Earth's magnetic field relies on this liquid
outer core. Differences in temperature and
pressure within the outer core enable
convection currents to form as slightly
colder and denser materials sink and attach to the
inner core while hotter and lighter materials are
buoyantly driven upward. Earth's rotational
spin on its axis also creates something called the
Coriolis effect, which further causes convection.
As the outer core convects, or swirls
around, the liquid iron creates electric
currents that generate magnetic fields. The
Coriolis effect, due to Earth's spinning, causes
the magnetic fields to align parallel to
Earth's axis. All of these combined generate
the appropriate flow pattern and all the currents
accumulate and become a large magnetic field
The actual math calculations required to
understand how this all works is quite complex,
but the main factors require a conducting fluid
(liquid outer core made of iron) and sufficient
energy to convect the fluid quickly and in the
appropriate flow pattern.
Good question. The Earth's outer core is made
of a molten mixture of iron and nickel, and, like
the rest of the Earth, it rotates. This
creates an electric current that also flows
around the Earth. I am not sure how the rotation
creates this electric current; hopefully a
geophysicist will answer this question and explain
An electric current creates a magnetic
field because electricity and magnetism are
the same force.
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