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, however.

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 universe.

Great question!

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 enveloping Earth.

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 it better.

An electric current creates a magnetic field because electricity and magnetism are the same force.