Geophysics

Earth's magnetic field, gravity, seismic tomography, and geothermal heat flow

What is geophysics?

Geophysics applies the tools and principles of physics — gravity, magnetism, seismic waves, and heat flow — to study Earth's structure and physical processes, from its deep interior all the way out to its surrounding magnetic field.

Earth's magnetic field

Earth generates its own magnetic field, produced by the movement of molten iron deep within its liquid outer core (introduced in the Geology article's discussion of seismic waves). This field extends far out into space, forming a protective shield called the magnetosphere that deflects much of the charged particle radiation streaming from the Sun, protecting both the atmosphere and life on the surface.

Gravity as a measurement tool

Earth's gravity isn't perfectly uniform everywhere on the surface — it varies slightly depending on the density of rock beneath a given location, and on latitude and elevation. By carefully measuring these small local variations in gravity, geophysicists can infer what kind of rock or structure lies underground without needing to drill or dig, since denser material (like certain ore deposits) produces a slightly stronger local gravitational pull than less dense surrounding rock.

Earthquakes and Earth's interior

Geophysics also studies earthquakes and the seismic waves they produce (introduced in the Geology article), using them not only to understand the earthquakes themselves but as a tool for imaging Earth's deep interior structure — since how these waves travel and bend as they pass through different materials reveals what those materials are and where their boundaries lie, even thousands of kilometers below the surface.

Why geophysics matters

Geophysics guides the search for oil, gas, minerals, and groundwater without costly, uncertain drilling; supports earthquake and volcanic hazard assessment to protect lives and infrastructure; and provides the physical tools needed to study Earth's deep interior, which can never be directly observed or sampled.