Earth systems and geophysics

Earth's inner core

Earth's inner core is the solid, centralmost sphere of the planet, made mostly of an iron-nickel alloy, bounded by the liquid outer core at about 1,221 km.

Earth's mantle

Earth's mantle is the thick, mostly solid rock layer between the crust and the core, making up most of Earth's mass and driving plate tectonics and volcanism.

Earth's outer core

Earth's outer core is the liquid iron-nickel alloy shell surrounding the solid inner core, between about 2,890 and 5,150 km deep, whose churning metal generates Earth's magnetic field.

Earthquake early warning

Earthquake early warning (EEW) detects an earthquake that has already begun and sends alerts giving people seconds to tens of seconds to take protective action before strong shaking arrives.

Earthquake location is the seismological procedure that determines where and when an earthquake started, solving for the hypocenter's coordinates and origin time from arrival times recorded at many stations.

Earthquake swarm

An earthquake swarm, also called a seismic swarm, is a sequence of earthquakes clustered in a small area with no dominant mainshock, often tied to volcanic or geothermal activity.

Earthquake swarms

An earthquake swarm is a sequence of many similar, mostly small earthquakes clustered in space and time without a mainshock, often driven by fluids or magma.

Earthquake tomography

Earthquake tomography, or local earthquake tomography, is a seismological imaging method that uses earthquake wave travel times to map three-dimensional velocity structure of Earth's interior.

Electrical resistivity imaging

Electrical resistivity imaging, also called electrical resistivity tomography (ERT), is a geophysical method that maps subsurface resistivity by injecting current and measuring voltage, used to find groundwater, contaminants, and geology.

Electrical resistivity method

The electrical resistivity method is a geophysical surveying technique, originating in the 1910s, that injects current into the ground to map groundwater, salinity, fractures, and contaminants.

Electrical resistivity tomography

Electrical resistivity tomography (ERT) is a geophysical imaging method that reconstructs subsurface electrical resistivity from electrode measurements, producing 2D sections and 3D volumes for hydrogeology, geotechnics, and environmental studies.

Electromagnetic tomography

Electromagnetic tomography is a geophysical method that reconstructs subsurface electrical conductivity from electromagnetic field measurements made at the surface, in boreholes, or from the air.

Entisols

Entisols are one of the 12 orders of USDA Soil Taxonomy: mineral soils with little or no horizon development, covering about 18 percent of Earth's ice-free land.

Environmental degradation

Environmental degradation, also called environmental damage or ecological degradation, is the deterioration of the natural environment through resource depletion, ecosystem destruction, and pollution, reducing the capacity of land, water, and air to sustain life.

Environmental hazard

An environmental hazard, also called an environmental health hazard, is a natural or human-made condition that can harm health, ecosystems, or property, with air pollution the deadliest.

Equator

The Equator is the imaginary line at 0 degrees latitude halfway between the poles, dividing Earth into two hemispheres and measuring about 40,075 km around.

Equivalent source method

The equivalent source method, also called equivalent sources, is a geophysical technique that fits fictitious sources to gravity or magnetic data for interpolation and continuation.

Erosion susceptibility mapping

Erosion susceptibility mapping is a geospatial modeling method that combines environmental factor layers with machine learning classifiers to classify land into erosion-proneness categories, supporting land-use planning and soil conservation.

Etalon (satellite)

Etalon is a pair of Russian passive geodetic satellites, Etalon-1 and Etalon-2, launched in 1989 with GLONASS satellites and covered in corner-cube retroreflectors for satellite laser ranging.

Euler deconvolution

Euler deconvolution is a semi-automatic method for interpreting magnetic and gravity survey data, estimating the location and depth of field sources by solving Euler's homogeneity equation over moving data windows.

Ferralsols

Ferralsols are deeply weathered, strongly leached soils of the humid tropics, defined by a ferralic horizon and corresponding closely to the Oxisols of USDA Soil Taxonomy.

Field spectroscopy

Field spectroscopy is the measurement of spectral reflectance of natural surfaces in the field using portable spectroradiometers, chiefly to support calibration and validation of satellite and airborne imagery.

Figure of the Earth

Figure of the Earth, also called the shape of the Earth, is the model geodesy uses for the planet's form: an oblate spheroid plus the geoid.

Flat Earth

Flat Earth, also known as the flat Earth theory, is the disproven belief that Earth is a plane rather than a sphere about 12,742 km across.

Fluvisols

Fluvisols are young soils formed in recent river, lake, and marine deposits in floodplains, deltas, and tidal marshes, classified by stratified sediment and irregular organic matter renewed by periodic flooding, covering about 350 million hectares.

Fluxgate magnetometer

A fluxgate magnetometer is a vector instrument measuring DC and low-frequency magnetic fields via a saturating ferromagnetic core, invented in 1936 and used from space missions to submarine detection.

Full-waveform inversion

Full-waveform inversion (FWI) is a seismic imaging method that iteratively adjusts a subsurface velocity model until simulated seismic waves match recorded survey data, waveform by waveform.

Future of Earth

The future of Earth covers the planet's projected evolution across billions of years: near-term warming, a supercontinent in 200 to 250 million years, and eventual destruction by the Sun.

Gall–Peters projection

The Gall–Peters projection, also known as the Peters projection, is a cylindrical equal-area map projection that preserves area exactly while distorting shapes, presented by James Gall in 1855.