An earthing system connects specific parts of an electric power system with the ground, typically the Earth's conductive surface, for safety and functional purposes.

Earth's mantle is a layer of silicate rock between the crust and the outer core.

The flow of heat from Earth's interior to the surface comes from two main sources in roughly equal amounts: the radiogenic heat produced by the radioactive decay of isotopes in the mantle and crust, and the primordial heat left over from the formation of Earth.

If the incoming energy flux is not equal to the outgoing energy flux, net heat is added to or lost by the planet (if the incoming flux is larger or smaller than the outgoing respectively).

Earth's energy budget accounts for the balance between the energy that Earth receives from the Sun, and the energy the Earth radiates back into outer space after having been distributed throughout the five components of Earth's climate system.

Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume.

The atmosphere of Earth is the layer of gases, commonly known as air, retained by Earth's gravity, surrounding the planet Earthand forming its planetary atmosphere.

Earth science or geoscience includes all fields of natural science related to planet Earth.

E-procurement is the business-to-business or business-to-consumer or business-to-government purchase and sale of supplies, work, and services through the Internet.

A Dyson sphere is a hypothetical megastructure that completely encompasses a star and captures a large percentage of its power output.

The dyne is a derived unit of force specified in the centimetre–gram–second (CGS) system of units.

A dynamo is an electrical generator that creates direct current using a commutator.

Dynamic voltage restoration is a method of overcoming voltage sags and swells that occur in electrical power distribution.

A dynamic tidal power dam is a long barrier of 30 km or more which is built perpendicular to the coast, running straight out into the sea, without enclosing an area.

Dynamic tidal power is an untried but promising technology for tidal power generation.

Dynamic range is the ratio between the largest and smallest values that a certain quantity can assume.

Glass that can used to assist in the regulation of temperature and light within a building thereby reducing the energy requirements of the building and emissions.

A dye-sensitized solar cell is a low-cost solar cell belonging to the group of thin film solar cells.

Due Diligence is the close scrutiny and evaluation prior to a lease, purchase or sale; especially in respect of economic, legal, tax and financial circumstances.

Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire).