Geological and biological processes

Earth has evolved through geological and biological processes that have left traces of the original conditions. The outer surface is divided into several gradually migrating tectonic plates. The interior remains active, with a thick layer of plastic mantle and an iron-filled core that generates a magnetic field.

Aerial photography
When landmasses collide, rock layers can break. Geologists call these breaks ‘faults’ – photo: USGS

Gradually migrating tectonic plates

Earth has evolved through geological and biological processes that have left traces of the original conditions. The outer surface is divided into several gradually migrating tectonic plates. The interior remains active, with a thick layer of plastic mantle and an iron-filled core that generates a magnetic field. This iron core is composed of a solid inner phase, and a fluid outer phase. Convective motion in the core generates electric currents through dynamo action, and these, in turn, generate the geomagnetic field.

The solid and liquid matter

Geology is the science and study of the solid and liquid matter that constitutes the earth. The field of geology encompasses the study of the composition, structure, physical properties, dynamics, and history of Earth materials, and the processes by which they are formed, moved, and changed.

A major academic discipline

The field is a major academic discipline, and is also important for mineral and hydrocarbon extraction, knowledge about and mitigation of natural hazards, some Geotechnical engineering fields, and understanding past climates and environments.

Sedimentary rock

Rock units are first emplaced either by deposition onto the surface or intrude into the overlying rock. Deposition can occur when sediments settle onto the surface of the Earth and later lithify into sedimentary rock, or when as volcanic material such as volcanic ash or lava flows, blanket the surface. Igneous intrusions such as batholiths, laccoliths, dikes, and sills, push upwards into the overlying rock, and crystallize as they intrude.

Batholiths

A batholith is a large mass of intrusive igneous rock, also called plutonic rock, larger than 100 square kilometres in area, that forms from cooled magma deep in the Earth’s crust.

Laccoliths

A laccolith is a sheet-like intrusion that has been injected within or between layers of sedimentary rock, when the host rock is volcanic, the laccolith is referred to as a cryptodome.

Dikes

A dike is a sheet of rock that is formed in a fracture of a pre-existing rock body. Dikes can be either magmatic or edimentary in origin.

Sills

A sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or along the direction of foliation in metamorphic rock.

After the initial sequence of rocks has been deposited, the rock units can be deformed and/or metamorphosed. Deformation typically occurs as a result of horizontal shortening, horizontal extension, or side-to-side (strike-slip) motion. These structural regimes broadly relate to convergent boundaries, divergent boundaries, and transform boundaries, respectively, between tectonic plates.

Aerial photography
Himalaya Mountains – photo: USGS

Formed over hundreds of millions of years

Earth is estimated to have formed 4.54 billion years ago from the solar nebula, along with the Sun and other planets. Continents formed, then broke up and reformed as the surface of Earth reshaped over hundreds of millions of years, occasionally combining to make a supercontinent. Roughly 750 million years ago, the earliest known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia which broke apart about 540 million years ago, then finally Pangaea, which broke apart about 180 million years ago.


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Jane Roe

Jane Roe

Jane is a 24-year-old researcher who enjoys charity work, cycling and cookery. She is allergic to artificial food colourings. She has a severe phobia of sharks, and is obsessed with milkshakes.

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