Earth Science - Chapter 1

Introduction to Geology and Plate Tectonics

Asthenosphere

mechanically weak, ductile subdivision of the mantle that underlies the atmosphere

Atmosphere

gaseous portion of a planet; the planet’s envelope of air. one of the traditional subdivisions of Earth’s physical environment

Catastrophism

the concept, created by Georges Cuvier, that Earth was shaped by catastrophic events of a short-term nature

Continental shelf

the submerged, gently sloping edge of a continent extending from the coastline to a drop-off point known as the shelf-break

Continental drift

a hypothesis, credited largely to Alfred Wegener, that suggested all present continents once existed as a single supercontinent. Further, beginning about 200 millin years ago, the supercontinent began breaking into smaller continents, which then drifted to their present position

Continental slope

the steep gradient that leads to the deep-ocean floor and marks the seaward edge of the continental shelf

Convection

the transfer of heat by the mass movement or circulation of a substance

Convergent plate boundary

a boundary in which two plates most together, resulting in oceanic lithosphere being thrust beneath an overriding plate, eventually to be reabsorbed into the mantle. it can also involve the collision of two continental plates create a mountain system

Core

the innermost layer of Earth based on composition. it is thought to be largely an iron-nickel alloy with minor amounts of oxygen, silicon, and sulphur

Crust

the very thin outermost layer of Earth

Divergent plate boundary

a boundary in which two plates move apart, resulting in upwelling of material from the mantle to create new sea floor

Geologist

a person who is trained in and workms in the geological sciences

Geology

the science that examines Earth, its form and composition, and the changes that it has undergone and is undergoing

Historical geology

a major division of geology that deals with the origin of Earth and its development through time, usually involves the study of fossils and their sequence in rock beds

Hydrosphere

the water portion of Earth; one of the traditional subdivisions of the physcial environment

Igneous rock

rock formed from the crystallization or solidification of magma or lava

Inner core

the solid innermost layer of Earth, about 1221 km in radius

Law of superposition

in any undefermed sequence of sedimentary rocks, each bed is older than the one above or younger than the one below

Lithosphere

the rigid outer layer of Earth, including the crust and uppermost mantle

Lower mantle/Mesosphere

the part of the mantle that extends from the core-mantle boundary to a depth of 660 km

Mantle

one of Earth’s compositional layers, the solid rocky extends from the base of the crust to a depth of 2900 km

Metamorphic rock

rock formed by the alteration of pre-existing rock deep within Earth (but still in a solid state) by heat, pressure, and/or chemically active fluids

Nebular theory

a model for the origin of the solar system that supposes a rotating nebula of dust and gases that contracted to form the Sun and planets

Outcrops

the bedrock exposed at the ground surface

Outer core

a layer beneath the mantle about 2250 km thick, which has the properties of a liquid

Pangaea

the proposed supercontinent about 200 million years ago began to break apart and form the present land masses

Paradigm

a theory that is held with a very high degree of confidence and is comprehensive in scope

Physical geology

a major division of geology that examines the materials of Earth and seeks to understand the processess and forces acting beneath on Earth’s surface

Plate tectonics

the theory that proposes that Earth’s outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself

Principle of fossil succession

fossil organisms succeed one another in definite and determinable order, and any time period can be reorganized by its fossil content

Relative dating

the placement of rocks and structures in their proper sequence or order, only the chronological order of events in determiend

Rock cycle

a model that illustrates the origin of the three basic rock types and the interralatedness of Earth materials and processes

Sea-floor spreading

the hypothesis first proposed in the 1960s by Harry Hess that suggested that new oceanic crust is produced at mid-ocean ridges, which are the sites by divergence

Sediment

a material that settles out in particular form from a fluid, either by gravitational factors or precipitation

Sedimentary rock

the rock formed from the weathered products of preexisting rocks that have been transported, deposited, and lithified

Shield

a large, relatively flat expanse of ancient metamorphic and igneous rocks within the stable continental interior

Subduction

the process by which oceanic lithospheric plunges into the mantle along the convergent

System

a group of interacting or interdependent parts that form a complex whole

Transform boundary

a boundary in which two plates slide part each other without creating or destroying the lithosphere

Trench

an elongate depression in the sea floor produced by bending of oceanic crust during subduction

Uniformitarianism

the concept that the processes that have shaped Earth in the geological part are essentially the same as those operating today