DEFINITION OF SUPERCONTINENT CYCLE

Semi-regular grouping of the planet’s

landmasses into single or large continents that remain stable

for a period of time, then disperse, and eventually come back

together as new amalgamated landmasses with a different distribution.

At several times in Earth history, the continents

have joined together forming one large supercontinent, with

the last supercontinent Pangea (meaning all land) breaking up

approximately 160 million years ago. This process of supercontinent

formation and dispersal and re-amalgamation seems

to be grossly cyclic, perhaps reflecting mantle convection patterns

but also influencing climate and biological evolution.

Early workers noted global “peaks” in age distributions of

igneous and metamorphic rocks and suggested that these represent

global orogenic or mountain building episodes, related

to supercontinent amalgamation.

The basic idea of the supercontinent cycle is that continents

drift about on the surface until they all collide, stay

together, and come to rest relative to the mantle in a place

where the gravitational potential surface (geoid) has a global

low. The continents are only one-half as efficient at conducting

heat as oceans, so after the continents are joined together,

heat accumulates at their base, causing doming and breakup

of the continent. For small continents, heat can flow sideways

and not heat up the base of the plate, but for large continents

the lateral distance is too great for the heat to be transported

sideways. The heat rising from within the Earth therefore

breaks up the supercontinent after a heating period of several

tens or hundreds of millions of years, the heat then disperses

and is transferred to the ocean/atmosphere system, and continents

move away until they come back together forming a

new supercontinent.

The supercontinent cycle has many effects that greatly

affect other Earth systems. First, the breakup of continents

causes sudden bursts of heat release, associated with periods

of increased, intense magmatism. It also explains some of the

large-scale sea-level changes, episodes of rapid and

widespread orogenesis, episodes of glaciation, and many of

the changes in life on Earth.

Compilations of Precambrian isotopic ages of metamorphism

and tectonic activity suggest that the Earth experiences

a periodicity of global orogenesis of 400 million years. Peaks

have been noted at time periods including 3.5, 3.1, 2.9, 2.6,

2.1, 1.8, 1.6, and 1.1 billion years ago, as well as at 650 and

250 million years ago. One hundred million years after these

periods of convergent tectonism and metamorphism, rifting is

common and widespread. A. H. Sutton (1963) proposed the

term chelogenic cycle, in which continents assemble and

desegregate in antipodal supercontinents.

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