Glossary :: A

Aa

A solidified lava flow with a blocky surface, formed from a viscous lava. The name is of Hawaiian origin.

Absolute age

An age of a rock or formation given in years determined by radiometric means. See also Relative age.

Adaptations

Traits that increase the fitness of an individual relative to individuals that lack the traits.

Agpaitic

Alkaline rocks having the alkalis over Al ratio in excess of 1, and containing a suite of complex alkali titano-, niobo- and zirconosilicates (e.g., eudialyte).

Alkalis

When applied to igneous rocks, this word implies the presence of Sodium (Na) and/or Potassium (K).

Allopatric

Where a population or species occupies a different geographic region to another population or species. See also sympatric and parapatric.

Allopatric speciation

Where different populations are formed, without intermediates, if physical barriers restrict gene flow. There are two types: vicariant speciation and peripatric speciation....More

Allopolyploidy

Chromosomes donated from >1 parental species. See also polyploidy and autopolyploidy.

Amethyst

Variant of quartz, purple in colour.

Anagenesis

The process by which evolutionary change along a single lineage creates a new species without any splitting of the phylogenetic tree (see cladogenesis).

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