Week 9 Vocab: Stratigraphy and Geologic Time

Principle of Superposition

Chronological organisation of rock layers; the oldest rocks are at the bottom, and the layers

become increasingly younger towards the top.

Stratigraphy

The science of using the arrangement and composition of rock layers to interpret geological history.

A formation

A large, uninterrupted sequence of rock that is made of multiple layers that all share similar properties, and that all formed under similar conditions.

Radiometric Dating

The use of isotopic ratios to calculate age of a rock.

Radioactive Isotopes

Variations of an element that differ in the number of neutrons; has a specific half-life or rate of decay

The geologic time scale

A standardised series of chronological divisions that parses the Earth's history into discrete named units.

Stratigraphic Column

Geologic diagram that illustrates a sequence of rock layers, with the oldest at the bottom and the youngest at the top; often illustrates the thicknesses of each layer.

The Cambrian Explosion

Dramatic diversification of aquatic animal life

that occurred approximately 541 million years ago.

Trilobites

Extinct group of marine arthropods; first evolved during the Cambrian and died out at the End-Permian Mass Extinction.

Pterosaurs

Group of flying archosaurs closely related to dinosaurs; lived during the Late Triassic to the Cretaceous; the first group of vertebrates to evolve flight; examples: Quetzalcoatlus,

Rhamphorhynchus.

Plesiosaurs

A group of diapsids specially adapted to a marine life; lived during the Early Jurassic to Late Cretaceous; examples: Dolichorhynchops, Elasmosaurus, Kronosaurus

Pikaia

Thought to be one of the oldest known animals with a notochord; lived during the Cambrian.

Permo-Triassic Mass Extinction

The single largest mass extinction event in Earth history; occurred 252 million years ago and wiped out an estimated 96% of all marine life and 70% of all terrestrial life.

Pangaea

Supercontinent, comprised of all the Earth's major

landmasses, that formed around 300 million years ago and began breaking up around 200 million years ago.

Mosasaurs

A group of extinct lepidosaurs, related to modern snakes and monitior lizards, that were highly adapted to a marine life; evolved in the Late Cretaceous.

Ammonite

A kind of extinct marine cephalopod with a spiral shell; thrived from the Devonian through the

Cretaceous but died out during the End-Cretaceous Extinction.

The Burgess Shale

Fossil rich deposit in British Columbia, Canada; famous for its exceptional preservation of 505 million years old marine organisms

Isotope Ratio

The ratio of a naturally occurring radioactive isotope and its decay products

Ichthyosaurs

A group of marine reptiles that first evolved in the Triassic and went extinct towards the end of the Cretaceous. They look similar to dolphins, due to convergent evolution of body types. Name literally means: "fish lizard," even though they aren't fish or lizards!

Rhamphorhynchoids

Early group of flying reptiles, which were common in the Late Triassic and throughout the Jurassic. Typically had long tails compared to later flying reptiles

Pterodactyloids

Flying reptiles that differed to early relatives in morphology of their tails, which were short, and the carpels in their wrists, which were elongated and made a greater contribution to the length of the wing. Often had large head crests.