Earth History and Geological Time Scales

A comprehensive set of vocabulary flashcards covering Earth's geological timeline, major eons, eras, periods, and evolutionary milestones from the Big Bang to the present.

13.8 BYA

Formation of the Observable Universe starting with the Big Bang, where space, time, and the first simple elements like hydrogen and helium came into existence.

4.6 BYA

The Sun and Solar System form from a collapsing cloud of gas and dust, creating a rotating disk that coalesces into planets, moons, asteroids, and comets.

4.5 BYA

Earth forms from material in the young solar nebula; a giant impact likely produces the Moon and tilts Earth's axis while Zircon crystals begin to solidify.

Precambrian

A major span of time (4.5 BYA - 540 MYA) consisting of the Hadean, Archaean, and Proterozoic Eons, accounting for 88% of Earth's history.

Hadean Eon

The eon from 4.5-3.8 BYA characterized by the initial formation of Earth and its molten state due to impacts and radioactivity.

Archaean Eon

The eon from 3.8-2.5 BYA when Earth's crust cooled and solidified, liquid water oceans stabilized, and the first prokaryotic life appeared.

Proterozoic Eon

The eon from 2.5 BYA-540 MYA featuring the Great Oxygenation Event, the evolution of eukaryotic cells, and the first multicellular organisms.

Great Oxygenation Event

Occurred 2.5 BYA when oxygen-producing cyanobacteria raised O₂ levels, causing a crisis for anaerobes and enabling aerobic respiration.

Eukaryotic Cells

Cells with nuclei and mitochondria that evolved 2.0 BYA, likely through endosymbiosis between an archaeal host and a bacterium.

Ediacaran Period

The period from 630-540 MYA following Snowball Earth that features early macroscopic multicellular life, including soft-bodied animals and marine algae.

Phanerozoic Eon

The eon from 540 MYA to the present, encompassing the Paleozoic, Mesozoic, and Cenozoic Eras.

Cambrian Explosion

A rapid diversification 540-480 MYA where the basis of most modern animal body plans and main animal phyla appeared in the oceans.

Ordovician Period

The period from 480-440 MYA characterized by the diversification of marine invertebrates and the first simple land plants colonizing shorelines.

Silurian Period

The period from 440-420 MYA when the first vascular plants evolved, supported by mycorrhizal fungi, and jawed fishes became common.

Devonian Period

Known as the "Age of Fishes" (420-350 MYA), featuring the radiation of jawed fishes and the first tetrapods stepping onto land.

Carboniferous Period

Known as the "Age of Amphibians" (350-300 MYA), characterized by vast swamp forests and the accumulation of organic matter that formed coal deposits.

Permian Period

The period from 300-250 MYA when Pangaea formed and gymnosperms expanded; it ended with the worst mass extinction in post-Cambrian history.

End-Permian Extinction

Occurring 250 MYA, it is the worst mass extinction in history, marking the end of the Paleozoic Era.

Mesozoic Era

Known as the "Age of Reptiles" (250-65 MYA), containing the Triassic, Jurassic, and Cretaceous periods.

Triassic Period

The period from 250-200 MYA when early dinosaurs and mammals appeared as Pangaea began to rift.

Jurassic Period

The period from 200-150 MYA where non-avian dinosaurs were dominant and the first birds evolved from small theropod dinosaurs.

Cretaceous Period

The period from 150-65 MYA when flowering plants (angiosperms) appeared and non-avian dinosaurs remained dominant until their extinction.

Cretaceous-Paleogene (K-Pg) Extinction

An extinction event 65 MYA that eliminated non-avian dinosaurs and marked the start of the Cenozoic Era.

Cenozoic Era

Known as the "Age of Mammals" (65 MYA-Present), characterized by the rise of mammals, birds, and dominant angiosperms.

Paleogene Period

The "Early Tertiary" (65-25 MYA) including the Paleocene, Eocene, and Oligocene epochs, where mammals and birds rapidly diversified.

Neogene Period

The "Late Tertiary" (25-2.5 MYA) including the Miocene and Pliocene epochs, featuring the expansion of grasslands and the appearance of early hominins.

Quaternary Period

The period from 2.5 MYA to the present, encompassing the Pleistocene and Holocene epochs.

Pleistocene Epoch

Known for "The Last Ice Ages" (2.5 MYA-12,000 YA), during which the genus Homo evolved and dispersed globally.

Holocene Epoch

The current epoch starting 12,000 YA, characterized by stable climate, development of agriculture, and human-driven ecological change.