Time scales and Origin of life — Vocabulary Flashcards

Vocabulary-style flashcards covering Earth's time scales, major geologic eras, key fossil evidence, and origin-of-life concepts as presented in the lecture notes.

Precambrian supereon

The earliest major division of Earth's history, from about 4.6 billion years ago to 543 million years ago.

Paleozoic era

Time period (543 MYA – 250 MYA) when life moved onto land; ends with the Permian extinction; includes early land plants and animals.

Mesozoic era

Time period (250 MYA – 65 MYA) known as the Age of Reptiles; ends with the K–T extinction; first mammals appear during this era.

Cenozoic era

Time period (65 MYA – present) known as the Age of Mammals; Earth has undergone significant changes through this era.

Holocene epoch

The current epoch within the Quaternary; described as too small to fit on a simple geological scale.

Hadean eon

The earliest eon in Earth's history, often depicted as a molten, minerals-rich stage before life.

Late Hadean eon

The later part of the Hadean eon, preceding the Archean; context for the origin of life in notes.

First life

Origin of life on Earth, occurring between about 4.2 and 3.8 billion years ago (BYA).

Stromatolites

Layered sedimentary formations created by microbial mats; fossil evidence of early life; modern stromatolites exist in Australia.

Multicellular life (late Precambrian)

Appearance of multicellular organisms around 1 BYA, later in the Precambrian.

Trace fossil

A fossil that records the activity of an organism (evidence of movement or behavior) rather than the organism itself.

Trilobite fossil

Fossils from the Paleozoic era; notable for features such as intact eyestalks in some specimens.

Archaeocyathids

Cambrian sponge-like animals; early reef-builders during the Cambrian.

Cambrian explosion

Rapid diversification of life at the start of the Paleozoic; not a literal big bang, evidenced by fossils like Burgess Shale.

Burgess Shale

Famous Cambrian fossil site with exceptional preservation of early soft-bodied organisms.

First land plants and animals

Origin of life on land during the Paleozoic; evidence includes carpet moss and early amphibians (tetrapods).

Permian extinction

Major extinction event at the end of the Paleozoic era, terminating much of its biodiversity.

Morganucodon watsoni

Early mammal from the Mesozoic, appearing around 205 MYA.

K–T extinction

Cretaceous–Paleogene extinction event (~65 MYA) marking the end of the Mesozoic, associated with a large impact.

KT boundary

Geologic boundary layer corresponding to the K–T extinction event.

Cenozoic era — age of mammals

Era from ~65 MYA to present; diversification and dominance of mammals.

Panspermia

Hypothesis that life originated elsewhere and was delivered to Earth via celestial bodies.

Abiotic synthesis of organic materials

Non-biological formation of organic molecules such as amino acids, nucleotides, sugars, lipids, and ATP.

Formation of polymers

Polymerization of organic molecules; clay surfaces rich in Fe and Zn can promote proximity and assembly.

Formation of protobionts

Development of protocell-like structures (liposomes) that encapsulate organic materials.

Origin of hereditary material

Emergence of genetic material that can store and transmit information (leading to RNA world).

RNA world

Hypothesis that early life used RNA for both information storage and catalysis, preceding DNA–protein systems.

Four characteristics of RNA (in RNA world)

RNA easily forms abiotically, can replicate, carries hereditary information, and has catalytic properties.

Viroids

Small, circular RNA molecules; potential clues to the RNA world hypothesis.

DNA and RNA in life today

All current life forms use both DNA and RNA for genetic information and function.

Earth’s early environment (3.8 BYA)

Molten rock, no free oxygen (reducing atmosphere), and high-energy conditions that may have enabled Abiogenesis.

3.8 BYA diversification start

The emergence of life around 3.8 BYA led to the later biological diversity of Earth (supported by Hug et al., 2016).