History of Life on Earth - Lecture Notes

Vocabulary-style flashcards covering the timeline, conditions, and major biological transitions in the history of life on Earth.

Age of Earth

Approximately $4.6$ billion years (BY) old, determined through radiometric dating of meteorites and moon rocks.

Early Atmosphere Composition

Early Earth's atmosphere contained $CO_2$, $CH_4$, $NH_3$, $H_2S$, and $H_2O$, with no free oxygen.

A. I. Oparin and J. B. S. Haldane

Scientists who independently hypothesized in the 1920s that the early atmosphere was a reducing environment rich in hydrogen, methane, and ammonia.

Miller and Urey Experiment

A 1953 laboratory experiment that demonstrated the abiotic synthesis of organic molecules in a reducing atmosphere was possible.

Murchison Meteorite

A meteorite from Australia containing more than $80$ amino acids, lipids, simple sugars, and nitrogenous bases, supporting an extraterrestrial origin of organic compounds.

Abiotic Synthesis of Polymers

The process where small organic molecules polymerize when concentrated on hot sand or clay.

Protobionts

Aggregates of abiotically produced molecules surrounded by a membrane; an essential step in the origin of life.

Liposomes

Structures that can form when lipids or other organic molecules are added to water.

Ribozymes

RNA molecules that can catalyze reactions, believed to be used by the earliest cells to store information.

Sedimentary Strata

Layers of rock that reveal the relative ages of fossils; deeper fossils are more ancient, while those near the surface are more recent.

Radiometric Dating

A method used to determine the absolute ages of fossils based on the decay of radioactive isotopes into daughter isotopes.

Half-life

The amount of time it takes for $50\%$ of a radioactive isotope to decay.

First Organisms

Prokaryotes (Bacteria and Archaea) that appeared about $3.5$ billion years ago; they were likely anaerobic heterotrophs or autotrophs.

Oxygen Revolution

The accumulation of oxygen in the atmosphere beginning $2.7$ BYA, resulting from oxygenic photosynthetic bacteria that evolved between $3.5$ and $2.7$ BYA.

Endosymbiotic Theory

The theory that mitochondria and plastids were formerly small prokaryotes that began living within larger host cells as undigested prey or internal parasites.

First Eukaryotes

Cells containing mitochondria and plastids that appear in the fossil record starting $2.1$ billion years ago.

Small Red Algae

The oldest fossils of multicellular eukaryotes, dating back to approximately $1.2$ billion years ago.

Ediacaran Biota

An assemblage of larger and more diverse soft-bodied organisms that lived from $635$ to $541$ million years ago.