Origin of Life & Earth’s Early History

Flashcards covering the geologic time scale, fossil dating methods, hypotheses on the origin of life, and major evolutionary milestones from the Earth's formation to the present.

Age of Earth

The Earth is approximately $4.6\,\text{billion years old}$.

Start of Life

Life on Earth began approximately $3.8\,\text{billion years ago}$.

Paleozoic

A term meaning "ancient life".

Mesozoic

A term meaning "middle life".

Cenozoic

A term meaning "recent life".

Paleontologist

A scientist who studies fossils to learn about ancient life, including structure, movement, diet, and past environments.

Permineralization

A fossilization process where minerals carried in water are deposited around a hard structure and may replace the hard structure itself.

Relative Dating

A method used to determine whether a fossil is older or younger than other fossils based on its location in the ground; it does not provide an absolute date in years.

Radiometric Dating (Absolute Dating)

A method that uses the proportion of radioactive isotopes to stable isotopes, such as $\text{Carbon-14}$ or $\text{Potassium-40}$, to calculate the specific age of a sample.

Index Fossil

Fossils of organisms that existed during short or specific spans of time over large geographic areas and are found abundantly; they help determine the age of rock layers (strata).

Miller & Urey Experiment, 1953

An experiment showing that mixtures of organic compounds necessary for life, such as amino acids and sugars, could have originated from simpler compounds in primitive Earth’s atmosphere.

Meteorite Hypothesis (Australia, 1969)

A proposal based on the discovery of organic molecules in space, suggesting that amino acids arrived on Earth via meteorites.

Iron-sulfide bubble hypothesis (1990s)

A hypothesis proposing that hot iron sulfide rising from the ocean floor formed chimney-like structures where the first bio-molecules may have combined.

Lipid membrane hypothesis

The proposal that lipids formed enclosed spheres called liposomes, which may have formed around organic molecules to act as early cell membranes.

RNA World Hypothesis

The proposal that RNA, rather than DNA, was the genetic material of early life on Earth.

Ribozymes

Diverse types of RNA that can catalyze reactions.

Archaea

Primitive bacteria that were the first life on the planet during the Archean Eon ($3.8\text{--}2.5\,\text{bya}$); they are anaerobic and chemosynthetic.

Cyanobacteria

Organisms that produced high levels of oxygen, which was first trapped by iron in rocks and eventually formed free oxygen for aerobic prokaryotes.

Stromatolites

Rock structures where the earliest fossilized cyanobacteria, dating to $3.5\,\text{bya}$, have been discovered.

Theory of Endosymbiosis

A theory proposing that mitochondria and chloroplasts were once individual bacteria ingested by another bacterium, eventually becoming symbiotic parts of a larger eukaryotic cell.

Cambrian explosion

The earliest part of the Paleozoic Era characterized by a great diversification of life, including the earliest vertebrates and marine invertebrates.

Mesozoic Era (Age of Reptiles)

The era from $251\text{--}65\,\text{mya}$ comprising the Triassic, Jurassic, and Cretaceous periods, characterized by dinosaurs and the rise of mammals.

Homo sapiens

The modern human species which appeared in the Quaternary Period about $200,000\,\text{years ago}$.