BISC 120 - Lecture 12: Molecular Clock, Origin of Life, Fossils & Dating

Vocabulary practice flashcards covering molecular clocks, the abiotic origin of life, early Earth conditions, paleontology, fossil dating methods, and extinction patterns.

Molecular clock

A method using molecular differences and fossil evidence to estimate when lineages diverged.

Molecular-clock mutation rate

The characteristic whereby some genome regions accumulate mutations at relatively steady rates, although different regions evolve at different speeds.

Molecular-clock calibration

Using fossil dates or known mutation accumulation to estimate the rate of molecular change.

Pan-Homo divergence

The human-chimpanzee lineage split, estimated at about $6\text{--}8\text{ million years ago}$.

Age of Earth

About $4.5\text{ billion years}$.

Earliest prokaryotes

The earliest known cellular organisms, present by at least about $3.5\text{ billion years ago}$.

Hadean Earth

The period of early Earth about $4.5\text{--}4\text{ billion years ago}$, characterized by intense volcanism and meteor impacts.

Early atmosphere

Early-Earth atmosphere that had little to no oxygen and included water, nitrogen, $CO_2$, ammonia, and hydrogen.

Primitive soup hypothesis

The hypothesis that early oceans may have contained simple organic molecules produced abiotically.

Stanley Miller / Miller-Urey experiment

An experiment testing whether organic molecules could form under hypothetical early-Earth conditions.

Miller-Urey result

The finding that simple starting compounds produced organic monomers, including amino acids.

Importance of Miller-Urey

Showed that organic molecules can form abiotically under plausible early-Earth conditions.

Deep-sea vent hypothesis

The hypothesis that heat and pH gradients at alkaline vents may have powered the formation of organic molecules.

Volcanic clay hypothesis

The hypothesis proposing that clay surfaces and energy may have helped polymerize molecules such as RNA.

Polymerization

Joining smaller monomers together to form larger polymers.

Vesicle

A membrane-like structure that can form spontaneously from lipids in water.

Protocell

A simple membrane-bound structure that may have preceded true cells.

Ribozyme

An RNA molecule capable of catalyzing chemical reactions.

Self-replicating RNA

RNA capable of copying itself, potentially allowing early natural selection.

Early natural selection

The evolutionary process where more effective self-replicating RNA would increase in frequency relative to less effective copies.

Paleontology

The scientific study of fossil organisms.

Trace fossil

Indirect fossil evidence of an organism's activity.

Coprolite

Fossilized feces.

Relative dating

A dating method that determines whether rocks or fossils are older or younger relative to one another.

Principle of Superposition

A geological principle stating that in sedimentary layers, lower layers are older than layers above them.

Absolute dating

A dating method that determines an approximate numerical age of a rock or fossil.

Radiometric dating

A method that uses radioactive isotope decay and known half-lives to estimate age.

Half-life

The time required for half of a radioactive isotope to decay.

Argon-Argon dating

A radiometric method often used on volcanic rock with a half-life of about $1.25\text{ billion years}$.

Carbon-14 dating

A radiometric dating method using radioactive carbon-14.

Carbon-14 half-life

The half-life of carbon-14, which is about $5{,}730\text{ years}$.

Background extinction

The normal slow rate of extinction, accounting for about $96\%$ of extinctions.

Mass extinction

A rapid, global extinction affecting a broad range of species.