Chapter 25 Exam Study Guide: General Biology II

Comprehensive vocabulary flashcards covering the origin of life, early Earth conditions, abiogenesis theories, fossil types, radiometric dating, and key milestones in the geological record based on Chapter 25.

Big Bang Theory

The prevailing cosmological model for the observable universe, describing how it expanded rapidly outward from a very high-density singularity and high-temperature state approximately $13.8\text{ billion}$ years ago.

Protoplanetary Accretion Disk

A flattened disk of gas, rocks, and debris orbiting the newly formed Sun $4.6\text{ billion}$ years ago, out of which planets, moons, and asteroids collided and fused to form our solar system.

Abiogenesis Hypothesis

The model proposing that life originated in four abiotic stages: (1) formation of small organic monomers like amino acids and nucleotides, (2) assembly of polymers like proteins and nucleic acids, (3) packaging into protocells with membranes, and (4) origin of self-replicating genetic molecules.

Oparin-Haldane Hypothesis

The independent proposal by Aleksandr Oparin (1924) and John Haldane (1929) that an oxygen-free, reducing early atmosphere powered by lightning or UV light could abiotically synthesize organic compounds, creating a "hot dilute soup" in the oceans.

Miller-Urey Experiment

A classic 1952 chemical experiment conducted by Stanley Miller and Harold Urey simulating early Earth conditions using $H_2O$, $CH_4$, $NH_3$, and $H_2$ with electric sparks, which produced well over 20 different amino acids abiotically.

Deep Sea Hydrothermal Vent Theory

A hypothesis proposing that life began at submarine thermal vents where hydrogen-rich fluids merged with carbon dioxide-rich ocean water, driving redox reactions to produce organic compounds.

Murchison Meteorite

A meteorite that landed in Australia in 1969 containing 14,000 molecular compounds, including 70 amino acids (such as glycine, alanine, isovaline, and pseudoleucine) and nitrogenous bases like uracil and xanthine, proving organic molecules can originate in space.

Proteinoids

Abiotically synthesized polypeptides produced by Sydney Fox by dripping organic amino acid monomers onto hot sand, rock, or clay to induce dehydration polymerization.

Montmorillonite Clay

A soft phyllosilicate mineral group that acts as a catalyst to help nucleotides assemble into RNA polymers and accelerates the self-assembly of fatty acids into membrane-bound vesicles.

Liposomes

Membrane-bound vesicles that auto-assemble when fatty acids are placed in water, forming simple lipid structures capable of encapsulating RNA and minerals.

Ribozymes

RNA molecules with enzymatic/catalytic properties—discovered by Thomas Cech and Sidney Altman—capable of self-splicing, replication, and peptide bond formation without proteins.

Fossil Record

The total collection of preserved remains, impressions, or traces of once-living organisms (such as bones, shells, exoskeletons, amber, tracks, and DNA remnants) archived in Earth's rock layers.

Strata

Superimposed layers of sedimentary rock formed from compressed mud and sand, where deeper layers represent older geological periods containing ancient fossils.

Mold Fossil

A type of fossil formed when an organism's hard body parts decay or dissolve in sediment, leaving behind a hollow cavity in the shape of the original structure.

Cast Fossil

A replica of an organism formed when minerals or sediment fill an empty mold cavity and harden into stone.

Trace Fossils

Preserved evidence of biological activity or behavior rather than body parts, including footprints, trackways, burrows, nests, toothmarks, gastroliths, and coprolites.

Resin-based Fossil

An organic true form fossil formed when an organism becomes trapped in tree sap/resin (such as secretions from Hymenaea courbaril) that hardens into amber over time.

Index Fossils

Fossils of organisms that were abundant, widespread, easily recognizable, short-lived, and resistant to decay, used to correlate and date the relative age of rock strata across the globe.

Radiometric Dating

An absolute dating method that calculates the age of rocks or fossils by measuring the ratio of a radioactive parent isotope to its daughter decay product based on its half-life.

Half-life

The time required for $50\text{\%}$ of a radioactive parent isotope to decay into a stable daughter isotope, a rate unaffected by temperature, pressure, or environment.

Uranium-Lead (U-Pb) Dating

A radiometric dating technique performed on zircon crystals that measure the decay of ${}^{238}\text{U}$ and ${}^{235}\text{U}$ into lead isotopes to date rock formations from $1\text{ million}$ to over $4.5\text{ billion}$ years old.

Geomagnetic Field Reversals

Periodic switches between Earth's magnetic north and magnetic south poles (chrons) recorded in iron-bearing rocks, which can be matched against the Geomagnetic Polarity Time Scale (GPTS) to date strata.

Geologic Record

A standard time scale dividing Earth's history into four eons (Hadean, Archaean, Proterozoic, Phanerozoic) and further subdivisions based on major extinction and evolutionary milestones.

Stromatolites

Layered sedimentary structures formed by prokaryotes binding thin films of sediment together, containing the earliest known cellular fossils dating back $3.5\text{ billion}$ years.

Acritarchs

Fossils of spinelike dinoflagellate-like protists dating to around $1.8\text{--}2.1\text{ billion}$ years ago, representing early single-celled eukaryotic organisms.

Horodyskia

A genus of fossilized red algae found in sedimentary rocks dating to $1.2\text{--}1.5\text{ billion}$ years old, representing the earliest definite multicelled eukaryotes.

Serial Endosymbiosis Theory

The theory that mitochondria and chloroplasts originated as free-living prokaryotes engulfed by ancestral eukaryotic host cells, evidenced by their circular DNA, prokaryotic ribosomes, and binary fission division.

Oxygen Revolution

A dramatic increase in atmospheric oxygen occurring $2.2\text{ billion}$ years ago after marine water became saturated with $O_2$ from photosynthetic cyanobacteria and single-celled eukaryotes.

Synapsids

A group of tetrapods originating $300\text{ million}$ years ago from which mammals evolved, exhibiting a progressive transition from an articular-quadrate jaw hinge to a dentary-squamosal jaw hinge.

Cambrian Explosion

A rapid radiation event $525\text{--}535\text{ million}$ years ago during which most major modern animal phyla, predators, and hard defensive armors/shells first appeared in the fossil record.

Permian Extinction

A mass extinction event $\text{252 million}$ years ago at the end of the Paleozoic Era caused by extreme volcanism during Pangaea formation, resulting in severe ocean anoxia.

Cretaceous Extinction

A mass extinction event $\text{65 million}$ years ago at the boundary of the Mesozoic and Cenozoic Eras triggered by an asteroid impact in the Gulf of Mexico, wiping out non-avian dinosaurs.

Pangaea

A supercontinent formed when Earth's landmasses merged together, occurring most recently $\text{251 million}$ years ago and driving massive environmental changes, extinctions, and allopatric speciation.

Adaptive Radiation

Periods of rapid evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill empty ecological niches left behind after extinction events.