History of Life on Earth and Systematics

Flashcard deck reviewing early Earth conditions, origin of life theories, evolution timeline, mass extinctions, systematics, taxonomic hierarchy, and phylogenetics from Chapters 25 and 26.

Reducing Atmosphere

An electron-adding atmosphere on early Earth that was thick with water vapor, nitrogen, carbon dioxide, methane, ammonia, and hydrogen.

Abiotic Synthesis Stages

The four sequential stages theorized for the origin of life: 1) synthesis of small organic molecules, 2) joining into macromolecules, 3) packaging into protocells, and 4) origin of self-replicating RNA.

Miller-Urey Experiment (1953)

A 1953 laboratory setup simulating early Earth conditions that produced amino acids and organic compounds from inorganic materials using electrical sparks.

Protocells

Droplets with membranes that maintained an internal chemistry different from their surroundings, representing Stage 3 in the origin of life.

RNA World Hypothesis

The hypothesis proposing that self-replicating RNA molecules acted as both genetic material and biological catalysts (ribozymes) before DNA-based systems evolved.

Stromatolites

Fossilized microbial mats built by cyanobacteria, representing the earliest direct fossil evidence of life from $3.5\,\text{billion years ago}$.

Oxygen Revolution

An event occurring $2.7\,\text{billion years ago}$ where cyanobacterial photosynthesis released $O_2$, causing the extinction of many obligate anaerobes and clearing the way for aerobic respiration.

Endosymbiosis

The process starting around $1.8\,\text{billion years ago}$ where a prokaryotic host cell engulfed an aerobic bacterium (becoming the mitochondrion) and a photosynthetic bacterium (becoming the chloroplast).

Cambrian Explosion

A sudden, immense diversification of animal phyla occurring in the fossil record approximately $535\,\text{million years ago}$.

Permian Extinction

A mass extinction event caused by extreme volcanism that wiped out $96\%$ of marine species.

Cretaceous Extinction

A mass extinction event caused by an asteroid impact that eliminated non-avian dinosaurs.

Adaptive Radiations

Periods of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles.

Continental Drift

The movement of Earth's tectonic plates that changes climates and separates landmasses, acting as a driver for allopatric speciation.

Phylogeny

The evolutionary history of a species or group of related species.

Systematics

A biological discipline focused on classifying organisms and determining their evolutionary relationships.

Taxonomy

The scientific discipline of naming and classifying organisms.

Binomial Nomenclature

The two-part scientific naming system devised by Carl Linnaeus, consisting of Genus + specific epithet.

Linnaean Classification System

A hierarchical framework for classifying organisms: $\text{Domain} \rightarrow \text{Kingdom} \rightarrow \text{Phylum} \rightarrow \text{Class} \rightarrow \text{Order} \rightarrow \text{Family} \rightarrow \text{Genus} \rightarrow \text{Species}$.

Homology

Similarity between structures in different species due to shared ancestry, such as whale flippers and human arms.

Analogy (Homoplasy)

Similarity between species due to convergent evolution rather than shared ancestry, such as bird wings and butterfly wings.

Monophyletic (Clade)

A phylogenetic group consisting of an ancestral species and all of its descendants.

Paraphyletic

A phylogenetic group consisting of an ancestral species and some, but not all, of its descendants.

Polyphyletic

A phylogenetic group consisting of distantly related species that does not include their most recent common ancestor.

Molecular Clock

A method used to estimate the absolute time of evolutionary change based on the observation that some regions of genomes appear to evolve at constant rates.