Lecture 13 - History of Life, Paleontology, and Macroevolution

Comprehensive vocabulary flashcards covering the fossil record, geological dating methods, mass extinctions, early cellular origins, endosymbiosis, and the early evolutionary history of animals and chordates.

Paleontology

The scientific study of fossil organisms, including preserved mineralized skeletal parts (shells, teeth, bone), trace fossils, coprolites, and rare instances of soft tissues preserved in minerals or whole organisms trapped in amber.

Trace Fossils

Indirect paleontological evidence left by organisms rather than their preserved body parts, such as fossilized footprints, tracks, and burrows.

Coprolites

Fossilized animal feces and digestive remains that provide indirect evidence of prehistoric organism diets and behaviors.

Principle of Superposition

A foundational geological principle stating that in an undisturbed sequence of layered sedimentary rocks, each layer is older than the layer above it and younger than the layer below it.

Stratigraphy

The study of rock strata and layering used for relative dating, based on the record of Earth's history preserved within sedimentary rock layers.

Radiometric Dating

An absolute (chronometric) dating method that determines the age of sediments or fossils by measuring the known half-life of radioactive isotopes.

Uranium Series Dating ($\text{U-Series}$)

A radiometric dating method in which radioactive $^{238}\text{U}$ decays into stable lead ($\text{Pb}$) across a cascade of radioactive isotopes with distinct half-lives.

Argon-Argon ($^{40}\text{Ar}\text{-}^{39}\text{Ar}$) Dating

A radiometric dating technique frequently performed on volcanic rock that utilizes a decay system with a half-life of $1.25\text{ billion years}$.

Carbon-14 ($^{14}\text{C}$) Dating

A radiometric dating technique (radiocarbon dating) that measures the gradual loss of unstable radioactive $^{14}\text{C}$, which has a half-life of $5,730\text{ years}$.

Background Extinctions

The standard, continuous, and slow rate of extinction occurring under normal ecological conditions, accounting for approximately $96\%$ of all extinctions.

Mass Extinctions

Rapid, catastrophic events of global extent that wipe out a broad range of biological species across many lineages in a relatively short period of geologic time.

The "Big 5" Mass Extinctions

Five major mass extinction crises documented in the fossil record that severely impacted marine life and frequently marked the transitions between geological eras and periods.

Sixth Mass Extinction

The contemporary anthropogenic biodiversity crisis where the extinction rate is $100\text{ to }1000\times$ larger than the background rate, caused by habitat loss, hunting, and the introduction of non-native species.

Continental Drift

The large-scale movement of Earth's tectonic plates and landmasses over time (e.g., the supercontinent Pangaea $250\text{ million years ago}$), driving mountain building, species separation, and climate changes.

Domain Bacteria

A domain of unicellular prokaryotes present from Earth's earliest fossil records, characterized by cell walls containing peptidoglycan.

Domain Archaea

A domain of prokaryotic organisms distinct from bacteria, frequently thriving in extreme environments and sharing closer evolutionary relatedness to eukaryotes.

Domain Eukarya

The biological domain consisting of organisms whose cells possess a membrane-bound nucleus and specialized organelles, including protists, fungi, plants, and animals.

Photoautotrophs

Autotrophic organisms that synthesize organic molecules by capturing light energy via photosynthesis.

Chemoautotrophs

Autotrophic organisms that obtain metabolic energy by oxidizing simple inorganic compounds, such as ammonia ($\text{NH}_3$).

Heterotrophs

Organisms (such as animals) that cannot produce their own nutrients and must acquire energy by consuming pre-existing organic molecules, such as sugars.

Peptidoglycan

A structural polymer of sugars and amino acids that forms the cell wall surrounding the plasma membrane in most bacteria.

Stromatolites

Layered rock structures formed by colonies of photosynthetic cyanobacteria trapping sediments, representing Earth's oldest known fossils dating back $3.5\text{ billion years}$.

Banded Iron Formations

Layered sedimentary iron formations created around $2.5\text{ billion years ago}$ when biologically produced oxygen from photosynthetic cyanobacteria reacted with dissolved iron in the oceans, causing it to precipitate.

Endosymbiosis

The evolutionary process through which mitochondria and plastids (like chloroplasts) originated as small, free-living prokaryotes that were engulfed by ancestral host cells, retaining their own DNA and replicating similarly to bacteria.

Ediacaran Biota

An enigmatic assemblage of soft-bodied Precambrian organisms dating to around $600\text{ million years ago}$, representing the earliest known animal life prior to the evolution of vertebrates.

Hox Genes

A family of homeotic genes containing a conserved 180-nucleotide homeobox that code for anatomical positioning along the anterior-posterior body axis, representing one of the oldest animal synapomorphies.

Cambrian Explosion

A rapid macroevolutionary diversification occurring approximately $550\text{ million years ago}$ at the start of the Paleozoic Era, marked by the sudden appearance of most modern animal phyla and the first fossil chordates and vertebrates.

Burgess Shale

A renowned Cambrian fossil locality in Canada preserving soft-bodied organisms, complex skeletal armor, and the earliest evidence of predator-prey interactions.

Hallucigenia

An iconic spiny Burgess Shale fossil animal from the Cambrian period, displaying prominent dorsal spines and limbs that illustrate the emergence of defensive armor against predation.

Notochord

A flexible, longitudinal rod of support that runs along the dorsal side of the body, serving as a primary shared derived character (synapomorphy) of chordates.

Myotomes

Segmentally repeated blocks of skeletal muscle tissue arranged longitudinally in chordates that provide lateral locomotion.

Pikaia gracilens

A primitive Cambrian chordate fossil from the Burgess Shale ($530\text{ million years ago}$) that resembles modern lancelets and clearly displays a notochord and segmented myotomes.