Paleontology and Geochronology Flashcards

Which radiometric dating method is most appropriate for dating volcanic rocks that are 1–10 million years old?

Answer: Potassium-Argon (K-Ar)

Potassium-Argon dating (half-life of ⁴⁰K = 1.25 Ga) is well-suited for volcanic rocks in the 1–10 Ma range because argon gas is completely lost when lavas erupt, resetting the clock.

Graptolites are most useful as index fossils for which geologic periods?

Answer: Ordovician and Silurian

Graptolites (colonial hemichordates) were abundant planktonic organisms from the Cambrian through Carboniferous, but are most widely used as zone fossils for Ordovician and Silurian correlations.

The principle of faunal succession states that:

Answer: Fossil assemblages succeed one another vertically in a definite and determinable order

William Smith's principle of faunal succession establishes that different strata contain different characteristic fossil assemblages, and these assemblages appear in a consistent vertical sequence that can be recognized worldwide.

A disconformity is a type of unconformity characterized by:

Answer: Missing strata between parallel beds with no angular discordance

A disconformity occurs where parallel sedimentary layers are separated by a surface of erosion or non-deposition, representing a time gap without angular discordance between the units.

The Mesozoic Era is commonly referred to as the 'Age of' which organisms?

Answer: Reptiles (including dinosaurs)

The Mesozoic Era is called the 'Age of Reptiles' because dinosaurs, marine reptiles (plesiosaurs, mosasaurs), pterosaurs, and other reptilian groups dominated terrestrial and marine ecosystems.

The Uranium-Lead (U-Pb) isotope system using zircon crystals is preferred for dating the oldest Earth rocks because:

Answer: Zircon incorporates uranium but rejects lead at crystallization, providing a reliable clock

Zircon incorporates uranium into its crystal lattice while excluding lead at formation, so any lead present represents radiogenic decay product, giving a reliable age; its chemical durability also survives metamorphism and erosion.

Coccoliths are the calcite plates produced by which type of marine microorganism?

Answer: Coccolithophores (calcareous algae)

Coccoliths are microscopic calcium carbonate (calcite) plates secreted by coccolithophores, single-celled phytoplankton that are major contributors to deep-sea ooze and chalk deposits since the Triassic.