Stratigraphy and Geologic Time

Flashcards covering key concepts from the lecture on stratigraphy and geologic time.

What is the Principle of Superposition?

The Principle of Superposition states that in a sequence of sedimentary rocks, the oldest layers are at the bottom and the layers become progressively younger towards the top.

What cannot usually be radiometrically dated, and why?

Sedimentary rocks cannot usually be radiometrically dated because they are made of sediments that may have already undergone radioactive decay.

What period is known for the first multicellular organisms?

The Proterozoic Eon, specifically around 1.7 billion years ago.

What event marks the beginning of the Cambrian Period?

The Cambrian Explosion, a dramatic diversification of aquatic animal life.

Which eon is characterized by the dominance of dinosaurs?

The Mesozoic Era.

What are stromatolites?

Structures formed by cyanobacteria that trap particles of sediment, serving as records of early life.

What is radiometric dating?

Radiometric dating is a technique used to determine the absolute age of rocks by measuring the ratio of isotopes to decay products.

What significant event occurred at the end of the Permian Period?

The largest mass extinction in Earth's history.

During which geologic time frame did the first true mammals evolve?

During the Mesozoic Era.

What type of areas are characteristic for the Carboniferous Period?

Abundant swamps where amphibians thrived and coal was formed from rotting plants.

Name a significant characteristic of the Late Cretaceous Period.

It is often considered the apex of non-avian dinosaur diversity.

What evolutionary significance does the ichthyosaur have?

Ichthyosaurs were reptiles that adapted to an aquatic lifestyle, evolving features like paddle-like limbs and a streamlined body.

What major geological feature formed during the Permian Period?

The supercontinent Pangaea.

What did the Hadean Eon encompass?

The formation and early years of Earth, characterized by a tumultuous environment and the formation of the moon.

How do paleontologists estimate the age of fossils within sedimentary rocks?

By combining radiometric dating of surrounding igneous rocks with the Principle of Superposition.