Historical Geology Test Study Guide 21-22

These flashcards cover key concepts from the Historical Geology study guide, including relative and absolute dating, fossil types, significant geological eras, and major extinction events.

What is Relative Dating

Rock layers are placed in their proper sequence or order chronologically (without specific ages)

What are Steno’s 4 laws of Stratigraphy

Principle of Horizontality

Law of Superposition

Cross-Cutting Relationships

Correlation

Principle of Horizontality

Sedimentary rock layers are deposited in horizontal or nearly horizontal layers and if they’re not horizontal then something happened after they formed

Law of Superposition

In any undisturbed sequence of sedimentary rocks, the oldest layers are at the bottom and the younger layers are at the top

Cross-Cutting Relationships

faults, folds, inclusions, and igneous intrusions are younger than the rocks they cut through

Correlation

Compares rocks in different locations for similarities in formation, time, and fossils

Unconformity

Gaps in the rock record or missing time caused by weathering and erosion (removes layers of rock)

Absolute Dating

A type of dating that can give us a reliable age on something more accurate-looking at the chemical components how old a rock or fossil actually is

Chemically Basics

An isotope is a form of an element that has a different amount of neutrons

Isotopes have excess energy in their nucleus and are unstable

These unstable nuclei spontaneously break apart or decay

This process of decay is called radioactivity

Radiometric Dating

Unstable atoms break down (decay) into stable atoms; this time it takes is measurable

Main type of absolute dating. Calculates age based on the amount of radioactive isotopes

When unstable atoms like Carbon-14 lose electrons and becomes stable; highly accurate

Half-Life

Time it takes for half of the unstable parent atoms to decay into a stable daughter atoms

Scientists can measure how much radioactive and stable molecules are in a substance to determine its age

The older something is the fewer radioactive isotopes and more stable molecules

Carbon-14

is used to date things once alive (can go back no more than 50,000 years) Ex. teeth, bones, shells

Uranium-238

is used to date rocks and goes back 4.5 billion years

What is a Fossil

Preserved remains or traces of an organism

Petrified Fossils

Organic material gets replaced with minerals; A dinosaur bone feels more like rock than bone; Wood can also be petrified

Molds and Casts

Molds are created when a shell organic structure is buried and then dissolves; If the mold is then filled in with minerals it is called a cast

Unaltered Remains

Some fossils are preserved with little actual change; Amber is hardened tree sap can capture organisms and preserve them; Ice and tar can also preserve

Trace Fossils

Indirect evidence of ancient life. Can include footprints, burrows, caprolites (fossilized crap or stomach content) and gastroliths (stomach stones); Gives clues on how they lived, where, what they ate, or how they cared for young

Compressional Fossils

2D organic remains that happen pressure squeezes out the liquid and gases of an organism leaving behind a thing film of carbon; Mostly plants but sometimes animals

Impression Fossils

2D fossils that do not contain organic matter and commonly show internal structures

Correlation

Fossils enable scientists to correlate rock layers, infer past environments and provide evidence of evolution

Fossils tend to be found in the same general order at different locations

This allows geologists to correlate rock layers based on fossils

Index Fossils

The best type of fossil for correlation is the index fossil

Index fossils are from organisms that only lived a short time but in a really widespread area

Volcanic Ash

Volcanic Ash can act like an index fossils because it can be seen in a widespread area, but an eruption is usually a short lived event

Can be used to in relative dating

It can also preserved well because of the fast burial of organisms

Changes

Fossils show us that life has changed over time or evolved

Organisms that had traits that helped them survive and reproduce passed on their genes called natural selection

Climate

Sedimentary rocks form under certain conditions and these conditions can tell us about the climate

Limestone forms in warm, shallow, and tropical seas like Bahamas today

There’s limestone in Roanoke and corals have been found in West Virginia

Virginia Fossils

Virginia fossils are found mostly in the Coastal Plain, Valley and Ridge, and Appalachian Plateau provinces

Most of Virginias fossils are of marine organisms

This indicates that large areas of the state have been periodically covered by seawater

Geologic Time Scale

Based on the appearance/disappearance or organism and relating stratigraphy though time

Evolution

change in a species over time

Species

any group that can reproduce and produce fertile offspring

Surviving offspring have beneficial genetics that allow them to adapt to changing environments

Precambrian Era

4.5 billion years ago - 570 million years ago

Lasted 4 billion years and is the longest division of geologic time (88% of Earth’s history)

Rocks and Fossils

Rock record is incomplete because many layers have been removed from weathering and erosion or changed/deformed due to plate tectonics

There are very few fossils during this era because the first life was primitive without hard parts to fossilize

Atmosphere

There was no oxygen in the beginning

All life was anaerobic; they didn’t need oxygen to survive

Oxygen developed around 600 million years ago at the end of the Precambrian

It is formed as a by-product of photosynthesis from cyanobacteria

Paleozoic Era

540-248 million years ago

Second longest period of time in Earth’s history

Divided into periods: Early Cambrian, Ordovician, Silurian and Late: Devonian, Mississippian, Pennsylvania, Permian

Landmasses

EARLY: There were two landmasses in the early Paleozoic

Laurasia: North America, Northern Europe, Siberia

Gondwana: South America, Africa, China, India, Australia, Antarctica

LATE: Laurasia and Gondwana collide and form one single supercontinent: Pangaea

This collision formed the Appalachian Mountains

Life

EARLY: Cambrian Explosion: Life diversified in the Cambrian and there were a large number of fossils during this time (Ex. Trilobites, brachiopods, mollusks which are clams and oysters)

LATE: Evolution really takes off and all ancestors of modern organism formed

Atmosphere

Oxygen is now in the atmosphere (similar make-up as current day) from cyanobacteria

2 most elements: Nitrogen and Oxygen

Permian

Mass extinction of 95% off all marine life

Probably caused by volcanic eruptions which brought about major climate change

Mesozoic Era

248 - 65 million years ago

Called the Age of the Reptiles or the Age of Dinosaurs

Periods: Triassic, Jurassic, Cretaceous

Landmasses

In early Mesozoic, Pangea breaks apart and forms the continents that we know today

By the end of the Mesozoic, most continents are placed near where we see them today

Life

Survivors of extinction: reptiles, seed-bearing plants, insects, some fish, some amphibians

Age of Reptiles because reptiles the continent land animals (dinosaurs)

Evolution of flowering plants and birds

Asteroid Impact

An asteroid around 300 miles in diameter impacted Earth

Climate Change

There was a major cooling period around 65 mya (possible dust in the atmosphere from the impact could have decreased the amount of heat from the Sun the Earth received)

Sea level change

Sea levels dropped around 65 mya which could have affected the climates

Cenozoic Era

65 million years ago-present

Periods: Tertiary, Quaternary

Cenozoic Era (landmasses)

All continents are in their current positions

Major volcanism and mountain building occurs (Himalayas and Alps)

Cenozoic Era (Life)

Many angiosperms (flowering plants) and few gymnosperms (cone bearing plants)

Evolution of modern plants and animals

Human Evolution

What is C

Igneous Intrusion

What are the events in order

C

B

H

D

F

I

G

A

E