Historical Geology Test

What is relative dating?

a method used in geology to determine the sequence of rock layers based on their position in relation to one another (WITHOUT SPECIFIC AGES)

What are Steno’s 4 laws of stratigraphy?

Principle of Horizontality, Law of Superposition, Cross-Cutting Relationships, and Correlation

Principle of Horizontality

says that sediment is put down in flat horizontal layers. If something causes them to be flat, it had to have happened after they were formed.

Law of Superposition

in an undisturbed sequence of sedimentary rocks, the oldest will be on the bottom and the youngest will be on the top; youngest rock layers are laid on top because they are laid down last

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 erosions (removes layers of rocks)

Absolute Dating

a type of dating that can give a reliable age on something; more accurate - Looking at chemical components to determine how old a rock or fossil actually is.

Isotope

form of an element that has a different of neutrons, have excess energy in their nucleus and are unstable, unstable nuclei break apart or decay, process of decay is called radioactivity.

Radiometric Dating

unstable atoms break down into stable atoms; this time it takes is measurable. Main type of absolute dating, calculates age based on the amount of radioactive isotopes. Highly accurate

Half-Life

TIME it takes for half of the unstable parent atom to decay into a stable daughter atom

Carbon-14

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

Uranium-238

used to date rocks and goes back to 4.5 billion years

Radioactive and stable molecules in a substance can be measured to determine

age

The older something is the ______ radioactive isotopes and ____ stable molecules

fewer; more

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 or 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 and can capture organisms and preserve them; Ice and tar can also preserve

Trace Fossils

indirect evidence of ancient life. Can include footprints, burrows, caprolites, and even 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 thin film of carbon; mostly plants but sometimes animals

Impression Fossils

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

Index Fossils

the best type of fossil for correlation, 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, also preserves well because of fast burial

Natural selection

organisms that had traits that helped them survive and reproduce passed on their genes

When sedimentary rocks form under certain conditions this can tell us about the what?

climate

Virginia fossils are found where?

Mostly in the Coastal Plain, Valley & Ridge, and Appalachian Plateau

Most Virginia fossils are

marine organisms

Geological Time Scale

based on the appearance/disappearance of organisms and relating stratigraphy through time

Precambrian Era Year

4.5 billion years ago - 570 million years ago, lasted 4 billion years and longest division of geologic time (88% of Earth’s history)

Precambrian Era Rocks and Fossils

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

Precambrian Era Atmosphere

No OXYGEN in the beginning, all life was anaerobic (did not need oxygen to survive) oxygen developed 600 million years ago at the end of the Precambrian, formed as a by-product of photosynthesis from cyanobacteria

Paleozoic Era Year

540-248 million years ago, second largest period of time in Earth’s history. Divided into periods: Cambrian, Ordovician, Silurian & Late: Devonian, Mississippian, Pennsylvania, Permian

Paleozoic Era Landmasses

Early: two large landmasses; Laurasia: North America, Europe, Siberia. Gondwana: South America, Africa, China, India, Australia, Antarctica

Late: Laurasia and Gondwana collide and form one single supercontinent: Pangaea (also formed the Appalachian Mountains)

Paleozoic Era Life

Early: Cambrian Explosion: life diversified in the Cambrian, large number of fossils (Ex: Trilobites, brachiopods, mollusks (clams, oysters))

Late: Evolution takes off and all ancestors of modern organisms formed

Paleozoic Era Atmosphere

Oxygen and Nitrogen

Permian Extinction

Mass extinction of 95% off all marine life, possibly caused by volcanic eruptions which led to major climate change

Mesozoic Era Year

248-65 million years ago

Mesozoic Era is also called

Age of Reptiles, or Age of Dinosaurs

Periods: Triassic, Jurassic, Cretaceous

Mesozoic Era Landmasses

in early Mesozoic, Pangaea breaks apart and forms continents that we know today. By the end of the Mesozoic, most continents are placed near where we see them today

Mesozoic Era Life

Survivors of extinction: reptiles, seed-bearing plants, insects, some fish and amphibians. Evolution of flowering plants and birds

Cretaceous Mass Extinction

Asteroid Impact: and asteroid around 300 miles in diameter impacted Earth

Climate Change: massive cooling period around 65 mya

Sea level change: sea levels dropped around 65 mya which could have affected climates

Cenozoic Era Year

65 million years ago - present

Cenozoic Era is also called

Age of Mammals

Periods: Tertiary and Quaternary

Cenozoic Era Landmasses

all continents are in their current position, 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

C14 dating

a method used to determine the age of organic materials, specifically those that were once living

(Free response) How are Petrified fossils formed?

organic material gets replaced with minerals

(Free response) How are Index fossils formed?

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