Historical Geology 1404 Unit 1

What are: Eras (How were the boundaries between Eras picked?)

A Geologic time unit that consists of 2 or more periods. It is an Eon that is divided into smaller units. They are separated by catastrophic events.

Why has it been difficult to apply actual age-dates (numbers) to the Geologic Time Scale?

Because we did not have enough new raw data. Because the methodology (radio-mass spectrometer) had not been invented yet.

There are three types of unconformities based on:

They are based on the type and arrangement of rocks beneath the unconformity.

How are Formations named?

They are named by giving the formation a geographic name of a permanent feature near the location where the rocks are well exposed. If the formation consists of a single or dominant rock type theyn it is included in the name.

What are Biostratigraphic units?

They are stratigraphic units that contain fossil records.

What is a Series?

They are subdivisions of rock layers made based oth the age of the rock and corresponding to the dating sustem unit called Epoch

What are the general characteristics of Formations?

They consist of strata of specific origin type or characteristics mostly sedimentary. A formation could also be of metamorphic or igneous origin.

What is radioactive decay? What are the characteristics of radioactive decay?

When the nucleus of an atom becomes unstable and losses energy by emitting ionization radiation and changes to a different element. Constant for any particular radioactive isotope. Unaffected by any external conditions

What are the two types of varves?

Light layer which is sand/silt. Dark layer which is clay /organic matter

How far back in time can a year-by-year chronology be established using dendrochronology?

10,000 years

Know the names and correct order, from oldest to youngest, of the four Eons of the Geologic time Scale, and also the three Eras that comprise the Phanerozoic Eon.

4 Eons 3 Eras of the Phanerozoic Eon Phanerozoic Cenozoic Proterozoic Mesozoic Archean Paleozoic Hadean

What is Radiometric Age-dating? How is it done?

A method of dating materiel based on the decay of radioactive atoms. It is done with the mass spectrometer

What is a System?

A collection of elements or components that are organized for a common purpose.

What is a mass spectrometer, and when was it perfected?

A machine that separates isotopes, molecules and molecular fragments according to mass. 1950's

What is a Stratigraphic Section?

A sequence of layered rock in the order they were deposited.

What are: Eons

A time unit that consists of 20 or more Eras

What are: Epochs

A unit of geological time during which rock was deposited. It is a subdivision of a geologic period

What are varves?

An annual layer if sedimentary rock.

Name, define, and illustrate the three different types of unconformities. (Label the unconformity in each diagram): Nonconformity

An unconformity in which there are sedimentary rock layers (generally relatively flat-lying) above the unconformity, and crystalline rocks below the unconformity. (Crystalline rocks are intrusive igneous and metamorphic rocks.) Nonconformities are always erosional. A break of significant duration is inferred on the premise that igneous and metamorphic rocks are formed deep in the Earth's crust and exposed at the surface only after tremendous uplift and long, continuous erosion.

Name, define, and illustrate the three different types of unconformities. (Label the unconformity in each diagram): Disconformity

An unconformity in which there are sedimentary rock layers both above and below the unconformity, and the strata above are parallel to the strata below. (Generally, relatively flat-lying strata are seen to overlie relatively flat-lying strata.)

Name, define, and illustrate the three different types of unconformities. (Label the unconformity in each diagram): Angular Unconformity

An unconformity in which there are sedimentary rock layers both above and below the unconformity, but the strata above are not parallel to the strata below. (Generally, relatively flat-lying strata overlie tilted strata.) Angular unconformities are also always erosional and also imply a time break of significant duration. The underlying rock layers had to be tilted from their original horizontal position and beveled by erosion before the flat-lying strata above were deposited.

The Principle of Superposition

As layers accumulate through time, older layers are buried beneath younger layers. If geologists can determine which way was originally "up" in a stack of layers, they can put those strata in the correct historical order. (Rarely, after a sequence of layers has been deposited and compressed to form rock, it may be literally overturned by thrusting of the Earth's crust as continental plates collide. In these rare places the youngest rocks in a sequence are on the bottom, but such overturned sequences can be identified by the extensive faulting and breaking of rocks, and because the same original sequence of rocks is frequently present elsewhere in undisturbed order.)

Briefly describe four scientific methods, attempted in the late 1800s, to determine (incorrectly, as we now know) the actual age of the Earth. (What were the methods based on?)

Based on salinity of the oceans. Based on average rate of sediment deposition. Based on rates of evolution. Based on rate of heat loss from the Earth.

Why were accurate radiometric age-dates of minerals and rocks not possible until the 1950s?

Because the mass spectrometer was not perfected until then.

How can a geologist know the Period in which any particular sedimentary rocks were deposited?

By studying the fundamental principles in Geology and finding the relative age date

List the four assumptions used in Radiometric Age-dating:

Decay rate has been constant throughout geologic time (not really an assumption) 2. Measurements of amounts of parent isotope and daughter product are accurate 3. System was closed -- No parent or product was incorporated into or leaked out of the sample since the mineral or rock formed! 4. No daughter product was initially present when the mineral or rock formed (when the system became closed)

What is Actual Age-dating?

Determining the numerical age of rocks and geologic events for a particular area

What are facies changes? A facies change of sandstone to shale indicates:

Facies change describes the differing layers of geological strata. The sea level fell.

What did Hutton contribute to geology?

Father of modern geology. Hutton was the first to interpret rocks as products and records of the events in Earth's history, which lead to his principle that was later called Uniformitarianism. Credited with the discovery of "Deep Time. Stratigraphic Principles, Unconformities - a. Nonconformity b. Angular Unconformity c. Disconformity Principle of Unconformities Principle of Deformation Principle of Cross-cutting Relationships Principle of Inclusions

Which specific types of rocks can be radiometrically age-dated? Which generally can't?

Fossil bearing sedimentary rocks. Non classic rocks that do not contain isotopes

What did Kelvin contribute to geology?

He assumed that the earth has been loosing heat and that by measuring heat loss he could determine its age.

What did Cuvier contribute to geology?

He is the Father of Vertabrate Palentology. He discovered the Biological (Fossil) succession. Recognized many fossils were extinct organisms. Proposed that the history of the Earth was marked by repeated catastrophes. Each wiping out all life created new animals and plants.

What did Steno contribute to geology?

He suggested that all rock was originally formed as sediment was deposited from a fluid that covered the planet. As the rocks were forming, animal remains could be trapped and converted to fossils.His three principles; of superposition, of original horizontality, and of lateral continuity

With which method was Kelvin associated?

Heat Loss - he stated that the earth was cooling slowly

What did Smith contribute to geology?

His studies led to the recogition of the most important Stratagraphic Principle. Strata with the same Fossil assemblages are the same age using Guide Fossils

Define "Historical Geology"

Historical geology is a discipline that uses the principles and techniques of geology to reconstruct and understand the geological history of Earth.

Geology, as a science, really began with the studies and writings of ______________ .

Hutton

Who is credited with first recognizing the significance of unconformities?

Hutton

What are isotopes?

Isotopes are atoms with the same number of protons and electrons which give them the same atomic number and the same chemical reaction. They have different number of nuetrons giving them different atomic masses.

What are stratigraphic units?

It is a volume of rock based on identifiable origin and relative age range that is defined by the distinctive and dominate easily mapped features that characterize it

What is dendrochronology and what scientific uses does it have?

It is age dating method using tree rings. The tree ring represents a year in the life of a tree. The tree ring could be used because the light band is in the spring growing season and the dark band is winter. The width of the band can tell you if it was a good growing season or not.

What is 14Carbon Age-dating (Radiocarbon dating)? Why is it significant?

It is age dating that uses the 14Carbon from the atmosphere to age date. All plants and animals continually acquire C with this same ratio while alive, through photosynthesis and ingestion respectively.) After death of a plant or animal, no new 14C is assimilated, and the remaining 14C continues to slowly decay. 2. Age is determined by measuring how much 14 C is left, by comparing the carbon isotope ratio of a sample to the ratio for living organisms.

Define unconformity:

It is the contact between 2 rock units in which the upper unit is usually much younger than the lower one. Gap in the Geologic records: periods of time that are not represented by any rocks.

What is Catastrophism?

It is the theory that the Earth has been affected in the past by sudden short lived violent events possibly worldwide in scope- in contrast to uniformitarianism.

What is half-life? Why is half-life important?

It is the time it takes for half of the substance to undergo Radioactive Decay. It is important because radioactive elements decay at a constant rate and and estimate of the age of a rock or other materiel can be determined.

What materials can dated using 14C?

Most widely used method of age-dating ancient organic matter (wood, bone, teeth, shells).

What are: Periods (How were the names of Periods of the Geologic Time Scale derived?)

Periods are the basic unit of the geologic time scale. Geologic Time periods are named after the dominant rock types, geography mountain ranges and ancient tribes.

Igneous rocks from two different geologic settings have been used by scientists to estimate the actual age of boundaries on the Geologic Time Scale--what are they? (How have scientists been able to estimate the actual ages of the boundaries on the Geologic Time Scale?)

Precambrian/Cambrian Boundary

What is the role of fossils in recognizing and defining the subdivisions, and boundaries between subdivisions, of the Geologic Time Scale?

Provides geologists with a means for dating rocks fo a relative geologic time scale

What is Relative Age-Dating?

Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age, (i.e. estimated age).

What is Uniformitarianism?

States that present day processes have operated through out geological time.

Why is stratigraphy the key to understanding the history of the earth?

Stratigraphy is the science of rock strata, or layers. Layering occurs in sedimentary rocks as they accumulate through time, so rock layers hold the key to deciphering the succession of historical events in Earth's pas

What is the Geologic Time Scale?

Subdivides the geologic time into a hierarchy of increasingly shorter time intervals; each time subdivision has a specific name

What is a Formation?

The fundamental unit of lithostratigraphy geologic time markers based on the relative ages and the law of superposition. Usually sedimentary rock layers but could also be metamorphic rocks and volcanic flows. Igneous Intrusive rocks are generally not divided into formations.

What is Geologic Time?

The geological time scale (GTS) is a system of chronological measurement that relates stratigraphy to time, and is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships between events that have occurred throughout Earth's history.

What have we learned about Holocene climate from the glacial ice cores recently acquired by scientific drilling programs in Antarctica and Greenland?

The last 12,00 years have been stable by contrast to the last 800,000 years. Some climate changes during the glaciation have been very long, fairly rapid and wide spread. cooling happened in series of steps, warming some times in a single step.

Why does radiometric age-dating of minerals or rocks actually work?

The relative amounts of radioactive parent isotope and radiogenic daughter product in a mineral or rock is dependent only on the time that has elapsed since the atoms of the radioactive isotope were initially incorporated into the sample. In conventional radiometric age-dating, since the decay rate is known and constant, the age of a mineral or rock can be calculated from measurements of the relative amounts of radioactive parent isotope and radiogenic daughter product in the sample.

The Principle of Original Horizontality

When sediments are laid down on Earth's surface, they form horizontal or nearly horizontal layers. This means that non-horizontal rock layers were tilted or folded after they were originally deposited.

What are Guide fossils? What are Guide fossils used for?

a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found. They can be used to date the rock layer in which it is found

List the four chief methods (isotope pairs) used in Radiometric Age-dating of rocks & minerals:

a. 238U -- 206Pb b. 235U -- 207Pb c. 40K -- 40Ar d. 87Rb -- 87Sr

What did Werner contribute to geology?(What is Neptunism?) (What is Vulcanism?)

founding of geology as a science the erroneous theory that rocks such as granite were formed by crystallization from the waters of a primeval ocean. is the geologic theory that the rocks forming the Earth were formed in fire by volcanic activity, with a continuing gradual process of weathering and erosion wearing away rocks, which were then deposited on the sea bed, re-formed into layers of sedimentary rock by heat and pressure, and raised again. It proposed that basalt was solidified molten magma

What is stratigraphy? What are the Stratigraphic principles primarily used for?

is a branch of geology which studies rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. It is primarily used in the study of sedimentary and layered volcanic rocks.

What is "Deep Time?"

the multimillion year time frame within which scientists believe the earth has existed, and which is supported by the observation of natural, mostly geological, phenomena.

Principle of cross cutting relationships

when one geological feature cuts through another, the former is the younger and the latter is the older of the two features.

Principle of Fossil (Biologic) Succession

which states that fossils occur in a consistent vertical order in sedimentary rocks all over the world.