Essentials of Geology 3rd Edition Chapter 10 Study Cards - Deep Time
Principle of Uniformitarianism:
Simply states that physical processes we observe today also operated in the past at roughly the same rates and were responsible for the frmation of the geologic features we see in outcrops. Means the present is key to the past. This meant that the Earth was much older than human history; geologic processes work very slowly.
Relative Age vs. Numerical Age
Relative Age: Age of a feature with respect to another.
Numeric Age: The age of a feature in given years.
Found ways of defining relative age long before they did for numerical age.
Principles leading to relative-age determination.
U, H, S, C, C-C R, BC, INC
Uniformitarianism, Original Horizontality, Superposition, Original Continuity, Cross-Cutting Relations, Baked Contacts, Inclusions.
Principle of Uniformitarianism:
Principle of Uniformitarianism:
Physical processes we observe operating today also operated in the past at roughly comparable rates.
Principle of Original Horizontality:
Original Horizontality: Sediments on Earth settle out of a fluid in a gravitational field. Typically the surface on which sediments accumulate (such as a floodplain or a bed of lake or sea) are fairly horizontal. When we see folds and tilted beds, we are seeing the onsequences of deformation that postdates deposition.
Principle of Superposition
Principle of Superposition: In a sequence of sedimentary rock layers, each layer must be younger than the one below, for a layer of sediment cannot accumulate unless there is already a substrate on which it can collect. Thus, the layer at the bottom of a sequence is the oldest, and the layer at the top is youngest.
Principle of original continuity:
Principle of Original Continuity: Sediments generally acumulate in continuous sheets. If today you can find a sedimentary layer cut by a canyon, then you can assume that the once spanned the canyon but was later eroded by the river that formed the canyon.
Principle of Cross-Cutting Relations:
Principle of Cross-Cutting Relations: If one geologic feature cuts across another, the feature that has been cut is older. For example, if an igneous dike cuts across a sequence of sedimentary beds, the beds must be older than the dike. If a fault cuts across and displaces layers of sedimentary rocks, then the fault must be younger than the layers.
Principle of Baked Contacts:
Principle of Baked Contacts: An igneous intrusion "bakes" (metamorphoses) surrounding rocks. The rock that has been baked must be older than the intrusion.
Principle of Inclusions:
Principle of Inclusions: If a layer of sediment deposited on an igneous layer includes pebbles of igneous rock, then the sedimentary layer must be younger.
If an intrusion contains fragments of antoher rock, the fragments must be older than the intrusion.
The fragments (xenoliths) in an igneous body and the pebbles in the sedimentary layer are inclusions or pieces of one material incorporated in another. The rock containing the inclusion must be younger than the inclusion.
Geological history is developed of the region when the relative ages of the events that took place there are defined.
Fossil Succession/Principle of Fossil Succession:
A particular assemblage of fossil species can be found only in a limited interval of strata, not above or below this interval. Thus, once a fossil species disappears at a horizon in a sequence of strata, it never reappears higher in the sequence. In other words, extinction is forever. This is the principle of fossil succession.
PRINCIPLE OF FOSSIL SUCCESSION
Unconformity is a surface representing a period of nondeposition and possibly erosion. Sequence of rocks in a bed. Verticle layers.
Rocks below an angular uncomformity were tilted or folded BEFORE the unconformity developed. Thus, an angular unconfirmity cuts across the underlying layers, the layers below have a different orientation from the layers aboe. Angular unconformities form where rocks were tilted by either folding or faulting, before being exposed at the Earth's surface.
Nonconformity is a type of unconformity at which sedimentary rocks overlay intrusive igneous rocks and/or metamorphic rocks.
Disconformity is when a sequene of sedimentary beds has been deposited beneath a shallow sea. The sea level drops, exposing the recently deposited beds for some time. During this time, no new sediment accumulates, and some of the pre-existing sediment gets eroded away. Later, sea level rises and a new sequence of sediment accumulates over the old. The boundaries between the two sequences is the disconformity. Even though the beds above and below are parallel, the contact between them represents an interruption in deposition.
Because of unconformities, the record preserved in the rock layers is incomplete.
Stratigraphic Columns Stratigraphic Formations
Stratigraphic Formations (Formations) are a sequence of beds of a specific rock type or group of rock types that can be traced over a fairly broad region. The boundary surface between two formations is a type of geologic contact.
Geologists name a formation after a locality where it was first identified. If the formation consists of only one rock type, the rock type may be incorporated into the name. But if the formation contains more than one rock type, the word formation is used in the name (Toroweap Formation). Several adjacent formations in a succession may be lumped togethr as a stratigraphic group.
Defining the age relationship between the strata at one locality and the strata at another.
Lithologic correlation: Correlate formations between nearby regions based on similarities in rock types. Before deformation and/or erosion, the layers that correlate may be continuous.
This is when rock units are being correlated over broad areas - fossils are relied upon to define the relative ages of sedimentary units. If fossils of the same age appear in two separate locations, the strata at the two locations correlate.
Portrayal of distributions of formations. For identification of geological structures.
By correlating rocks from locality to locality in millions of places around the world, geologists have pieced together a composite stratigraphic column, called the geologic column that represents the entire of Earth history. It is divided into segments which represent a specific interval of time.
ANTICLINE & SINCLINE
GEOLOGICAL TIME SCALE
Hadean, Archean, Proterozoic, Panerozoic Eons.
(These constitute the Precambrian)
zoic means life
The earliest life was
Bacteria and archea which appeared during the Archaen Eon.
In the Phanerozoic Eon, organisms with ? became widespread
hard shells and later skeletons
In Precambrian time only ? existed
small organisms with no shells
Phanerozoic Eon is subdivided into eras.
From oldest to youngest: Paleozoic (ancient life); Mesozoic (middle life); and Cenozoic (recent life) Eras.
Each era is divided into periods and each period is divided into epochs.
These names refer either to localities where a fairly complete stratigraphic column representing the time interval was first identified or to a characteristic of the time.
Appearance of invertebrates with shells defines the Precambrian-Cambrian boundary. At this time, there was a sudden diversification in life, with many new genera appearing over a relatively short interval - the CAMBRIAN EXPLOSION.
First vertebrates, fish, appeared during this period:
Land plants spread over the continents in this period:
Amphibians appeared during this period:
Reptiles evolved during this period;
Dinosaurs did not walk the land until this:
Triassic and stayed until end of cretaceous period
The age of mammals is the:
Cenozoic Age - The Age of Mammals
Birds first appeared during Mesozoic (beginning of cretaceous period), but underwent great diversification in Cenzoic era.
A species that existed for a short time, but over a wide area.
How do we determine NUMERICAL AGE:
Things changed with the discovery of radioactivity. Radioactive elements decay at a constant rate that can be measured in labs and specified in years. Was once called radiometric dating, but has been changed to ISOTOPIC DATING.
All atoms of given element have same number of protons in their nucleus. This is the atomic number. However, not all atoms have the same number of neutrons in their nucleus. Therefore, not all atoms of a given element have the same atomic weight. This is roughly the number of protons plus neutrons. Different versions of the element are called ISOTOPES. Isotopes have same atomic number but different atomic weight. Some isotopes of an element are stable, meaning that they essentially last forever. Radioactive isotopes are unstable: after a given time they undergo a change called RADIOACTIVE DECAY. Radioactive Decay converts them into a different element.
Radioactive Decay converts elements into a different element. It can take place by a variety of reactions that change the atomic number of the nucleus and thus form a different element. In these reactions, the isotope that undergoes decay is the PARENT ISOTOPE. The decay product is called the DAUGHTER ISOTOPE. It is what the element decays into.
Isotope that undergoes decay. Daughter isotope is left.