Units 28-29 Flashcards
What is deep time?
Time that stretches back a LOOOONNNG time ago. billions of years
Uniformatarianism
The idea that the laws of nature do not change with time.
aka. Time symmetry
Occam’s razor
If two or more explanations exist for the same physical phenomenon, we choose the simplest that satisfies all the observations.
Relative time
The determination of the sequence in which events occurred, relative to each other.
Think “timeline” game
Absolute time
A numeric or quantitative measure of time
What is another name for absolute time?
Numeric or quantitative time
What are the 5 principles of relative dating that we will talk about in class?
- Original horizontality
- Superposition
- Inclusions
- Cross-cutting relationships
- Faunal succession
Original horizontality
Sedimentary rocks are deposited in horizontal layers. They are FORMED horizontally
So we can analyze ancient sediment to determine age
Principle of superposition
In a stack of sedimentary layers (split by different composition), the oldest layer will be on the bottom and the youngest on the top
Principle of inclusions
Inclusions within the rock.
Solid materials (like pebbles) enclosed within another solid are OLDER than the rock that encloses them.
Inclusions
Rock, fragment of rock, or fossil enclosed within another rock.
Ammonites
The name given to the fossil shell remains of animals that lived in the oceans millions of years ago, but are now extinct.
Squidlike (nautilus stuff)
Fault
A break in earth’s lithosphere where rocks on one side of the break have slipped past the rocks on the other side.
True or False: Faults are CREATED by earthquakes.
True
Principle of cross-cutting relationships
Rocks are OLDER THAN the features (like faults) or rocks that cross-cut them.
Trilobites
A common animal that lived in earth’s oceans during the paleozoic era. Horseshoe crab, pillbug features
Principle of faunal succession
Within stacks of sedimentary rocks, there is a pattern of change in the types of fossils the layers contain.
The fossils can therefore help us determine the relative age of different layers.
True or False: Rock layers often have distinct groups of fossils.
True
Unconformity
A break or gap in the geologic record
What kinds of unconformities are found in our geologic history?
Sedimentation stopped in some areas, sedimentary layers formed many feet below the surface of the ocean and were then lifted high above sea level to be eroded away, natural events destroyed layers, etc.
Parent and daughter isotopes
The result of radioactive decay, in which one element decays to form another element.
The starting element = parent
New element formed from decay process = daughter
Why do geologists use two or more isotopic systems to date rocks?
For greater accuracy, to verify results
Where does carbon-14 come from?
Once living organisms
True or False: the different minerals within the same rock can be formed at different times
True
Events
A happening that occurs at a particular point in space at a definite time.
Fission-track dating
A type of radioactive decay clock that uses the trails or tracks created by uranium fission decay to determine the age of geologic events.
Period
A subdivision of geologic time. Smaller than an era, but still several tens of millions of years long.
True or False: The ages obtained by these methods represent the ages of the elements that make up the rocks or minerals
FALSE
Geologic column
A chart that shows the subdivisions of geologic time
Era
The largest subdivision of geologic time
How many eras are there?
4
What are the four eras?
- Cenozoic
- Mesozoic
- Paleozoic
- Precambrian
What does cenozoic mean?
Recent life
What does mesozoic mean?
middle life
What does paleozoic mean?
ancient life
What was the era of dinosaurs?
Mesozoic
What is magma?
Molten rock, under the crust
Igneous
the type of rocks produced when melted material solidifies
Sedimentary
The type of rocks created from sediments weathered from other pre-existing rocks.
Metamorphic
The type of rocks produced when pre-existing rocks are altered without melting by pressure and heat.
Protolith
A pre-existing rock from which other rocks are formed
What does protolith mean?
Precursor rock
Rock cycle
the transformation of igneous, sedimentary, and metamorphic rocks from one type to another.
True or False: All three types of rocks can transform into the other two rock types OR into another version of itself.
True
Minerals
the basic building blocks of rocks - elements joined together naturally
True or False: All materials in a rock are classified as minerals
False
Characteristics of a mineral:
- naturally occurring
- inorganic solid
- has a fixed or narrowly limited chemical composition
- has a definite internal crystal structure
- exists within a defined range of pressure, temperature, and moisture
- Has a unique set of physical properties
True or False: Ice is a mineral
True
True or False: glacial ice can be considered a rock
True
What is the most abundant mineral group in the Earth’s crust?
Silicates
True or False: The mantle does not melt at one temperature and pressure, it melts over a RANGE of temperature and pressure combinations.
True
Why does the mantle melt at a range of different temperatures and pressures?
Because it’s made up of many different materials, each of which has a different melting temperature
True or False: In addition to the decompression, a solid rock can melt into magma if the chemistry of the rocks change.
True
How do you change a rock’s chemistry?
Add water
How is water added to the mantle?
Oceanic crust descending down into the mantle, bringing minerals that have water in their crystal lattices. When the minerals heat up, they break down and release the water.
Plutonic
Pertaining to igneous rocks formed beneath Earth’s surface
Volcanic
Pertaining to igneous rocks formed ON earth’s surface
Physical weathering
Breaking down rocks through physical processes like freezing and thawing.
Talus
A sloping mass of rocky fragments at the base of a cliff. Cone shaped
How is physical weathering usually accomplished?
Through water and ice, freezing and expanding.
But also wind, falling rocks, roots of trees and shrubs, etc.
Chemical weathering
Breaking down rocks through chemical processes like acidic reactions.
Metastable
A mineral that is unstable when subject to temperatures and pressures different from those of its formation but not liable to spontaneously change.
Dissolution
To break apart or dissolve in solution.
True or False: Water in soils or shallow rocks is often acidic because of water’s reaction with carbon dioxide.
True
Fun fact: CO2 is often 25 or more times higher in soils than in the air we breathe
woah
Clasts
A grain of rock material weathered from a pre-existing rock
Strata
A layer of material, often one of several layered upon one another.
True or False: All clastic rocks require cement
True
True or False: Clastic sedimentary rocks are classified according to the size of their grains.
True
What size clasts are needed for a rock to be “conglomerate”?
> 2 mm in diameter
What size clasts are needed for a rock to be “sandstone”?
<2 but > 1/16 mm
What are the smallest types of clastic sedimentary rocks?
Shale
True or False: Virtually all fossil fuels are formed in and extracted from igneous rocks
FALSE
What type rocks do we find fossils in?
Sedimentary
Foliation
The structural or chemical arrangement into layers of materials in a rock.
Like physically visible I think
Do metamorphic rocks transform in a solid or liquid state?
Solid
Where do metamorphic rocks come from in the crust?
Deep, where temps and pressure are highest.
How do deeply buried metamorphic rocks get to the surface of earth?
Tectonic movements
True or False: Examining the layers of foliation in metamorphic rocks can provide us with information about past tectonic events
True
True or False: The rock cycle is responsible for the soil that provides roots for ALL LIFE
True
Why are volcanoes formed at subduction points?
Because when the oceanic plate goes underneath another one, it creates pressure. Pressure supplies energy (electrical that leads to chemical reactions). Enough pressure leads to the water molecules being torn apart and interacting with other minerals in the area. This lowers the melting temperature. When temp is lowered, the rock melts and comes bubbling up to form volcanoes (like that video of Tonga volcano).
What do all rocks within the type of rock (igneous, sedimentary, metamorphic) have in common?
Minerals
Precipitate
A solid formed inside a liquid by a chemical reaction.
Hydrothermal circulation
Movement or circulation of hot water.
Hydrolysis
A type of chemical weathering in which water interacts with the minerals in the rock to form new minerals and leave ions in the water. Silicate-rich rocks and carbonate-rich rocks often experience this type of chemical weathering.
Oxidation
A type of chemical weathering in which water interacts with the minerals in the rock to form new minerals and leave ions in the water. Metal-rich rocks often experience this type of chemical weathering.
True or False: Many rocks don’t form on the surface of the earth. They’re formed within the crust or mantle and then pushed up to the surface to be eroded.
True
Why do igneous rocks have large mineral deposits?
Because they form underground so the cooling time is longer.
True or False: Igneous rocks can form above ground
True
What happens to igneous rocks that cool above ground?
They cool and solidify very quickly, so there’s no time for large minerals to form and they’re often microscopic. Sometimes, like in the case of obsidian, there are no minerals at all.
What is responsible for making most limestone?
Organisms making CaCO3
Why does foliation occur?
Pressure is typically being applied in one direction, not uniformly in all directions (cuz gravity always pulls down)
True or False: All metamorphic rocks are foliated
False
True or False: Foliation always manifests PERPENDICULAR to the force.
True
