1st exam Flashcards
How is Historical Geology studied?
With the Scientific Method!
The scientific method is used to…
- Propose
- Test
- Provide evidence FOR or AGAINST a given HYPOTHESIS.
What is the Scientific Method?
an educated, untested explanation
What are the steps for the scientific method?
- make observations or identify problems
- make hypotheses to explain observations
- gather evidence to test hypotheses
- reject hypotheses (ideally all but one)
Remaining hypothesis is the most probable!
What are plate tectonics?
Thin plates that cover Earth’s surface
What marks the positions of plate boundaries?
Earthquakes!
How fast do plates move (relative to each other)?
a few cm/yr (average)
-> about as fast as nails grow
What are plates composed of?
AKA: Lithosphere, are composed of crust + upper mantle.
What are the two kinds of lithosphere (plates)?
- Oceanic
- Continental
Plate motion caused by CONVENTION in the mantle is:
density-driven cyclical motion of materials, caused by heat. Ex: When you boil water!
Plates are separated by Plate Boundaries, what are the 3 major types?
-Divergent (heading away : )
-Convergent (coming together: –>
<– )
There are two kinds of Divergent plate boundaries… what are they?
- mid ocean ridge
- continental rift
There are three kinds of Convergent plate boundaries… what are they?
- Oceanic-oceanic
- Oceanic-continental
- Continental-continenal
What is subduction?
when one plate dives under another (less dense goes over, more dense goes under)
Where does a volcanic island arc form?
forms on overriding plate
What is a trench?
A deep V-shaped intersection of 2 plates
Where does a back-arc basin form?
Forms behind islandic arc
Oceanic-oceanic plate boundaries (convergent) feautures……?
- Subduction
- Volcanic islandic arc
- Trench
- Black-arc basin
What do Oceanic-Continental convergent Plate Boundaries feature?
-Subduction
=>volcanoes
-Crumpled continent
=>tall mountains
-Trench
-This is how ocean basins get smaller or close!
-Also affected by accretion.What is accretion?
-Scraped &/or collided materials piled up on continents edge. (One way that continents get bigger!)
What do Continental-Continental convergent P.B’s feature?
-NO subduction,
=> HUGE interior mountain range
-Modern ex. Himalayas
-Few volcanoes
-This is another way that continents get bigger, and ocean basins close!What type of plate boundaries has plates that slide past each other?
Transform
What do transform plate boundaries feature?
-offset rivers, roads, etc
-no net gain/loss of crust
-no mountains
-no volcanoes
(modern ex. San Andreas Fault)
Which plate boundary connects _____ and convergent P.B’s?
Tranform! (connects divergent and convergent p.b’s!)
Who was Alfred Wegener?
A German meterologist (1912) who proposed the existence of a “supercontinent” (Pangaea) and continental drift!
(basically the man given credit for the discovery of Plate Tectonics)
What was Wegener’s evidence?
- Coastlines match
- Glaciation patterns
- Distribution of ancient equatorial climate belts
- fossil distribution
- matching rocks, oceans apart.
What is paleomagnetism?
- Earth like large magnet that points N & S and gives us magnetic poles.
- When lava cools and solidifies, magnetic minerals align with N & S poles.
- Magnetic signatures are permanent and record movement of tectonic plates over time.
- Earth’s magnetic field “reverses” every 250k(avg). Where north becomes south & vice versa.
How are magnetic reversals recorded in some rocks?
Some rocks are magnetic and when they are formed the crystals align with the magnetic north.
how are magnetic reversals recorded in oceanic lithosphere important?
- polarity mirrored image on either side of mor.
- can tell you how fast the mor is forming new rocks. also how old rocks are and how long each magnetic reversal lasted.
How does plate tectonics affect the distribution of life on earth?
- ) geographic barriers.
2. )climatic barriers.
What are geographic barriers?
continents break apart and create new habitats. Increases diversity of species. Barriers can form or disappear.
what are examples of geographic barriers?
1.)Pangaea break-up, isthmus of panama.
what are climate barriers?
Locations of mountains, valleys, oceans, etc. control local climate and therefore distribution of critters.
what is an example of a climate barrier?
atacama desert in s. america. the driest place on earth because the mountais and coastal winds prevent rain.
what is a mineral?
it is naturally occurring, solid, has a lattice.
what is a lattice?
repeating 3d arrangement of atoms/molecules.
what are the mineral classes?
- )silicates:most diverse and common group. all contain silicone and oxigen. ex: zircon, quartz, opal.
- )carbonates:all contain carbon and oxygen. ex:calcite
- )halides:salts that contain chlorine, fluorine, or iodine. ex:table salt(halite), fluorite.
What are rocks …?
accumulations of 1 or more minerals
what are the three main types of rocks?
- igneous
- sedimentary
- metamorphic
igneous rocks are cooled and crystallized from what?
-melted rock.
Is lava above or below ground?
Above! Magma is below ground! Both are associated with volcanoes!
What controls crystal size in igneous rocks?
-The rate of cooling controls the crystal size and tells you where it cooled.
Do fine grained igneous rocks have small or large crystals?
-Small crystals
If crystals are small in fine-grained igneous rocks, then that means the rate of cooling was….?
-slow
Fine-grained igneous rocks with small crystals cooled down _____ ground.
-Above! Most likely erupted out of a volcano.
What size of crystals do coarse-grained igneous rocks have?
-Large
If crystals are large in coarse-grained igneous rocks, then that mean the rate of cooling of the rock was….?
-slow
Coarse-grained igneous rocks with large crystals cooled down ______ ground.
-below! Most likely was part of what used to be part of a magma chamber.
Do glassy igneous rocks have crystals, if so, what size?
No crystals!
For an igneous rock to be glassy with no crystals, then the rate of cooling must have been…?
-Fast! And cooled above ground. Most likely erupted out of a volcano.
What are some examples of igneous rocks?
- Peridotite (forms deep in Earth’s mantle)
- Basalt (is underlying rock in ocean basins)
- Granite (makes bulk of continent)
What are sedimentary rocks?
-rocks formed from sediments.
What are sediments?
-bits and pieces of other rocks and/or organic materials.
What are some examples of what sedimentary rocks could be made up of?
- Mud
- sand
- gravel
- leaves
- etc
Where do sedimentary rocks come from?
- weathering (chemical and physical breakdown by wind, water.)
- transportation (movement of seds by wind, water)
- deposition (being deposited on beaches, rivers, floodplains, ocean, etc.)
What are sedimentary rocks used for?
- To deconstruct Earth’s history!!!
- they indicate past environment of deposition.
- almost all fossils are found in sed rocks!
What are metamorphic rocks?
- Rocks changed under high temperatures and pressure.
- primarily due to burial
- leads to changes in physical or chemical composition.
- They are cooked but not melted
- Can happen to any rock type.
What are the two types of sedimentary rocks?
detrital and chemical
what are detrital rocks?
from consolidation of fragments (clasts or grains) of pre-existing rocks and/or organic material. mud, sand, gravel, etc…
what are chemical rocks?
material precipitates from fluids
- ) from dissolved minerals in water or
- ) through geological processes (critters) for example chalk.
what does it mean when a rock has big grain sizes?
high energy environment ex. river
small grain size?
low energy environment ex. lake
sedimentary structures:
sedimentary rocks commonly occur in layers. strata (beds) and have bedding planes.
strata beds=
layers like pages in a book. pgs can vary in thickness.
bedding planes=
horizontal surfaces between strata.
uncomformity =
time gap
how does seasonal variation affect sedimentary structures?
abrubt changes in the strata can mean abrupt environmental changes. gradual change can mean gradual environmental change. ex. seasonal variation big grain=> small grain.
cross bedding
internal multi order layering
ex. lg scale: wind deposition like sand dunes.
small scale:water deposition like rivers, streams.
saltation
Abrupt evolutionary change; sudden large-scale mutation.
The movement of hard particles over an uneven surface in a turbulent flow of air or water.
ripple marks
undulations on bedding planes. can be caused by movement of water or wind. back and forth (symmetrical)=open ocean unidirectional (asymmetrical)=river
bioturbation
the displacement and mixing of sediment particles…ex. barrows, trackways. destroys other sedimentary structures.
depositional environments
continental, transitional, marine.
continental depositional environments
FLUVIAL(river):*braided streams(high elevation)
-gravel
-cross-bedding sands
*meandering streams(low elevation)
-muds
-sands
DESERTS: *dunes- large cross-bedding
*alluvial fans- fan shaped at base of cliffs
- layered gravels, sands
GLACIAL: *moraines- material bulldozed by glacier. (different particle sizes)
*varves-fine laminations from seasonal lake sedimentation. can have dropped stones in it. think of glaciers as a solid flowing river.
transitional depositional environments
DELTAS:triangle shaped deposits where river mouth meets ocean.
-layered sands, mud
marine depositional environments
SHALLOW:continental shelf, slope & rise
turbudites can occur here.
turbudites=
underwater landslides (alluvial fan underwater) muds, fossils, bioturbation on continental shelf.
What are the types of fossilization? Explain.
- Permineralization (cavities/pores filled with minerals. It retains original material)
- Replacement (existing hard parts replaced by other minerals. Ex. opalized ammonite)
- Mold (-) and Cast (+) [counterparts]
- Carbonization (organic matter –> thin residue of carbon)
- Amber (fossilized tree sap ; entire organism may be preserved.
