Geology Exam 1
What were the two main heat sources for early Earth?
Radioactive decay & collisions from asteroids
Describe the four lines of evidence that Wegener gathered to support the continental drift hypothesis.
- Continents are like a jigsaw puzzle and fit together. - Fossils matching across multiple continents. - Matching geological features like mountain ranges, etc. -Matching Climate Zones
What is the scientifically accepted age of the Earth?
4.6 billi years
Who is credited with developing the continental drift hypothesis?
Alfred Wegner
What are the two types of natural resources? Give examples for each type.
Biotic: Anything from a living organism (i.e. coal, oil) Abiotic: anything non-organic (water, air, metals)
How is cleavage different from fracture?
Cleavage is smooth breaks because of weak bonding, while fractures are irregular breaks due to strong bonding.
Compare a continental volcanic arc and a volcanic island arc.
Continental happens with oceanic-continental, creating volcanoes on land, volcanic island arc is oceanic-oceanic creating a line of volcanic islands.
Briefly describe how mountain systems like the Himalayas are formed.
Continental-continental convergent boundaries are pushed together because neither plate is more dense so they squish together creating mountain ranges.
List at least three different lines of evidence that Wegener gathered to support the continental drift hypothesis.
Continents fit together like jigsaw, fossils of animals matching across continents, geographical features like mountain ranges matching across continents
List and briefly describe Earth's compositional divisions.
Crust, Mantle, Core
What is seafloor spreading? Where is active seafloor spreading occurring today?
Divergent plate boundaries spread apart on the seafloor, creating new crust. currently occurring on the mid-oceanic ridge, the longest chain of mountains mostly underwater.
List the three types of plate boundaries and describe the relative motion at each of them.
Divergent: plates move apart creating new lithosphere/crust, Convergent: plates collide and the older one is subducted into the mantle and recycled, Transform: plates slide horizontally and cause earhtquakes
What are the most significant natural hazards in our San Francisco Bay Area?
Earthquakes
What are the two most abundant minerals in the continental crust?
Feldspar (plagioclase, then potassium) and quartz
How do light-colored igneous rocks differ in composition from dark-colored igneous rocks?
Felsic = heavily feldspar & silica, Mafic = heavily iron & magnesium
List the four basic compositional groups of igneous rocks, in order from highest silica content to lowest silica content.
Felsic, intermediate, mafic, ultramafic
What is the primary focus of this course, physical geology?
Geology is the science of understanding planet earth. Physical Geology examines materials composing Earth and seeks to understand the many processes that operate on our planet
Explain the differences between ionic, covalent and metallic bonding.
Ionic: transfer of electrons, covalent: sharing of electrons (strongest), Metallic: electrons move freely.
Describe the processes that led to earth's iron-rich core.
Iron and heavier metals are more dense and sunk deeper into the earth, while the more buoyant elements rose to the crust
Why does oceanic lithosphere subduct while continental lithosphere does not?
It is older, and more dense
How does lava differ from magma?
Lava = above ground, Magma = below ground
Compare and contrast the lithosphere and the asthenosphere.
Lithosphere is the crust & upper mantle w/ rigid rocks, Asthenosphere is under the litho and rocks move much more fluidly.
What is a mantle plume? What is a hot spot volcanism?
Mantle plums are fixed locations in the mantle where magma rises, they seem to change because the tectonic plates on the crust shift. hotspots are the areas where these plums rise too, ex: hawaii, iceland, yellowstone.
What is a mineral? List five characteristics of a mineral.
Minerals are the building blocks of earth · Naturally Occurring · Inorganic · Solid · Definite Chemical Composition (chemical formula ex SiO2 is quartz) · Ordered atomic crystal structure
Where does new lithosphere form? Where is it consumed?
New litho formed at divergent plate boundaries at the spreading center when lava is cooled. Consumed at convergent plate boundaries when the older plate is sub-ducted into the asthenosphere.
Briefly explain why middle of the ocean is not the deepest part of the ocean.
Oceanic trenches are created at convergent boundaries. older crust spreads away from divergent boundaries.
What are the three types of convergent plate boundaries?
Oceanic-Continental, Oceanic-Oceanic, Continental-Continental. The more dense plate (oceanic) is subducted and can create continental volcanic arcs, forming volcanic islands. Continental-continental where neither plate is more dense has them push together and create mountain ranges (i.e. Himalayas)
What is partial melting?
Partial melting is the incomplete melting of rocks. This process produces most magmas. Rising magma partially melts resulting in felsic magma and mafic residue containing olivine, pyroxene, etc. the process of creating felsic magma.
texture of igneous rocks that are ejected from volcanos
Phaneritic
Describe three ways a mineral might form (crystallize).
Precipitation, Cooling/crystalization, deposition/biological process.
Natural resources include both renewables and non-renewables. Give an example for each.
Renewable: water or soil, Non: fossil fuels or metals
Describe slab pull and ridge push. Which of these forces appears to contribute the more to plate motion?
Ridge Push: the motion of plates being pushed along divergent boundaries, Slab pull: the motion of a plate being sub-ducted and the weight of the other plate pulling it into the mantle. slab pull contributes more.
The early Earth separated into different layers as a result of differentiation. What are the three basic layers of the interior of the Earth?
The Crust, Mantle, and Core
What is the nebular theory?
The birth of our solar system began as a cloud (nebula) of dust and gases that started to collapse under its own gravitation.
Geology is traditionally divided into two broad areas - physical and historical geology. What is the primary focus of this course, physical geology?
The primary focus of this course is Physical Geology, which examines materials that make up Earth and understanding the process of the origin of earth and its development through time
How do increasing population and urban sprawl make people more vulnerable to natural disaster?
These are natural hazards, but can become natural disasters when around large populations of people
On what basis are minerals placed in mineral classes?
They are classified by the dominant portion of their chemical composition
What is continental rifting? Where can we see this process occurring today?
When divergent plate boundaries separate and spread on land. currently happening in the east african rift
Describe decompression melting.
When hot magma rises to a weak point in the mantle/crust it lowers in pressure, cooling the magma.
Why are rocks of intermediate (andesitic) and felsic (granitic) composition generally not found in the ocean basins?
basaltic magma forms at the great depths of ocean basins. the magma never goes through the partial melting process to become intermediate/felsic
What are the two criteria geologists use to classify igneous rocks?
composition: chemical/mineral makeup, and texture: coarse or fine grained, shows cooling history
What are the three different ways that magma can be generated?
decompression (lowering pressure), addition of water (lowers melting temp), heat transfer (deeper magma melts wall rock creating more magma)
How does the rate of cooling influence the texture of igneous rocks?
extrusive cools rapidly with non-visible crystals, intrusive cools slowly with larger crystals.
Compare and contrast extrusive and intrusive igneous rocks.
extrusive is formed by cooled lava, intrusive is formed by cooled magma under ground.
Describe the doctrine of uniformitarianism.
is the physical, chemical, and biologic laws that operate today have always operated throughout the geological past. Present geology is the key to interpreting what happened in the past.
What is magmatic differentiation? How might this process lead to the formation of several different igneous rocks from a single magma?
it is the process that occurs when magma cools underground and solidifies, and how magma can be made up of different compostions (felsic/mafic).
What is heat-transfer melting and where does it occur?
it occurs when deeper magma melts the wall rock, creating new magma. the deeper the magma the higher the pressure and the hotter it is.
What does a porphyritic texture indicate about an igneous rock?
it was cooled at 2 different times, extrusivley and intrusivley
Describe a simple chemical test that is useful in identifying the mineral calcite.
its effervescence: reaction to acids
Why might it be difficult to identify a mineral by its color?
minerals can come in many different colors, and small chemical imbalances can change the color of a mineral.
Earth went through a time of intense heating when it was first formed and became hot enough to melt iron and nickel. What were the two main sources for the increased temperature during this time?
radioactive decay and collisions from asteroids
How do we determine hardness of a mineral?
resistance to scratching
What are polymorphs?
same chemical composition, but atomic structure is different forming a different mineral.
What is the most common mineral group and why is it important?
silicates, makes up 90% of minerals on earth
Why was the continental drift hypothesis rejected in the scientific community when it was first proposed?
the actual forces generated by the rotation of the earth were calculated to be insufficient to move continents.
How does the introduction of volatiles trigger melting?
the addition of volatiles like water lowers the melting point, making it take less heat to crystallize
What is the oceanic ridge system?
the longest mountain range in the world, it is under water and is in every ocean in the world.
What is the country rock or host rock?
the native rock, that is older and there before the magma comes in.
In what tectonic setting are most basaltic magmas generated?
they are created in the mantle, slightly past their melting temperature.