EarthSci (Midterm 2024) Flashcards
What is our current understanding of how the solar system formed? What is the evidence?
4.5 billion years ago, dense cloud of gas and dust collapsed, caused by shockwave from nearby supernova. Created solar nebula. At centre, hydrogen atoms combined to form helium, releasing energy and creating the sun. Matter aggregated to form large bodies. Took 50 million years. Evidence: samples from planets have similar age. Suggests that planet formation is regular after star collapse.
How do we get information about planetary age and composition?
Sampling (planet/meteorites). Using radiometric dating on samples
Discuss formation of the Earth.
Large planets take millions of years to form. Around 4.5 - 4.6 billion years ago, dust and gas aggregated around a young sun. Collisions helped it grow in size.
Discuss formation of the Moon.
Giant impact theory: proto-planet (Theia) hit earth 4.45 billion years ago. Ejected mass from impact formed the moon. Atmosphere thinned, Earth’s core solidified and cooled.
How are other planets different from Earth?
Mercury, Venus, Mars: terrestrial planets (just like earth). Developed as hot rocky masses. Underwent differentiation.
Saturn/Jupiter: gas giants (no solid surface)
Define differentiation.
Dense mass goes towards centre, creating layers in the planetary surface,
Discuss the internal structure of the earth.
Core: radius of 3500 km, liquid nickel/iron
Mantle: radius of 2900 km, igneous (silicate) rock
Crust: oceanic (thin, denser, basalt) and continental (thick, granite)
What is the evidence of earth’s composition?
- earth materials (eg. diamonds give info about mantle, most are 3.3 bya and formed at 1500°C)
- Seismic waves (reflection/refraction, waves bend towards lower density materials)
- Drilling
What is Mohorovičić discontinuity?
Boundary between crust and mantle
What is the Lithoprobe?
Canadian project using seismic waves, investigating composition of the Canadian Shield.
How do we date geological material/events?
Carbon dating: for things less than 20,000 y.o.
Radiometric dating: half-life dating
Surface exposure dating: measuring isotopes on surface of a sample, discovering when object was last covered by ice.
What are the assumptions made when doing radiometric dating?
Parent element will always decompose into daughter element.
What are the best isotope(s) for radiometric dating? Why?
Potassium-40. Good because it decays into argon, a gas, meaning it CANNOT escape after the sample is solidified. Also - extremely long half life (1.26 billion years). Useful for dating of magma and very old rocks.
What is a zircon?
Zircon is ZrSiO4, a hard and erosion-resistant material. One of the oldest dated on earth. Formed in igneous rocks like granite.
Who are the main scientists that proposed plate tectonic theory? What were their discoveries?
Alfred Wegener: continental drift theory. Proposed Pangea.
Harry Hess: introduced idea of the sea floor spread. Ridges —> new crust, trench —> old crust subducted.
What is an MOR?
Mid-ocean ridge. Sea floor mountain system caused by plate tectonics. Formation of sea floor occurs here, movement away from ridges.
How old is the sea floor? How do we know?
~340 million years (east Mediterranean Sea). Isotope dating, movement of sea floor towards this area.
What is paleomagnetism?
Study of the magnetic polarity of rocks. Samples can become polarized at the magnetic polarity of their origin, identical or opposite to current day. Record of strength and direction of magnetic field.
Describe the three types of plate boundaries.
Divergent margins: moving away. Creates new ocean basin/crust. Volcanism/shallow focus earthquakes.
Convergent margins: towards. Shallow to deep earthquakes. Deep trenches /island volcanoes.
Transform boundaries, sliding past. Shallow focus earthquakes
What is an earthquake?
Def.: motion or trembling of the ground caused by a sudden displacement of rock.
What are the three types of seismic waves?
P-waves (primary body): compressional, 4-7km/s, parallel to wave propagation
S-waves (secondary body):shear, 2-5 km/s, perp. To wave propagation, CANNOT travel through fluid
Surface: love waves (horizontal), and Rayleigh waves (rolling/destructive)
What is the epicentre of an earthquake.
Point on earth’s surface directly ABOVE focus (point of initial movement)
Can we predict earthquakes in Hamilton?
Close to old suture line in shield (central metasedimentary belt boundary zone), and N. American plate moving westward. Possible future stresses causing earthquakes.
How do we determine the size of an earthquake?
Measure how much damage is caused (human-focussed). Intensity of the earthquake.
Describe the two types of seismometers
Seismograph: records motion, global network of stations.
Seismogram: paper record on which P and S waves are differentiated.
What are the three main layers of the Earth?
Core (inner solid, outer liquid), Mantle, Crust.
What is the Moho discontinuity?
The boundary between the Earth’s crust and mantle.
What are seismic waves and how do they help understand Earth’s structure?
Seismic waves (P-waves and S-waves) travel through Earth’s layers and bend at boundaries, revealing details about the composition and state of the layers.
What is radiometric dating?
A method of dating rocks by measuring the decay of radioactive isotopes into stable daughter products.
What is the half-life of 238U?
4.5 billion years.
Why are zircons important for dating rocks?
Zircons contain trace amounts of uranium, resist erosion, and provide accurate dates using uranium-lead techniques.
What are the three main types of plate boundaries?
Divergent, Convergent, Transform.
What evidence supports plate tectonic theory?
Mid-ocean ridges, sea floor spreading, magnetic reversals, and matching fossils/rock formations across continents.
What is paleomagnetism?
The study of the record of Earth’s magnetic field in rocks, which has validated the theory of plate tectonics through magnetic reversals.
What are the types of seismic waves and their properties?
P-waves (compressional, fast), S-waves (shear, slower, cannot pass through liquids), Surface waves (cause the most damage).
How is an earthquake’s epicenter located?
By using data from three or more seismic stations to triangulate the location.
What hazards are caused by earthquakes?
Ground shaking, tsunamis, liquefaction, landslides.
What are the two primary ways to measure the size of an earthquake?
Richter Scale (based on amplitude of seismic waves), Moment Magnitude Scale (based on energy released).
What is a mid-ocean ridge?
A mountain range on the ocean floor where new oceanic crust is formed by volcanic activity.
Example sentence: The Mid-Atlantic Ridge is a well-known mid-ocean ridge.
What evidence did paleomagnetism provide for plate tectonics?
The symmetrical patterns of magnetic reversals on either side of mid-ocean ridges confirm that plates are moving apart over time.
How does the Moment Magnitude Scale differ from the Richter Scale?
The Moment Magnitude Scale measures the total energy released during an earthquake, while the Richter Scale measures the amplitude of seismic waves.
What is a travel-time curve used for?
It’s used to calculate the distance between a seismograph and the earthquake’s epicenter based on the arrival times of P-waves and S-waves.
What is the Modified Mercalli Intensity (MMI) scale?
A scale that measures the intensity of ground shaking during an earthquake, ranging from I (not felt) to XII (total destruction).
What is the asthenosphere, and how does it relate to the lithosphere?
The asthenosphere is the semi-fluid layer beneath the lithosphere, allowing tectonic plates to move.
How does seismic refraction provide evidence for Earth’s internal structure?
Seismic waves bend as they travel through materials of different densities, helping scientists infer the composition of Earth’s layers.
What is the significance of half-life in radiometric dating?
It is the time required for half of a radioactive isotope to decay, providing a measure for determining the age of rocks.
Why is 40K-40Ar dating used, and what materials is it best for?
Potassium-Argon dating is used because of its long half-life and the abundance of 40K in minerals like micas and feldspars. It’s best for dating volcanic rocks.
What is the significance of the Pacific Ring of Fire?
It is a zone of frequent earthquakes and volcanic activity encircling the Pacific Ocean, associated with convergent boundaries.
What is the difference between ocean-ocean convergence and ocean-continent convergence?
In ocean-ocean convergence, one oceanic plate subducts beneath another, forming volcanic island arcs. In ocean-continent convergence, the oceanic plate subducts beneath the continental plate, forming mountain ranges and volcanic activity.
How do pillow lavas form at divergent boundaries?
Pillow lavas form when basaltic lava erupts underwater and rapidly cools, creating rounded, pillow-like structures.
What is elastic rebound theory in relation to earthquakes?
Elastic rebound theory explains that stress builds up in rocks along a fault until it exceeds the rock’s strength, causing the rocks to break and release energy as seismic waves.
How are tsunamis generated by earthquakes?
Tsunamis are caused by the sudden displacement of the sea floor during an earthquake, which creates large, fast-moving waves.
What areas of Canada are at risk from earthquakes, and why?
Areas along the west coast, such as British Columbia, are at risk due to the proximity to the Pacific Plate and the Cascadia subduction zone.
Why is radiometric dating not useful for all rock types?
It is not useful for sedimentary rocks because they are made from fragments of other rocks, which can give mixed age signals.
What is the significance of the fission track dating technique?
It measures damage trails left by the spontaneous fission of uranium-238 atoms in minerals like zircon, providing an age estimate for the mineral’s formation.
What is LITHOPROBE, and why is it important?
LITHOPROBE is a Canadian multidisciplinary project that investigates the structure and composition of the Earth’s crust using seismic data and geological fieldwork.
What are kimberlite pipes, and what is their significance in understanding Earth’s mantle?
Kimberlite pipes are volcanic features that bring material from deep in the mantle to the surface, often containing diamonds, providing insights into deep Earth conditions.
