EarthSci (Midterm 2024)

Question 1

What is our current understanding of how the solar system formed? What is the evidence?

Answer 1

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.

Question 2

How do we get information about planetary age and composition?

Answer 2

Sampling (planet/meteorites). Using radiometric dating on samples

Question 3

Discuss formation of the Earth.

Answer 3

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.

Question 4

Discuss formation of the Moon.

Answer 4

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.

Question 5

How are other planets different from Earth?

Answer 5

Mercury, Venus, Mars: terrestrial planets (just like earth). Developed as hot rocky masses. Underwent differentiation.
Saturn/Jupiter: gas giants (no solid surface)

Question 6

Define differentiation.

Answer 6

Dense mass goes towards centre, creating layers in the planetary surface,

Question 7

Discuss the internal structure of the earth.

Answer 7

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)

Question 8

What is the evidence of earth’s composition?

Answer 8

1. earth materials (eg. diamonds give info about mantle, most are 3.3 bya and formed at 1500°C)
2. Seismic waves (reflection/refraction, waves bend towards lower density materials)
3. Drilling

Question 9

What is Mohorovičić discontinuity?

Answer 9

Boundary between crust and mantle

Question 10

What is the Lithoprobe?

Answer 10

Canadian project using seismic waves, investigating composition of the Canadian Shield.

Question 11

How do we date geological material/events?

Answer 11

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.

Question 12

What are the assumptions made when doing radiometric dating?

Answer 12

Parent element will always decompose into daughter element.

Question 13

What are the best isotope(s) for radiometric dating? Why?

Answer 13

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.

Question 14

What is a zircon?

Answer 14

Zircon is ZrSiO4, a hard and erosion-resistant material. One of the oldest dated on earth. Formed in igneous rocks like granite.

Question 15

Who are the main scientists that proposed plate tectonic theory? What were their discoveries?

Answer 15

Alfred Wegener: continental drift theory. Proposed Pangea.
Harry Hess: introduced idea of the sea floor spread. Ridges —> new crust, trench —> old crust subducted.

Question 16

What is an MOR?

Answer 16

Mid-ocean ridge. Sea floor mountain system caused by plate tectonics. Formation of sea floor occurs here, movement away from ridges.

Question 17

How old is the sea floor? How do we know?

Answer 17

~340 million years (east Mediterranean Sea). Isotope dating, movement of sea floor towards this area.

Question 18

What is paleomagnetism?

Answer 18

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.

Question 19

Describe the three types of plate boundaries.

Answer 19

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

Question 20

What is an earthquake?

Answer 20

Def.: motion or trembling of the ground caused by a sudden displacement of rock.

Question 21

What are the three types of seismic waves?

Answer 21

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)

Question 22

What is the epicentre of an earthquake.

Answer 22

Point on earth’s surface directly ABOVE focus (point of initial movement)

Question 23

Can we predict earthquakes in Hamilton?

Answer 23

Close to old suture line in shield (central metasedimentary belt boundary zone), and N. American plate moving westward. Possible future stresses causing earthquakes.

Question 24

How do we determine the size of an earthquake?

Answer 24

Measure how much damage is caused (human-focussed). Intensity of the earthquake.

Question 25

Describe the two types of seismometers

Answer 25

Seismograph: records motion, global network of stations. Seismogram: paper record on which P and S waves are differentiated.

Question 26

What are the three main layers of the Earth?

Answer 26

Core (inner solid, outer liquid), Mantle, Crust.

Question 27

What is the Moho discontinuity?

Answer 27

The boundary between the Earth's crust and mantle.

Question 28

What are seismic waves and how do they help understand Earth's structure?

Answer 28

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.

Question 29

What is radiometric dating?

Answer 29

A method of dating rocks by measuring the decay of radioactive isotopes into stable daughter products.

Question 30

What is the half-life of 238U?

Answer 30

4.5 billion years.

Question 31

Why are zircons important for dating rocks?

Answer 31

Zircons contain trace amounts of uranium, resist erosion, and provide accurate dates using uranium-lead techniques.

Question 32

What are the three main types of plate boundaries?

Answer 32

Divergent, Convergent, Transform.

Question 33

What evidence supports plate tectonic theory?

Answer 33

Mid-ocean ridges, sea floor spreading, magnetic reversals, and matching fossils/rock formations across continents.

Question 34

What is paleomagnetism?

Answer 34

The study of the record of Earth’s magnetic field in rocks, which has validated the theory of plate tectonics through magnetic reversals.

Question 35

What are the types of seismic waves and their properties?

Answer 35

P-waves (compressional, fast), S-waves (shear, slower, cannot pass through liquids), Surface waves (cause the most damage).

Question 36

How is an earthquake’s epicenter located?

Answer 36

By using data from three or more seismic stations to triangulate the location.

Question 37

What hazards are caused by earthquakes?

Answer 37

Ground shaking, tsunamis, liquefaction, landslides.

Question 38

What are the two primary ways to measure the size of an earthquake?

Answer 38

Richter Scale (based on amplitude of seismic waves), Moment Magnitude Scale (based on energy released).

Question 39

What is a mid-ocean ridge?

Answer 39

A mountain range on the ocean floor where new oceanic crust is formed by volcanic activity. ## Footnote Example sentence: The Mid-Atlantic Ridge is a well-known mid-ocean ridge.

Question 40

What evidence did paleomagnetism provide for plate tectonics?

Answer 40

The symmetrical patterns of magnetic reversals on either side of mid-ocean ridges confirm that plates are moving apart over time.

Question 41

How does the Moment Magnitude Scale differ from the Richter Scale?

Answer 41

The Moment Magnitude Scale measures the total energy released during an earthquake, while the Richter Scale measures the amplitude of seismic waves.

Question 42

What is a travel-time curve used for?

Answer 42

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.

Question 43

What is the Modified Mercalli Intensity (MMI) scale?

Answer 43

A scale that measures the intensity of ground shaking during an earthquake, ranging from I (not felt) to XII (total destruction).

Question 44

What is the asthenosphere, and how does it relate to the lithosphere?

Answer 44

The asthenosphere is the semi-fluid layer beneath the lithosphere, allowing tectonic plates to move.

Question 45

How does seismic refraction provide evidence for Earth’s internal structure?

Answer 45

Seismic waves bend as they travel through materials of different densities, helping scientists infer the composition of Earth’s layers.

Question 46

What is the significance of half-life in radiometric dating?

Answer 46

It is the time required for half of a radioactive isotope to decay, providing a measure for determining the age of rocks.

Question 47

Why is 40K-40Ar dating used, and what materials is it best for?

Answer 47

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.

Question 48

What is the significance of the Pacific Ring of Fire?

Answer 48

It is a zone of frequent earthquakes and volcanic activity encircling the Pacific Ocean, associated with convergent boundaries.

Question 49

What is the difference between ocean-ocean convergence and ocean-continent convergence?

Answer 49

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.

Question 50

How do pillow lavas form at divergent boundaries?

Answer 50

Pillow lavas form when basaltic lava erupts underwater and rapidly cools, creating rounded, pillow-like structures.

Question 51

What is elastic rebound theory in relation to earthquakes?

Answer 51

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.

Question 52

How are tsunamis generated by earthquakes?

Answer 52

Tsunamis are caused by the sudden displacement of the sea floor during an earthquake, which creates large, fast-moving waves.

Question 53

What areas of Canada are at risk from earthquakes, and why?

Answer 53

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.

Question 54

Why is radiometric dating not useful for all rock types?

Answer 54

It is not useful for sedimentary rocks because they are made from fragments of other rocks, which can give mixed age signals.

Question 55

What is the significance of the fission track dating technique?

Answer 55

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.

Question 56

What is LITHOPROBE, and why is it important?

Answer 56

LITHOPROBE is a Canadian multidisciplinary project that investigates the structure and composition of the Earth’s crust using seismic data and geological fieldwork.

Question 57

What are kimberlite pipes, and what is their significance in understanding Earth’s mantle?

Answer 57

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.