Ch. 01 Flashcards
Define Geology
Geology focuses on Earth, its rocks, processes shaping it, and surface modeling.
This branch of science focuses on Earth, its rocks, processes shaping it, and surface modeling.
Geology
What kind of changes occurs on earth are observable for ex. erosion which affects coastlines and continental heights?
Surface Changes
This type of changes on earth involve slow continent movements, volcanic erruptions, and earthquakes.
Subsurface Changes
What type of energy transactions influence geological processes?
Solar energy, geothermal heat loss, and seismic energy release/earthquake
What impacts engineering at rates comparable to comon practices?
Geological effects
What serves as earths history books, preserving events and remains of living organisms?
Rocks
What are the tree major rock groups?
igneous, sedimentary, and metamorphic
It is composed of minerals, forming a mechanical basis of geological materials in engineering.
rocks
How do you differentite rocks from soils?
Rock - denotes hard materials
soil - refers to sediments or granular residues
they can be differentiated from their sizes using a sieve.
_______ & _______ contains pores and fissures filled with liquidor gas.
rocks and soils
By how much shorter is the earth’s polar radius from its equitorial radius? and why is that?
22km, this makes the earth’s shape slightly oblate due to its rotation and the centrifugal force.
Approximately, what percentage of earth is land?
29%, almost 35% including continental shelves
What part of the earth cover about two-thirds of the earth’s surface?
the Oceans
What is the average land height?
0.86 km above sea level
what is the mean ocean floor depth?
about 3.8 km
True or False: Extremes in height and depth are limited and small compared to Earth’s radius
TRUE
What is composed of oceans, seas, lakes, and rivers, collectively?
the hydrosphere
The Earth is surrounded by a gaseous envelope called?
the atmosphere
What advanced measurement techniques revealed detailed ocean floor surveys?
seismic refraction
What are the continental margin features?
continental shelf (gentle slope), shelf break, continental slope, and continental rise.
What plain is reached below 2700 fanthoms (5km) ?
The deep abyssal plain
This hosts submarine volcanic islands and drowned peaks related to oceanic ridges.
Abyssal plain
It is a submerged extension of land with a gentle slope
Continental shelf
It is marked change in slope leading to the continental slope.
Shelf break
continental slope transitions to the continental rise with a _______
diminishing gradient
Volcanoes rising from the abyssal plain may form ________
sea mounts
Volcanoes no longer breaking the earth’s surface are called
sea mounts
These are sumbarine chains of mountains rising 2 to 4 km above the ocean floor
Oceanic ridges
What defines the base of the lithosphere?
at 30km depth, rocks could begin to melt and temperature increases downward at an average of 30 deg per km
What is the earth’s core made of ?
a mixture of iron and nickel
What surrounds the earth’s core?
Mantle
What is the thickness of the earth’s crust?
in continental areas, 30 km
in oceans, 10 km
What do seismic studies use to gain insights into Earth’s interior structure?
a) Magnetic fields
b) Elastic waves from earthquakes
c) Gravity measurements
d) Atmospheric pressure
b) Elastic waves from earthquakes
What is the approximate density of Earth’s core as revealed by seismic studies?
8
Where are earthquake centers mainly located, according to seismic studies?
In two surface belts, one around the Pacific and the other from Europe to Asia
What causes earthquakes?
Fractures (faults) relieving stress in crustal rocks
What can serve as precursors to earthquakes?
Changes in land shape, water levels, and seismic activity
How do earthquakes vary in intensity?
From slight tremors to severe shocks causing various damages
How can the impact of earthquakes be mitigated in affected areas?
Through earthquake-resistant structures and designs
What phenomenon can result from rapid changes in ocean floor elevation during sea earthquakes?
Tsunamis
Where are earthquake centers primarily concentrated globally?
Along two belts: the circum-Pacific belt (75%) and the Alpine area (22%)
What is used to estimate earthquake intensity, and what is the scale’s range?
Mercalli Scale; I to XII
What do isoseismal maps mark during an earthquake?
a) Points of equal temperature
b) Points of equal intensity
c) Points of equal air pressure
d) Points of equal humidity
b) Points of equal intensity
How is seismic energy release measured during an earthquake?
Magnitude (M) on Richter’s logarithmic scale
What does the magnitude (M) of an earthquake correlate with?
Seismic energy
What is the approximate threshold for an earthquake to be considered a major disaster in terms of magnitude (M)?
M=7
How are the Richter Scale and the Mercalli Scale related?
They are not directly comparable, but M=5 roughly corresponds to Grade VI on the Mercalli Scale
What type of waves do earthquakes generate that propagate from the focus to the epicenter?
Seismic waves
What are the primary types of seismic waves?
Primary (P) and Secondary (S) waves
How do seismographs record vibrations during an earthquake?
With a pivoted beam carrying a mass
What is the shadow zone in the context of seismic waves?
An area where P and S waves do not arrive
What does the Mohorovicic discontinuity (Moho) mark in Earth’s interior?
Crust-mantle boundary
How is crustal structure determined using seismic waves?
By observing waves traveling through crustal rocks
What is the average thickness of continental crust?
30 km
what does the Earth’s outer lithosphere rest on?
Upper mantle
What is indicated by vertical and horizontal lithospheric movements ?
Continental drift and plate tectonics
What geological concept unifies isostacy and continental drift ?
Plate Tectonics
What does the term isostacy refer to in the context of Earth’s crust?
The balance between continental masses and underlying sub-crustal material
How is isostatic balance tested?
gravity surveys
What is the primary role of the asthenosphere in isostatic adjustment?
Facilitating slow upward movements during denudation
How did the Earth’s height, particularly in areas like the Himalayas, maintain during isostatic adjustment?
denudation involving the removal of significant rock quantities
What geological event during the Glacial epoch caused the depression of land areas
Thick ice-sheets
What is the estimated rate of Earth’s expansion?
1 cm per year
According to the Earth’s expansion hypothesis, what might explain the inconsistencies in paleomagnetism?
Earth’s slow expansion
What is the primary driving force behind the mechanism of continental drift?
Mantle convection currents
What is the state of balance maintained in isostasy called?
Level of compensation
Define asthenosphere in the context of Earth’s structure
Weak layer beneath the lithosphere.
What role does the asthenosphere play in isostatic adjustment during denudation?
Facilitates slow rise of the surface, lightening it.
Who proposed the concept of continental drift, and in which year
Alfred Wegener in 1912.
Why was Wegener’s continental drift idea initially met with controversy?
Lack of supporting evidence.
What evidence did Wegener use to support continental drift?
Similar coastlines, geological features, and fossil faunas.
According to A.L. du Toit, what demonstrated an accurate fit between continents?
Fit between Africa and South America at their continental shelves.
What does rotational change refer to in the context of continental drift?
Changes in the position and orientation of continents.
Give an example of a shared feature supporting past adjacency between continents.
Similar mountain ranges between North America and Europe.
Around how many million years ago did Gondwanaland exist, according to the text?
400 million years ago.
What evidence suggests a shared glaciation event in Gondwanaland?
Glacial deposits in southern Africa, India, Australia, Brazil, and Argentina.
Approximately how long ago did Africa and India move northwards and collide with Eurasia?
200 million years ago.
What is observed between drifting continents?
Oceanic ridges.
What structures resemble submerged mountain ranges found in all oceans?
Oceanic ridges.
What extends along the summit of the mid-Atlantic Ridge?
Median rift.
What process is indicated by radiometric dating of basalts in oceanic ridges?
Ocean floor spreading.
What is involved in ocean floor spreading?
Lateral movement of volcanic material creating new ocean floor.
What type of rocks provide independent evidence for ocean floor spreading and continental drift?
Basaltic rocks.
Which mineral with magnetic properties is found in basaltic rocks?
Magnetite.
What term is used for retained magnetic properties in rocks, revealing changes in their position over time?
Palaeomagnetism or fossil magnetism.
What pattern is observed on basaltic rocks on oceanic ridges, such as the North Atlantic Ridge?
Striped pattern parallel to the median rift.
What does alternate striping of reversed magnetism on basaltic rocks indicate?
Periodic reversals of Earth’s magnetic poles.
How is the dating of magnetic stripes on the ocean floor accomplished?
Radiometric dating.
When did the last reversal of Earth’s magnetic field occur?
About 700,000 years ago.
What does the increasing age of basaltic rocks with distance from the median rift indicate?
Duration of ocean floor spreading.
What is the estimated present rate of ocean floor spreading?
Between 1 cm and 3 cm per year.
What distinguishes rocks near the center of oceanic ridges in terms of temperature?
They have higher temperatures compared to those on either side.
What drives the upward flow of material from the mantle in oceanic ridges?
Mantle convection currents.
What is the driving force behind the upward flow of material in oceanic ridges?
Buoyancy due to lower density in the rising current.
How are horizontal displacements accommodated in the mechanism of continental drift?
Through displacement on fractures called transcurrent faults.
What geological role do extensive fracture systems with horizontal displacements play?
They contribute to the Earth’s crust architecture.
Which major geological feature is formed where two continental plates converge?
Intercontinental fold mountain belts.
What does seismic data collected by a worldwide seismic network support?
Plate tectonics theory.
How is new sea-floor formed?
Oceanic Ridges
How is the destruction of oceanic crust balanced in the Earth’s crust?
Through subduction.
What emerged as a geological idea in the mid-1960s, considering the lithosphere as a mosaic of plates?
Plate tectonics.
What are the three types of plate movements mentioned in the text?
Sliding past each other, moving away from each other, and one sliding underneath the other.
Name a type of plate capped by continental crust, according to the text.
Continental Plates.
What concept suggests that the Earth is slowly expanding, increasing its surface area?
Earth’s Expansion Hypothesis.
What evidence does the Earth’s Expansion Hypothesis use to support its claims?
Palaeogeographical maps, astronomical evidence, and paleomagnetism inconsistencies.
What is the estimated rate of the Earth’s expansion according to the hypothesis?
0.24 mm per year, totaling about 20% in 4500 million years.
When did Earth and other Solar System bodies form?
Around 4600 million years ago.
What process led to the formation of the primitive Sun at the center of the Solar System?
Gradual contraction from a rotating, flattened cloud of gas and dust.
How did planets, including Earth, form?
From local condensations in the rotating cloud.
What initially characterized the primitive Earth before it gradually heated?
It was cold.
What factors contributed to the heating of the primitive Earth?
Compression and decay of radioactive materials.
What geological components formed due to the melting of the primitive Earth?
Core, mantle, and outer crust.
Approximately, when do the oldest discovered rocks on Earth date back to?
About 3900 million years.
When did the primitive crust likely form, and what type of crust was it?
Around 4400 to 4500 million years ago; likely basaltic.
What contributed to continent formation during the primitive crust’s evolution?
Separation of lighter (granitic) fluids after cracking and re-melting.
How did the early oceans on Earth form?
As the Earth’s surface cooled, water collected.
When is it suggested that the modern atmosphere likely formed?
Within the last 1000 million years.
What scientific method is used for modern estimates of rock ages?
Radiometric methods.
Who discovered radioactivity, enabling age calculations based on element transformations?
Pierre and Marie Curie.
Which radioactive transformation is useful for dating igneous rocks?
Potassium into argon.
Which radioactive transformation is useful for dating metamorphic rocks?
Rubidium into strontium.
What method is employed for dating materials like wood and plant remains for smaller ages?
Carbon-14 dating.
How are rocks classified into geological groups?
Based on their age.
Why is the geological history of rocks crucial for engineering purposes?
Understanding the mechanical character of rocks and soils.
What fraction of geological time is particularly important in engineering?
The last one-eighth.
What era represents approximately seven-eighths of geological history?
Precambrian Era.
How is the Precambrian Era described in terms of our knowledge?
Poorly known but essential for understanding Earth’s geological evolution.
