Chapter 7: Earth Flashcards
Are there any other planets that are capable of supporting Earth-like life in our Solar System?
No, currently Earth is the only one
What is the distance from Earth to the Sun? What number planet is it from the Sun.
- 1 AU or 150 million km
- The third planet from the Sun
Where does Earth rank in size in our Solar System?
Fifth largest planet
Where does Earth rank in density for planets in Solar System?
What is Earth’s density?
densest major body in the solar system
Earth density = 5.5g/cm^3
How many permanent satellites does Earth have?
one, the moon
How many degrees is Earth’s plane of orbit from the equatorial plane of the Sun?
7 degrees (quite a small inclination)
What is Earth’s angle of obliquity/tilt of rotational axis
23 degrees
What causes the Earth’s seasons?
The angle of obliquity/tilt of rotational axis. Changes which parts of Earth are exposed to the Sun at different parts of the year (different times in it’s orbit)
What is precession? What is the cause of Earth’s precession?
Precession is a movement of Earth’s axis that resembles a spinning top wobbling as it spins. Instead of sinning straight up, the top (or Earth in this case) slowly sways in a circle, causing the direction Earth points in space to change over time.
Precession is the movement of Earth’s axis in a cone shape that results from this wobble.
Precession is caused by the gravitational forces of the Sun and the Moon pulling more strongly on Earth’s equatorial buldge.
Define angle of obliquity/axial tilt/tilt of rotational axis (how is it measured?)
The angle of obliquity is the angle between a planet’s rotational axis and a line perpendicular to the planet’s plane of orbit.
(the tilt of the planet’s axis is measured relative to the perpendicular of it’s plane of orbit)
Define rotational axis (also called just ‘axis’)
The imaginary line through a planet around which the planet rotates/spins
Define plane of orbit/ orbital plane/ ecliptic
What is ‘inclination’ of a planet’s orbital plane (how is it measured?)
Orbital plane or ‘ecliptic’ is the path that a planet follows as it orbits around the sun.
The inclination of a planet’s orbital plane is measured relative to a reference plane – for our Solar System, this is the equatorial plane of the Sun
A planet’s ecliptic is said to have zero inclination if it aligns exactly with the equatorial plane of the sun.
The angle between the planet’s orbital plane and the sun’s equatorial plane is the inclination.
What phenomenon results from precession?
precession, the slow change in movement of earth’s axis, results in Earth’s poles changing position over time.
This means the north pole star changes.
What was the north pole star when the Egyptian pyramids were built?
What is the north star now?
What will be the north star in 12,000 years?
(and which constellation are they in)
The north pole star at the time the Egyptian pyramids were built was Thuban in the constellation of Draco.
The current north pole star is Polaris, in the constellation of Ursa Minor
The north pole star in 12,000 years will be Vega in Lyra
What interesting discovery was made about the Egyptian pyramids in the 1800’s
It was discovered in the 1800s that the Great Pyramid (Cheops) was astronomically aligned with Thuban at the time it was built (Thuban was the north pole star at the time)
What is the generator of Earth’s magnetic field?
generated by electrical currents in the iron-rich core.
Interaction of the liquid metal of the outer core flowing past solid metal of the inner core establishes an electrical current which in turn produces a magnetic field.
What is the strength of Earth’s magnetic field compared to the other terrestrial planets?
Of the terrestrial planets, Earth’s magnetic field is uniquely strong; Mercury has a much weaker magnetic field, Venus has none, and Mars’ field is extremely weak.
What is the composition of Earth’s atmosphere?
- 78% nitrogen
- 21% oxygen
the other 1% contains traces of many elements and compounds, including
* argon
* carbon dioxide
* water
* krypton
* xenon.
Describe the early period of Earth’s life (what happened during the first 20 million years?)
Describe the conditions of Earth at this time
It was a violent and chaotic time, as **Earth was growing by accretion. **
The first large object would have attracted others by simple gravity; as the object grew larger, it attracted more and more material to it faster and faster.
This means there was tonnes of impacts with smaller bodies, each one releasing kinetic energy, so Earth was very hot.
It’s generally agreed that at least the top 500 km of Earth was melted during this period.
What 5 elements make up 95% of Earth’s composition. What percentage does the most abundant element account for?
The 5 elements that make up 95% of Earth’s composition
* iron (Fe)
* oxygen (O)
* magnesium(Mg)
* silicon (Si)
* sulphur (S)
with iron alone accounting for roughly 30%.
describe the zonation of Earth during the early period when all Earth was molten (molten means liquified by heat)
during the period when all Earth was molten, there was a general zonation of elements from heaviest at the core to lightest at the top; of course, the zonation was not complete, so there still are many heavy elements at surface.
What large scale geological processes take place in the lithosphere and asthenosphere?
Earthquake activity
Volcanic activity
Creation of ocean basins
Mountain building
- Draw a diagram of Earth’s layers (differentiated zones) with accurate proportions for both the old scheme and new scheme. What are the exact distances underneath the surface of each layer?
- Describe/define each layer for the new scheme
Lithosphere (up to 100km beneath surface)
* encompassing the crust and upper portion of mantle
* solid, relatively strong, rocky layer
Asthenosphere (100km-350km below surface)
* heat softened layer of rock
* relatively weak
* slow flowing (almost plastic)
Mesosphere (350km-2890km)
* the confining pressure is so great that the rock has to be solid, but the temperature (while not as high as in the core) is high enough that the material acts like a very stiff plastic (i.e., it will yield, but slowly).
Outer Core (2890km-5150km)
* liquid layer of the core
* mostly composed of iron
* almost 100% metal
Inner Core (5150km - 6371km)
* solid layer of the core
* mostly composed of iron
* almost 100% metal
* estimated between 5000 and 7000 degrees celcius
When was Earth’s differentiation complete?
probably complete by 4.4 billion years ago.
Define differentiation
The process of chemical zonation from core to surface is called differentiation
What are the different zones of Earth as per the old scheme?
What is the zonation of Earth as per the slightly newer scheme?
What are the divided categories in the old scheme vs. new scheme based on?
Old scheme (based on chemistry):
* Crust
* Mantle
* Core
Slightly newer scheme (based mainly on physical properties):
* Lithoshpere
* Asthenosphere
* Mesosphere
* Outer core
* Inner core
Describe Earth’s core:
What are the 2 different parts, which is solid and which is liquid? What is the composition of Earth’s core?
Earth’s core is divded into 2 parts:
The liquid outer core
The solid outer core
Both are almost 100% metal, mostly composed of iron.
What is the temperature in Earth’s inner core?
The temperature of the inner core is thought to be somewhere between 5000 and 7000°C – which makes it hotter than the Sun’s surface (which is about 5500°C).
What are the 2 dipoles of Earth’s magnetic field?
The north magnetic pole
The south magnetic pole
What are magnetic field lines?
Invisible lines used to visually represent a magnetic field. They describe the direction of the magnetic force.
What is a dynamo
The most practical mechanism by which to generate a magnetic field is a dynamo.
This is simply a mechanical device that converts physical energy to electrical energy
Anywhere that electrical energy flows, there’s a magnetic field surrounding it.
What results from electrical energy flowing?
electrical energy flowing always results in a magnetic field surrounding it.
Why is Earth’s rotation gradually slowing
Earth’s rotation is gradually slowing because of the glancing impact that produced the moon
Explain how Earth’s gradually slowing rotation is related to Earth’s magnetic field
Because of Earth’s gradually slowing rotation, it’s outer core spins faster than it’s outer core
This is becasue the inner core is slower to respond to any outside forces, because it is surrounded by liquid.
The spinning of one metal inside another is the basis of construction of a dynamo because it is what generates an electrical current, which in turn generates a magnetic field.
Why do the poles of Earth magnetic field change?
occasional turbulence in the hot liquid of the outer core periodically disrupts the process to the point that the dynamo gets thoroughly confused
Describe the ‘iron catastrophe’.
What period in Earth’s history did this happen?
What was the result of this event?
- The iron catastrophe happened during the early period of Earth, when it was growing by accretion
- the impacts during accretion made Earth hot and caused the outer 500km of Earth to melt
- as it melted, the heaviest stuff, mainly iron, sunk towards the center of Earth, becausae it was heavier.
- This sinking movement released even more energy and caused the whole planet to melt
- This was so quick and chaotic that it was named the iron catastrophe.
- As Earth grew and got squeezed tighter by its own gravity, the very center of the core turned solid.
The main effect of the iron catastrophe was on the distribution of elements - the iron catastrophe resulted in Earth having almost a 100% metal core composed of mostly iron (and some other heavvy metals)
This is because it removed most of the heavy metals from the surface, since they all sunk to the core. Obviously, since heavy metals preferentially ended up at the center, the lighter stuff ended up at the top
(lots of silicon, aluminum, oxygen)
What important event happened after the main period of accretion in Earth’s history?
The impact with the Mars-sized planet named Theia which totally reshaped Earth and resulted in the formation of the moon.
What causes fluctuations in Earth’s magnetic poles? What kind of fluctuations/activity happens with the magnetic poles?
Occasional turbulence in the liquid outer layer of Earth’s core cause the dynamo to get confused, leading to fluctuations of the magnetic poles, and gradual pole reversals.
Magnetic Pole Reversals:These are the long-term changes where the north and south magnetic poles completely swap places. this process takes thousands to tens of thousands of years to complete. During this time, the Earth’s magnetic field weakens, and the poles can move unpredictably, which might be what the notes hint at with the compass needle swinging wildly.
Short-Term Magnetic Fluctuations:Besides the slow pole reversals, the Earth’s magnetic field can also experience more rapid and short-term fluctuations. These can cause the compass needle to swing or shift direction over shorter periods—days to years—but these are not full pole reversals.
What is the important point to take away from the unstable nature of Earth’s magnetic poles?
The important point to make is that throughout history, Earth’s magnetic poles have sometimes been exactly as they are now (which we call ‘normal’) and at other times completely the opposite, with our north magnetic pole then becoming south magnetic pole (which we call ‘reverse’).
What direction will a free flowing magnet orient itself no matter where you are on Earth?
free flowing magnets in Earth’s magnetic field will always orient themselves to point towards the north magnetic pole, no matter where they are.
What has been the gradual direction of Earth’s magnetic north pole? What does the gradual movement of the poles tell us about Earth’s dynamo
The magnetic north pole is has been slowly migrating over the Arctic regions and has moved from Canadian territory into international territory – and is headed for Russia.
The gradual movement of Earth’s poles proves that Earth’s dynamo is every changing (the processes in the core that generate the magnetic field are every changing)
What are plates?
What is plate tectonics?
What are plate boundaries/margins?
The Earth’s surface is divided into big pieces called “plates.” These plates are segments of the lithosphere.
plates can move because of forces deep inside the Earth. This movement is called “plate tectonics.”
Plate boundaries/margins are where the plates meet. Since they are regions of interaction, they are where most of the world’s earthquakes and volcanic eruptions happen.
How do the other terrestrial planets compare to Earth in terms of tectonic activity?
Other terrestrial planets likely have similar structures and compositions to Earth, but apparently not the same tectonics: we cannot detect distinct plates or evidence of those tectonic processes that move lithosphere/crust segments.
Why is the concept of plate tectonics important to understand?
Plate tectonics explains many aspects of Earth:
* the distribution of minerals and rocks, which we use for resources
* the composition of our atmosphere and hydrosphere.
Understanding it helps explain why Earth’s landscape is the way it is and how it has changed over time.
Describe what is depicted in this image
The image shows Earth’s plates and the direction in which they are moving. We are on the North American plate.
What was the earliest evidence of vertical movements of rock?
(Who discovered, when, what did they determine?)
**Leonardo Da Vinci (1508) **
* discovered seashell fossils high in the mountains in Italy
* he determined that this could only be for 2 reasons: Earth was once covered in water (even up to the mountains) or the ocean floor had uplifted.
* since seashell fossils are not found uniformly across Earth’s surface, it must have been that the ocean floor had rised
What was the second piece of evidence of vertical movement of rocks?
(Who discovered, when, what did they observe)
When did the concept of vertical movement finally become accepted?
Charles Darwin (1830s)
* during his trip in Beagle, he noticed that part of Chile’s coastline had been raised up as a result of a huge earthquake.
The idea gradually took hold and was finally accepted by the middle of the nineteenth century.
Who first proposed the idea of continental drift (the idea that earth could move horizontally) and what did he propose?
What evidence led him to this idea?
Why was this idea not accepted and originally abandoned?
Alfred Wegener (1914)
* proposed the concept of continental drift (first proposition that Earth could move horizontally)
* he proposed that the continents (north america, south america, europe, africa) were once all connected as a supercontinent named pangea
* he proposed that somehow panea broke and spread apart into the continents we know today
What evidence did he have?
* he was fascinated by the coaslines of the continents looking like a jigsaw puzzle
* closer study showed that certain features in continents, such as mountain chains or bands of fossils, could be connected across the gap of the ocean
Why it was not accepted at the time
* Alfred did not have an explanation for the continental drift, there was no mechanism discovered that would cause this.
* Because of this, the idea was abandoned until 1940s when they discovered the mechanism for continental drift.
What is Pangea
Pangea was the supercontinent that the current continents broke off from becasue of continental drift.
What technology was developped during the Second World War that (accidentally) led to the revival of the idea of continental drift?
During the Second World War some technology was developped that helped provide a process for the drift mechanism.
The allies developped magnometers (sensitive instruments that detect magnetic patterns). These were hauled behind ships to detect sunken German submarines.
The magnometers detected a magnetic pattern of Earth’s crust which revived Alfred Wegener’s hypothesis of continental drift and ultimately led to its acceptance.
What is the name for the study of magnetic properties of rocks?
paleomagnetism (paleo means ancient)
What is magnetite?
Where is it most commonly found?
- an iron oxide
- one of the relatively few natural minerals that can become permanently magnetized (responsive to a magnetic field)
- very common
- most commonly found in basalt (a volcanic rock)
What is basalt? How does it form and what forms within it?
Basalt forms from lava and is the most common rock on Earth. When lava cools to form basalt, magnetite forms within the basalt rock. Magnetite is the natural mineral within basalt that has magnetic properties and can become permanently magnetized.
What pattern was found in the magnetic properties of the ocean floor along the Mid-Atlantic ridge which led to the acceptance of plate tectonics?
The Mid-Altanic Ridge is like a mountain range under the sea.
Samples from this area showed a pattern of magnetic stripes/bands on both sides of the ridge that are symmetrical (the ages and polarity of the stripes were a mirror image on both sides)
This proved that the seafloor was spreading - as it spread, lava leaks out from the inside of earth onto the seafloor. As it cools into basalt, magnetite forms inside and orients to the direction of the magnetic pole at the time it was created, then solifies in that orientation. Then it is pulled apart as the seafloor spreads again, repeating the process and creating this stripe pattern with alternating polarities.
What concept is illustrated in this image
seafloor spreading - the first hard evidence of horizontal movements of earth, which led to the acceptance of plate tectonics.
the seafloor spreaks and lava from inside earth leaks up to the surface, then cools into basalt with magnetite forming inside the basalt and orientating to the direction of the magnetic north pole at the time, then solidifying in place, forming a pattern of magetic stripes with alternating polarity.
What are the 3 types of plate boundaries/margins that result from the 3 types of movement of tectonic plates?
Divergent boundaries (spreading centres):
* Where plates move apart, creating new crust
* Example: the Mid-Atlantic Ridge
Convergent boundaries (subduction zones):
* Where plates move towards each other, and one plate may slide beneath another (subduction)
* usually the denser plate is the one that ends up underneath
* this ‘recycles’ the crust back into the mantle (material at the surface goes back into the earth)
* Example: the convergent zone marking the western edge of the whole South American continent.
Transform boundaries (strike-slip faults):
* Where plates slide past each other horizontally
* causing friction but not creating or destroying crust.
* Example: San Andreas Fault in California
What is represented in this image?
This image shows the cross sections through the mesosphere from data gathered through seismic tomography
Seismic Tomography:This is a method used to visualize the inside of the Earth by measuring how seismic waves travel through it. Different materials and temperatures affect the speed of these waves.
The little boxes are cross sections of the mesosphere – in this context cross sections are like vertical slices through the Earth’s interior at specific locations. Imagine cutting a vertical slice through a cake to see the layers inside—these cross sections work similarly but for the Earth’s mesosphere.
The blue arrows drawn on earth’s surface represent where this slice of the mesosphere is under the surface.
Blue Blobs in the Image: The blue areas in the cross-sections represent **cooler sections of the mesosphere, where segments of lithosphere have sunk down **and are breaking up as they move toward the core.
Therefore, this provides evidence that pieces of the lithosphere have dropped through the asthenosphere and into the mesosphere.
Blue arrows: the blue arrows indicate where the cross sections intersect with Earth’s surface – notably they all pass through plate boundaries!!
What concept is represented by this image?
this image shows mantle plumes
Mantle plumes are like very hot balloons of rock material that rise up through the different layers of the Earth. They start deep in the Earth near the boundary between the outer core and the mesosphere (lower mantle), where it’s extremely hot.
Because they are hotter and less dense than the surrounding rock, these plumes rise through the mantle
What is represented in this image?
This image represents relative age dating of rocks in the Grand Canyon
- The oldest rock is at the bottom, 1a
- Then 1b, which is a granite that intrudes and cuts across the layers of 1a
- Then sequence 2 - those layers are tilted and cut off at the top, so erosion must have occured
- Then later in time layers 3-6 were deposited on top
draw a diagram and label the parts of a prokaryote
Explain the life-death cycle of prokaryotes and how we got this information from rocks. how long did this life-death cycle last? and how did it finally come to an end?
prokaryotes produce oxygen, and the iron in the ocean absorbed the oxygen, forming a layer of red iron oxide on the ocean floor.
The oxygen eventually killed the organisms (because oxygen is poisonous to anaerobic organisms), thus creating a layer of white coloured sediment lacking in iron oxide
As soon as the organisms flourish again, the cycle repeats.
This created ‘banded iron’, the rock with layers of red iron oxide and white sediment rock
- we are not sure how long this lasted, seems to be around 2 billion years
- During that time, most of the available iron in solution in seawater was finally consumed, and free oxygen began to appear.
