Chapter 7: Earth Flashcards

Question

Define differentiation

Answer 1

The process of **chemical zonation from core to surface** is called differentiation

Answer 2

**Old scheme (based on chemistry):** * Crust * Mantle * Core **Slightly newer scheme (based mainly on physical properties):** * Lithoshpere * Asthenosphere * Mesosphere * Outer core * Inner core

Answer 3

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.

Answer 4

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).

Answer 5

The north magnetic pole The south magnetic pole

Answer 6

Invisible lines used to visually represent a magnetic field. They describe the direction of the magnetic force.

Answer 7

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.

Answer 8

electrical energy flowing always results in a magnetic field surrounding it.

Answer 9

Earth's rotation is gradually slowing because of the glancing impact that produced the moon

Answer 10

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.

Answer 11

occasional turbulence in the hot liquid of the outer core periodically disrupts the process to the point that the dynamo gets thoroughly confused

Answer 12

* 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)

Answer 13

The impact with the Mars-sized planet named Theia which totally reshaped Earth and resulted in the formation of the moon.

Answer 14

**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.

Answer 15

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’**).

Answer 16

free flowing magnets in Earth's magnetic field will always orient themselves to **point towards the north magnetic pole**, no matter where they are.

Answer 17

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)

Answer 18

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.

Answer 19

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.**

Answer 20

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.

Answer 21

The image shows Earth's plates and the direction in which they are moving. We are on the North American plate.

Answer 22

**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

Answer 23

**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.

Answer 24

**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.

Answer 25

Pangea was the supercontinent that the current continents broke off from becasue of continental drift.

Answer 26

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.

Answer 27

paleomagnetism (paleo means ancient)

Answer 28

* 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)

Answer 29

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.

Answer 30

magnetized rock is responsive to a magnetic field.

Answer 31

**The Curie point (580°C) is the temperature below which magnetite particles can align with the Earth's magnetic field and become permanently magnetized.** It marks the threshold at which magnetite in cooling basalt can start recording the magnetic field.

Answer 32

When basalt cools below the Curie point, the magnetite grains within align according to the Earth's magnetic field at that time. Once the basalt solidifies, these grains are locked in place, preserving a record of the magnetic field. This is preserved as long as the rock is unaffected by external factors like erosion.

Answer 33

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.

Answer 34

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.

Answer 35

age dating the basalt rocks containing the magnetic polarity reversals tells us how fast the seafloor is spreading This movement is remarkably fast in some places today, as high as 17.2 cm/yr, but most places it is only 2 - 4 cm/yr

Answer 36

Seafloor spreading results in new crust being created, which would increase the surface area of Earth. Since Earth is not getting larger over time, it would not make sense for spreading to be the only process of plate tectonics, there must be other processes to balance this out. The processes of crust creation and destruction don’t necessarily need to occur simultaneously or at the exact same rate. However, over geological time scales, they do balance each other. This means the total surface area of the Earth remains approximately constant, despite local or temporary variations where one process might dominate. The processes of crust creation (from spreading - diverging movement) and destruction (from subduction - converging movement) don’t necessarily need to occur simultaneously or at the exact same rate. However, over geological time scales, they do balance each other. This means the total surface area of the Earth remains approximately constant, despite local or temporary variations where one process might dominate.

Answer 37

**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

Answer 38

They both occur along plate margins (regions of interaction) Earthquakes occur along all three types of plate margins. Volcanic eruptions only occur at divergent and convergent types.

Answer 39

direct measurements made using GPS.

Answer 40

Convection: the movement caused within a fluid by the tendency of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat. Convection is the process that makes the plate move (while magnetic patterns provide evidence that the plates move, convection is the reason WHY the plates move) So how is convection involved with plate tectonics? Heat is produced in the Earth due to radioactive decay This heat provides the driving force to move material around in the process of convection The mesosphere, even though it is made of solid rock, behaves a bit differently over very long periods of time. Despite being solid, the intense heat and pressure inside the Earth allow these rocks to flow very slowly, much like a thick, slow-moving liquid. Therefore, even though the mesosphere is solid, it's fluidity over time allows it to maintain convection currents. Thus, hot material from the base of the mesosphere can rise toward the surface, to be replaced by colder material from the top. The plates at the surface simply ride on top of these large scale convection currents.

Answer 41

The movement of tectonic plates is caused by convection currents in the mantle, driven by heat from radioactive decay inside the Earth.

Answer 42

Subduction is when one tectonic plate moves under another and sinks into the mantle due to converging movements, often leading to volcanic activity and earthquakes.

Answer 43

Convection is a process that occurs in liquids where hotter material rises and the cooler material sinks (material is more dense when it is cooler so the cooler material sinks). Convection is the process that causes the plates to move, thereby providing the WHY of plate tectonics. **How does this process work?** * **Heat** is generated within the Earth from **radioactive decay** * This heat allows **convection currents to be maintained in the mesosphere**-- the mesosphere is solid, but if you look at it over long periods of time, it flows very slowly, acting like a slow-moving liquid because of the heat * Therefore, hot material in the mesosphere rises to the surface, and cool material sinks. * **The plates at the surface simply ride on top of these large scale convection currents.**

Answer 44

radioactive decay within the earth is what produces the heat which allows convection currents to be maintained in the mesosphere, and this movement of material in the mesosphere is what causes the plates that are riding on top of it to move

Answer 45

When two plates converge in the process of suubduction (one gets pushed beneath the other), the plate which is pushed underneath can get carried further down by the convection currents, pulling the plate down through the asthenosphere and into the mesosphere.

Answer 46

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!!

Answer 47

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**

Answer 48

**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**

Answer 49

Mantle plumes are less dense because their material is much hotter than the surrounding rock, which makes them buoyant and causes them to rise through the mantle.

Answer 50

Upon reaching the lithosphere, the intense heat and pressure of the plume can immediately affect the brittle, cooler material of the lithosphere. There are generally two scenarios that can occur: **A. Immediate Breakthrough:** In some cases, the plume breaks through the lithosphere almost right away. This can lead to the formation of one or two volcanoes where magma (molten rock) from the plume reaches the Earth's surface. This magma flow can be almost continuous, leading to highly active volcanic areas, like those seen in Hawaii. **B. Gradual Accumulation:** Alternatively, the hot material from the plume might not break through the lithosphere immediately. Instead, it can accumulate just beneath the lithosphere, heating and weakening it over time. This accumulated magma causes the lithosphere above it to bulge upwards until one or more breaks occur and a string of volcanoes result

Answer 51

volcanoes are formed when magma (molten rock) breaks through the lithosphere. This happens when mantle plumes (which are melted rock, 'magma') rise from the core up to the base of the lithosphere. If the magma breaks through the lithosphere right away, it can result in one or two volcanoes forming with a continuous flow of magma (like in Hawaii) If the magma does not break through right away and accumulates under the surface, it causes the lithosphere to bulge, and when it eventually breaks through it can form a string of volcanoes

Answer 52

relative age dating * you get an age relative to the rocks around it * allows geologists to determine the order in which rock layers were formed without knowing their exact age in years. By examining the arrangement of these layers, scientists can infer which rocks are older and which are younger based on their position relative to each other. absolute age dating * you can get an absolute years old

Answer 53

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

Answer 54

Typically, in an undisturbed sequence of sedimentary rocks, the **oldest layers are at the bottom and the youngest are at the top.**

Answer 55

* 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

Answer 56

Sedimentary rocks are rocks formed by the accumulation and consolidation of sediments. Sediments are particles of mineral or organic matter that are being carried by a medium (water or air). As the conditions of the medium change (like river slowing down when reaching a lake, or wind speed decreasing) the particles start to settle. The settling of these particles which form rocks is what we are talking about with rocks being 'deposited' Therefore, sedimentary rocks are an indication that there was once water there, but not guaranteed because they can also be formed in air

Answer 57

Rock Sequence: This refers to the order and position of layers of rocks as they appear in the ground. A rock sequence can show a "stack" of different types of rock layers, each representing a period of deposition that occurred over time. By studying the sequence, geologists can understand the geological history of an area.

Answer 58

**Establishing a geological time scale** * If a rock sequence containing a specific type of fossils (ie. a very particular shell or assembly of shells) is found in different locations and the sequence and type of fossils match, then you know these rock sequences are the same age. * If one rock sequence is beneath another in an undisturbed geological context, it is considered older. This principle helps establish a relative age scale where scientists can organize Earth's history based on rock formations and fossil content. By comparing rock sequences and fossil assemblies from various parts of the world, Earth scientists can match layers and establish a worldwide geological timeline. This timeline categorizes rock formations into different periods based on their age relative to each other.

Answer 59

If a rock sequence containing a specific type of fossils is found in different locations and the sequence and type of fossils match, it suggests that these rock layers were formed during the same geological period. This allows geologists to correlate or link the age of rocks from different locations.

Answer 60

a geological time scale is a representation of time based on the rock record of Earth; a system of chronological dating

Answer 61

**Proterozoic era:** * the big block of time BEFORE 545 million years ago * Proterozoic means development of life * most life was soft-bodied and consisted of simple cells, with no significant hard parts to be preserved as fossils. **Phanerozoic eon:** * all of time from the Cambrian Period until present day (Cambrian period is the first phase of paleozoic time period which is the first phase of phanerozoic) * abundant, complex life **Paleozoic** (early life) **Mesozoic** (middle life) **Cenozoic** (recent life) (the 3 eras within phanerozoic also have subdivisions of time periods)

Answer 62

**End of the Paleozoic era - Start of Mesozoic era** * **At 251 million years ago,** * there was a major extinction event (may have been an asteroid impact but no hard evidence what it was) * about 96% of species disappeared from Earth. * ended the Permian period (end of the paleozoic era) and started the Triassic period (start of the mesozoic era) **End of Mesozoic era - start of Cenozoic era:** * **At 65.5 million years ago,** * an asteroid impact that killed 70-75% of all species, including most dinosaurs * marked the end of the Cretaceous period (last Mesozoic period)

Answer 63

Following **the discovery of radioactivity in 1896**, scientists have been able to determine numerical ages of rock units (which, of course, made it possible to assign those numerical values you see on the geological time scale). Radioactivity provides a ‘clock’ that begins running when radioactive elements are sealed into minerals. To say that an element is radioactive is to say it is unstable or that it ‘decays’

Answer 64

The rates at which radioactive elements decay have been measured and duplicated in many laboratories. Information we need to determine age of rocks: * The rate of radioactive decay (we call that rate the **half-life**) * The **amount of the parent isotope** (the isotope that is in the process of breaking down * The **amount of the daughter isotope** (the isotope produced by the breakdown

Answer 65

we are dating the exact time at which rock cooled from lava

Answer 66

**Uranium and Thorium** **Why?** These are the most commonly used because it takes millions to billions of years for the parent to decay, making them good to use for even the oldest rocks **Uranium parent isotopes:** * 238-U * 235-U **Thorium parent isotope:** * 232-Th **Both of these elements end up with a daughter isotope of lead:** * 206-Pb * 207-Pb * 208-Pb

Answer 67

* you could use an isotope of carbon that’s radioactive. * the carbon method will work only for something up to 100,000 years old

Answer 68

**Earth is 4.5 billion years old, but it's surface is younger** **Why?** This is because Earth is so geologically active, so it's surface is constantly changing * The oldest surviving rocks we can find on Earth's surface are about **4 billion years old**. * Ocean floors are even younger because they are constantly being renewed by plate tectonics; it's rare to find any part of the ocean floor that is older than **250 million years.**

Answer 69

the ages of rocks and the magnetic records give us information about the movement of tectonic plates, even dating back to the break up of Pangea, which started 200 million years ago?

Answer 70

* the composition of our atmosphere * liquid water on surface (forming a part of our hydrosphere) * our biosphere (life)

Answer 71

Photosynthesis is the process where plants use **sunlight, water, and carbon dioxide** to produce **oxygen and sugar**. It's important because it produces the oxygen in our atmosphere and supports life.

Answer 72

The oceans provide a huge **heat reservoir** that stabilizes Earth's climate, keeping it at optimal levels for life.

Answer 73

Earth's unique composition of atmosphere, atmospheric pressure, and density are all intimately related to: * the abundance of liquid water on surface (acts as heat resevoir, stabalizes surface temperature) * the abundance of plant life that uses photosynthesis (produces oxygen for atmosphere)

Answer 74

Hydrogen and helium - no good for supporting life original atmosphere called primordial atmosphere

Answer 75

Earth’s closest planetary neighbours, Venus on the Sun-side and Mars on the other, have atmospheres composed of approximately: * **96% carbon dioxide (CO2)** * **2-3% nitrogen (N2)** * **lesser amounts of various other elements.** Earth's atmosphere changed from the original/primordial atmosphere (helium and hydrogen) to an atmosphere like the current ones of our planetary neighbors **4.5 billion years ago, around the time when Earth's surface solidified**

Answer 76

the amount of atmosphere (thicker atmosphere = more atmospheric pressure)

Answer 77

The atmospheric pressure (amount of atmosphere) was very different: * Earth = 1 bar * Mars = 0.07 bars (very thin) * Venus = 90 bars (crushing pressure, very very thick)

Answer 78

* Earth's atmospheric pressure = 1 bar * Mars' atmospheric pressure = 0.07 bars * Venus' astmospheric pressure = 90 bars This means Mars' atmosphere is very thin, equivalent to what Earth's would be at 35 km altitude. In contrast, Venus' atmosphere is crushing, comparable to the pressure on Earth found 1 km deep in the ocean

Answer 79

**Mars has only 10% the mass of Earth**, and we can explain the thinness of its atmosphere through the hypothesis that **Mars' weak gravity** was **unable to hold its atmosphere**, thus much of that atmosphere was lost early in the planet's life.

Answer 80

Venus is similar in size and mass to Earth, so the difference in atmospheric pressure is NOT due to gravitational forces. **The difference is due to the presence of liquid water:** * liquid water on earth dissolves carbon dioxide, lessening the amount of the gas in the air and thus reducing atmospheric pressure. * Therefore, Venus' atmosphere is much thicker becuase of the absence of liquid water to dissolve CO2 * CO2 produces a greenhouse effect, so Earth having less of it meant it had lower temperatures than Venus, which allowed it to support life

Answer 81

* Water dissolves carbon dioxide, which lessens the amount of this gas in the air (reducing atmospheric pressure) * carbon dioxide produces a greenhouse effect, keeping heat inside, so dissolving the CO2 lowered Earth's temperature to a point that made it possible for life to evolve

Answer 82

Volcanic gases formed the atmospheres of the terrestrial planets * evidence shows that volcanism started early in terrestrial planet's history * volcanoes released large amounts of carbon dioxide (CO2) and water (H20) * the early volcano-derived atmosphere did NOT have oxygen (O2)

Answer 83

* 4.0 - 4.5 billion years ago, Earth was constantly getting pummeled by comets and asteroids * Each comet and asteroid had small amounts of water * the water stayed as vapour in the atmosphere when Earth was very hot * as earth cooled, the water vapour turned to liquid and rained down * this resulted in the liquid water on earth's surface (lakes, oceans and rivers)

Answer 84

The hydrosphere is the combined mass of water found on, under, and above the surface of a planet.

Answer 85

Apart from the occasional impact of water-rich comets, Earth's hydrosphere is largely a closed system. This means that the Earth neither loses nor gains water; it is clear that we have been recycling the water for a long time.

Answer 86

The early Earth was hot and steamy with a primordial ocean close to boiling, and the CO2 levels in the atmosphere were much higher than today, many times today's level.

Answer 87

* Microscopic fossils provide evidence that life existed in the sea at least 3.5 billion years ago * there is additional, though somewhat ambiguous, chemical evidence that life was present as much as 3.8 billion years ago.

Answer 88

The first microscopic life most likely appeared in the ocean because it was sheltered from the harsh atmosphere.

Answer 89

the development of the biosphere (life) slowly started to change the atmosphere in ways that made it friendlier for the biosphere to grow even larger.

Answer 90

**by several hundred million years ago**, it was possible for life to leave the sea, stay continuously in contact with the atmosphere, and spread to the land.

Answer 91

* Photosynthesis allows plants to take in CO2 and water and produce oxygen and organic matter, adding oxygen to the atmosphere. * The biosphere reduces CO2 levels by forming organic matter and limestone, which store carbon that was originally in the atmosphere (caused temperature to decline)

Answer 92

the biosphere reduces CO2 levels by forming organic matter and limestone, which store carbon that was originally in the atmosphere removal of CO2 from atmosphere means less greenhouse effect and lower temperature

Answer 93

The Earth system, including the biosphere and atmosphere, is still evolving, with the atmosphere being the most sensitive to it's changes: * volcanoes still give off gases (CO2 and H20) * biosphere still produces oxygen

Answer 94

the atmosphere

Answer 95

there are no other known planets that have the right conditions for liquid water to exist on the surface (though Titan may have liquid ethane and methane, and Europa may have liquid water beneath the surface)

Answer 96

Liquid water is also responsible for most of the erosion and weathering of Earth's continents, a process unique in the solar system today (though it appears to have occurred on Mars in the past).

Answer 97

environment with no free oxygen

Answer 98

If life were to develop in an environment containing no free oxygen (an anaerobic environment), it would probably get energy from a process like **fermentation (breakdown of carbohydrates).**

Answer 99

* the first life * single cell organisms * fossils found up to 3.5 billion years old

Answer 100

First life (single cell prokaryotes) were formed in an anaerobic environment (the ocean) They were capable of photosynthesis (producing oxygen). But, oxygen is poisonous to anaerobic organisms. This creates a paradox: how could the oxygen-intolerant organisms survived the oxygen that they themselves produced?

Answer 101

This apparent contradiction was possible because of the peculiar conditions that existed in the water of the ancient oceans. Unlike today’s oceans, they were **enriched in dissolved iron** if you leave metal iron sitting in the open air, it will rapidly rust (i.e., it will oxidize) by absorbing free oxygen from the air. **Iron has a strong ability to absorb oxygen.** As the primitive oceans contained no free oxygen, iron atoms would have existed happily. However, t**he oxygen produced by photosynthesis by these most primitive organisms would have quickly combined with iron**; oxidized iron is quite insoluble in water, so **a red coloured iron oxide would be precipitated to the ocean floor.**

Answer 102

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.

Answer 103

because without oxygen in atmosphere, there would be no ozone, and ozone is the thing that protects us from the ultraviolet radiation of the sun (remember that ozone reacts strongly with cosmic radiation, thus shielding us from damaging effects)

Answer 104

when most of the available iron in the ocean was consumed by oxygen and had transformed into red iron oxide rock which sunk to the ocean floor, this finally allowed an envrionment with free oxygen. Eukaroytic cells appeared as soon as there was free oxygen

Answer 105

* they used oxygen for respiration * they grew rapidly in large colonies * they were truly photosynthetic (producing large amounts of oxygen) * Thus contributed a great amount of oxygen to the atmosphere, and rapidly changed the biosphere of Earth.

Answer 106

* As land forms rose above sea level - primarily as a result of volcanic deposits - weathering (by acidic rain) and erosion proceeded. * A multitude of elements ended up in solution in seawater as a result. * Then, as today, calcium (Ca) was a major component carried by the slightly acidic ‘fresh’ water of rivers to the sea (because it’s a major component of the rocks that weather!). * Once in the seas, Ca may chemically combine with carbon dioxide and form grains of calcite (CaCO3) which precipitate and form limestone, or may be consumed, again with carbon dioxide, to form skeletons/shells for marine organisms. * In either case, CO2 is removed from the ocean water/atmosphere * if all the CO2 currently tied up in either inorganic or organic deposits of CaCO3 were released, Earth’s atmosphere would again consist dominantly of carbon dioxide.

Answer 107

They help move CO2 from the atmosphere to organic and inorganic 'sinks' (like plants and the ocean floor) and back again, balancing the amount of CO2.

Answer 108

Even though there's only a little CO2 in the air, it's super important because it helps keep the Earth warm through the **greenhouse effect.** This effect **warms our planet by about 35°C**, making it nice and comfortable instead of freezing cold. Without the greenhouse effect, Earth's average surface temperature would be around -21°C instead of +14°C, likely causing the oceans to freeze and making life as we know it impossible.

Answer 109

the presence of free oxygen is remarkable because free oxygen is chemically reactive and would normally combine with other elements. * It is maintained by biological processes, primarily photosynthesis, which keeps it available for life. * Without life there would be no free oxygen, and Earth would be a very different planet!

Chapter 7: Earth Flashcards

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