Geology - All Los - G11 final revision- S2.pptx

Geology - All Los - G11 final revision

1. LO 9 : Geologic History of the Geosphere

2. What is Geologic Provinces ? A large region of Earth’s surface with common geologic history like the common ( Folds , Faults , Earthquakes , Volcanos and orogens ) happened in a certain area in certain time Here is an example for one of the geologic provinces made for the world :

3. Earth’s History The oldest oceanic crust is not older than 200 million years where the continental crust of rocks is much younger than that . The Earth was formed about 4.6 billion years ago , back then Earth was probably fairly small , it was third its size now . The growth of this planet is due to the attraction of the debris of the solar system . Examples of the debris of solar system is ( asteroids , meteors and comets ) . Earth was a hostile place back to 500 million years where it wasn’t a place that is sustainable for life this is due to the presence of much volcanos and the spontaneous hit of meteorites in Earth’s surface .

4. The spontaneous hit of many meteorites provided Earth internal heat which made the young Earth’s surface molten . The heat in this young Earth was 3 times of the internal heat of Earth now . The very young Earth is called Hadean . Named for Hades the god of the underworld in the Greek mythology . After while , the hit of meteorites and eruption of volcanos were slowed down . That resulted in the cooling down of OUTSIDE of Earth . In that time , A few minerals begun to crystalize and something like scum patches begun to form in the molten surface and they were able to move around a lot which resulted in the destruction of the unstable surface of the Hadean by melting .

5. Also this melting was an impact of meteorites . Some of the melted material was recycled into the mantle . Because of the high temperatures in the upper mantle , most of the oceanic and continental crust was in the form of BASALT which had the ability to stay stable in high temperatures like those who crystalize in the mid-ocean ridges ( explained in the upcoming slide ) . Due to the melting and remelting of basalt rock , GRANITE was formed as recycled rocks .

6. The oldest material on Earth Zircon is the oldest continental material in Earth’s surface , its chemical name is zirconium silicate . It is hard and durable . It was originally formed as igneous rock which means that it was formed due to cooling of magma but due to the weathering process it was recycled to younger sedimentary rocks . Its age is nearly 4.4 billion years old . Its image :

7. Mid-ocean Ridges It is something related to plate tectonics but here is a quick hint for what is it helpful for and why does it happen : The mid-ocean ridge is a continuous range of undersea volcanic mountains that encircles the globe almost entirely underwater they occur along the kind of plate boundary where new ocean floor is created as the plates spread apart. Thus the mid-ocean ridge is also known as a "spreading centre " or a "divergent plate boundary."

8. Plate Tectonics

9. Here is the link : https://youtu.be/3ZpDjdFzQUM

10. Recapping The plate tectonics happened due to the conventual currents that happened due to the transmission of the heat restored in the core after it the mantle Plate tectonics got 3 different types : 1- CONVERGENT plate boundary 2- TRANSFORM plate boundary 3- DIVERGENT plate boundary

11. Convergent Plate Boundary Continental crust and Continental crust , this forms high mountains like Himalaya Mountains which happened due to the Collison of 2 continental plates ( Eurasian and Indian plates ) Continental crust and Oceanic crust , this forms subduction zones where these zone happens due to Collison of a continental crust with an oceanic crust making the oceanic crust bulks under the continental crust because oceanic crust got high density , this results in volcanos in the sides of the continental crusts . Oceanic crust and Oceanic crust , this forms island arcs where this formed due to the Collison of 2 oceanic crusts , one of them will buckle under the other forming these arcs ( orogeny )

12. Divergent Plate Boundary Continental crust and Continental crust , this forms the rifts we see in the deserts where this happens due to the diverges of both of 2 continental crusts . Oceanic crust and Oceanic crust , this forms the rifts in the sea where this happens due to the diverges of both 2 oceanic crust . Transform Plate Boundary Happens when the 2 slides transform from each other as u can see in the video .

13. Crustal Evolution The oldest known rock on Earth is about 4.1 billion years old. It is a granodiorite from Canada’s Northwest Territories. It formed below the surface as an igneous rock. Its chemistry is somewhere between that of granite and diorite . Granodiorite is usually formed at subduction zones . As illustrated in the video and in #11 , when 2 plates collides together , they forms island scars When plates joined together it is called accretion Southwest Greenland contains the oldest preserved crust of a continental landmass. It is 3.8 billion years old. It is Earth’s oldest surviving accretionary orogen . Here, oceanic lithosphere was subducted, and new continental crust was produced. However, it is highly fragmented and metamorphosed. This makes it difficult to study.

14. What is Orogen ? a linear or arc-shaped region that has been subjected to intense folding and other deformation during the tectonic cycle.

15. Continental collisions result in subduction that melts the leading edges of plates . As a result, andesitic magma forms. This type of magma has a lower density than surrounding crustal rocks. It takes the circular to oval shape this make it less dense and thick. This increases the buoyancy which is the ability of the body to float in certain areas They remain on the surface where they are subjected to billions of years of erosion . The thicker crust is also better insulated from the upper mantle and becomes more stable. These areas of the crust form continental shields .

16. What is Continental Shield ? Continental shield is a group of rocks that was the initial rocks during the young Earth , they say that the old of the rocks of shields is older than 3.7 billion years . They formed the roots of continents besides that makes the Earth’s surface stable . They were produced due to the plate tectonics and erosion , it was formed from Precambrian crystalline rocks . They commonly have a gently convex surface and are surrounded by sediment-covered platforms. One of rocks surrounding shields is greenstones

17. Greenstones They are rocks formed around the shields . They are green colored metamorphic rocks formed from dark igneous rock that often occurs in belts within Precambrian shields There name comes from the green mica-like minerals they contain . Belts of greenstone contains metamorphosized lava flows and sediments from chains of volcanic island . Volcanic island is often meant to be between island arc and the colliding continent Shields have grown by the addition of rocks , these rocks contain dark minerals and basaltic compositions from the sea floor .

18. Their mineral composition is controlled by the chemistry of magma . It also depends on the temperature at which the magma cooled. One of the most unique greenstone belts in the world is called The Barberton Supergroup . Supergroup is a very large stratigraphic unit consisting of many important smaller groups .

19. Greenstone Belts Plumes of granodiorite are common in greenstone belts. They cause shields to dome upward. Trapped between the rising domes, the greenstones became strongly folded and metamorphosed. A high-grade rock was formed due to the strongly folded and metamorphized shield which is GNEISS . At the same time , high domes was formed from ancient blocks of crusts with greenstone-granodiorite-granite which we call craton . From that we could differentiate between the old and later formed continental crust .

20. What is Craton ? a large stable part of continental crust that has undergone little deformation for a long period. Shields is considered as Cratons . A craton is an old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for at least 500 million years. Some are over 2 billion years old. Cratons are generally found in the interiors of continents and are characteristically composed of ancient crystalline basement crust of lightweight felsic igneous rock such as granite. They have a thick crust and deep roots that extend into the mantle beneath to depths of 200 km . More information about BASMENT CRUST IN #28

21. Diagram showing how greenstones was formed :

22. Weathering and Rock Cycle Three-billion-year-old sedimentary rocks form the top part of the Barberton Supergroup. The rock is about 2.5 km thick. These rocks indicate that Earth’s young, very small continents were subject to weathering and erosion. At this time , there was no soil or plants on land . The atmosphere had yet to develop free oxygen . It was mostly water vapor, carbon dioxide, and nitrogen . The atmosphere back then was more powerful at decomposing rocks than today. The surfaces of the young continents were rapidly stripped of weathered particles which means that there wasn ’t any weathered particles all of them was decomposed .

23. Rains washed their rocky surfaces. Sediment was transported by rivers. It was deposited around the edges of the continents . Coarse sediments were deposited in shallower water. They formed conglomerates and sandstones. Ripples and bedding structures also formed. They were like those seen in the ocean today. Ripples are sedimentary structures , it is the same shape when you throw a rock in the water , the rock will move away from its point of its entry in a circle or ring shape . These shapes always happens in high current flow of water . Finer sediments were transported into deeper water . They formed mudstone .

24. a) Ripple marks b) Bedding structure

25. Development of Magnetosphere The loss of heat from Earth’s exterior allowed its interior structure to develop. As molten iron solidified, it created the dense, solid inner core at the centre of the planet. The core has remained solid because of enormous pressures . The outer core is liquid . Motion in the iron-rich outer core continuously generates electrical currents. Because of rotating the magnet through an electric field , a magnetic field is formed , this is the same way in the Earth’s core . It is called geodynamic effect , it is self-sustaining which means that it could maintain itself . The magnetic field shields Earth from the solar wind . Without the magnetic field, the constant stream of particles from the Sun would have eroded Earth’s atmosphere. It would be lost into space. When igneous rock cool , magnetic mineral record the direction and strength of the magnetic field . Earth’s magnetic field moves in complex patterns where they identified that the magnetic dipoles changed its poles many many times . The last time it reversed its poles was 780,000 years ago .

26. The Development of North American continent Large fragments of the crust are called terranes . The various terranes of the North American continent show how continents grow largely by accretion. The huge continental mass is the North American Craton. Its basement , like the oldest rocks in most continents, is now covered by younger sedimentary rocks . Drilling through the crust reveals various basement rocks. These rocks vary in age. Each terrane was added by being welded to the continent during the process of subduction.

27. What is Terranes ? a region of crust added to a craton from a tectonic plate as a result of accretion (joining of 2 plates) . Terranes vary greatly in composition. In general they are made up of blocks of oceanic crust (basalts and greenstones) and overlying sedimentary rocks (limestones, cherts, shales, and sandstones) What is Basement crust ? The lowermost units of rocks that was happened due to the splitting of the continents and making it more stable . The units are often igneous and metamorphic.

28. The few slides coming after is cropped images from Earthcomm for the illustration of the Formation of Appalachian Mountains please pay attention to them !!!

29. The Appalachian Mountains formation The Appalachian Mountains formed when the rocks were trapped in the basins between the North American and African continents. The rocks were squeezed together to fold and fault . Intense deformation produced high-grade metamorphic rocks . This is one way that crust is welded to a continent by accretion along its margin. The Appalachian mountain chain continues northward into Nova Scotia. Other parts of the chain were separated by the opening of the Atlantic Ocean. They are found in Ireland, Western England, Scotland, and Norway. The young Appalachians may have been as high as the Himalayas are today . The mountains have since been worn down by erosion . As the mountains are eroded, the debris is transported by rivers to the coast. The terrane becomes buried by a thick sedimentary cover. The sedimentary deposits cause the continent to grow more in size.

30. The Development of the North American Cordillera The western edge of North America was also built up by a succession of accreted terranes. They are the youngest of the major tectonic units of the continent. They are less than 500 million years old. The accreted terranes on the West Coast are made of sediments. Coast are made of sediments . These sediments were scraped off the subducting Pacific Ocean crust. This took place as the oceanic crust was thrust under the North American Plate.

31. Enrichment Information !!!!! The Pacific Northwest was not always a subduction zone. Prior to the Triassic Period, North America was part of Pangea. At that time, the coast of North America was along the west side of Idaho. Pangea split apart 225 to 200 million years ago. As it did, North America began to move west into the neighbouring oceanic plate. New terrane was welded onto the west coast of the continent by accretion. Subduction formed volcanic mountains. Also, stresses in the crust folded and faulted rocks to form mountain ranges.

32. Geologic Province of North American coast 🡪🡪🡪🡪🡪🡪

33. subduction resulted in a huge amount of magma. This magma rose to the surface. Different generations of coarse-grained, pale granitic rocks were added to the crust . This took place for more than 100 million years. Scientists think that around 90 million years ago, the zone of accretion shifted west to the coastal ranges. T h e supercontinent called Gondwanaland split . It became Europe, Asia, North and South America, Africa, Australia, and Antarctica. As the crust thinned and rifted, huge outpourings formed continental flood basalts .

34. What is Flood basalts ? accumulation of mostly horizontal basalt formed by multiple eruptions from fissures. Flood Basalts are high volume eruptions that flood vast areas of the Earth , covering broad regions with flat lying lava surfaces. They are said to be the result of mantle convection through hot spots , which occur sporadically in time and place. Basaltic lava has a low viscosity. It may have flowed at speeds of 5 km/h. Sections of this gigantic deposit reached 190 km in length. The overlying mass of gigantic sill of basalt caused the crust to subside. It formed the Columbia Basin (Plateau).

35. Seismic Anatomy Map

36. The figure illustrated above , shows the seismic velocities of the North American continent . Blue colored areas are the areas with low velocities. Red colored areas are the areas with high velocities. If you stand in active subduction zone , the seismic velocity will be higher .

37. Geosphere , Hydrosphere , Atmosphere and Biosphere

38. Please pay attention to watch this 12 minutes video : https://youtu.be/6LkmD6B2ncs

39. LO 10 : The release of gases from earth’s interior

40. Gases and liquids in Mantle rocks Everyone of us must observed that when you open a carbonated beverage (Coca-Cola) which contains dissolved gas in it , the gas flow away this is the reason for the reduction of pressure . The reason you do not see bubbles in an unopened bottle is because the pressure of the outside of the bottle restricts the movement of the gas in the liquid . This prevents the gas from escaping . Heating the opened bottle increases the rate at which the gas escapes. There are some gases dissolved in earth’s hot mantle which are: carbon dioxide, nitrogen, and water vapor.

41. Mantle is subjected to very high pressures , this pressure could range between 250,000 to 1.7 million times of the atmospheric pressure . This high pressure make the dissolved gases (carbon dioxide , nitrogen , water vapor) remain in equilibrium in their environment . Remember the example of the carbonated beverage During volcanic activity, molten rock rises through the crust. The environmental conditions change. As the depth below the surface decreases , the mass of the overlying crust decreases . Therefore, the pressure on the rising magma also decreases . With a decrease in pressure, gases dissolved within the magma are released .

42. Earth’s rocky lithospheric plates contain special minerals. These minerals can hold water within their crystals. Mineral matter in Earth’s mantle also contains water. According to several experiments done by scientists in Japan in order to know about th e relation between the pressure and the ability for crystals to carry water in it , They found that at this great pressure the rocks in the mantle are able to contain huge volumes of dissolved water vapor. There is debate that the mantle contains volume of water greater than all the water in Earth’s ocean .

43. Many crystals in Earth’s crust begin to form in some kind of fluid. As these crystals grow, they often trap tiny bubbles of the fluid . This provides important information about the conditions under which the crystals formed. By heating the bubbles, scientists can find the temperature and pressure at which the crystals formed. One instrument used for this was designed by the USGS . It is extremely sensitive. It is capable of detecting amounts as low as 8 parts per billion in samples as small as 0.01 mm in diameter.

44. A microscopic fluid inclusion within a quartz grain

45. Gases dissolved in Earth’s mantle are released into the atmosphere during volcanic eruptions. These can occur when a plate descends downward into the mantle. The plate can get so hot that any water or gas it contains rises into the overlying mantle. The overlying mantle melts into magma. The magma is less dense than the solid rock that surrounds it . It then rises through the mantle to the overlying crust. As it nears Earth’s surface, there is less overlying rock. The pressure on the magma decreases. At the surface, the magma is under atmospheric pressure. Gases such as carbon dioxide, nitrogen, sulphur dioxide, and water vapor dissolved in the magma are released into the atmosphere . Various volcanic processes release dissolved gases from Earth’s mantle. These include continental and oceanic volcanic eruptions, outpouring of lava flows, and rifting. Also included are rising plumes at hot spots and at mid-ocean ridges. During these processes, hot material from the deep mantle reaches Earth’s surface. As this takes place, any dissolved gases it contains are released.

46. Plate which descends down

47. The Evolution of Earth’s Fluid spheres Earth’s interior has been releasing gases since its formation 4.6 billion years ago. These gases were trapped within the solid rock particles that came together under the influence of gravity to form Earth . Over time, Earth mas increased by more and more rocky debris was pulled in from the solar system. As Earth’s mass increased, its gravity grew. The pressure increased on its interior , then its interior heated and melted. Meteorites bombarded the surface of the young Earth. This caused its primitive crust to melt and rift. As this occurred, large amounts of gases were released through fissures in Earth’s surface. As this occurred, large amounts of gases were released through fissures in Earth’s surface.

48. Earth’s gravity kept these gases from being stripped away by the solar wind and blowing off into space. The process by which huge volcanic eruptions transfer matter from the mantle to the atmosphere is called outgassing .

49. Outgassing The release of gases from Earth’s interior that formed the primordial atmosphere and continues today. Outgassing early in Earth’s history produced primoradial atmosphere (largely water vapor and carbon dioxide). There were also lesser amounts of carbon monoxide, hydrogen, and hydrogen chloride. In contrast to the atmosphere today, oxygen was mostly absent. During the early Hadean, Earth’s surface temperature was extremely hot. It was too hot for water to exist as a liquid at the surface . As a result, there were no oceans, lakes, rivers, or groundwater.

50. As the young Earth cooled, outgassing formed a new atmosphere. It is consists of (methane, hydrogen, nitrogen, and water vapor, with smaller amounts of noble gases and carbon dioxide). Noble gases like helium. Earth’s cooler surface radiated less heat into the atmosphere. Further cooling enabled water vapor to condense . It fell to the surface as rain . Much of the first rains would have fallen on hot volcanic rock and evaporated. As the crust cooled more, rain began to collect in low-lying areas. This formed bodies of water on the surface. Eventually, enough water was released from Earth and condensed to form the world’s oceans .

51. ` On the primitive continents, Earth’s first river networks formed. The rivers flowed and transported rock particles worn from the continents. These sediments built up in the oceans. They formed early marine sedimentary rocks . The outgassing of carbon dioxide produced rainfall and oceans that were more acidic than today: Because carbon dioxide, when combined with water, forms carbonic acid. For instance the pH of early Haden ocean 5.8 and the pH of the ocean now nearly 7. Some of the dissolved chemicals would later become limestone and the shells of marine organisms. Today, the oldest organic marine limestones are found in western Australia. They are in rocks 3.5 billion years old.

52. Formation of oceans and atmosphere Some scientists believe that the process of outgassing did not form the atmosphere and oceans. They argue that the young Earth’s gravity pulled in chemicals released by the Sun. Other scientists think that Earth’s water came from gigantic comets several kilometers long, passing by Earth. They suggest that Earth’s gravity pulled in ice and rocky material from these comets .

53. Interaction between Fluid Sphere and Young Earth Many scientists believe that Earth’s young atmosphere was richer in greenhouse gases . This kept the planet from freezing over. As the Sun became brighter, the concentration of greenhouse gases declined. They eventually reached modern levels . This is known as the faint young Sun paradox. The interaction between the geosphere and the fluid spheres was very important to the development of the granite rocks that now make up the continents .

54. Earth’s young crust was largely made of basalt weathered from the crust had more silica . Silica is resistant to chemical and physical attack. Silica-rich sedimentary rocks built up in the oceans. They later melted in subduction zones. As a result, the melted basaltic oceanic crust became richer in silica from the added melted sedimentary rocks.

55. Fluid Spheres on Other planets and Moons Earth is not the only planetary body in the solar system with fluid spheres. Venus and Mars both have atmospheres. Like Earth. The mass of Earth’s atmosphere is about 100 times greater than Mars. It is 100 times less than that of Venus. One of Jupiter’s moons, Io, has an atmosphere that is strongly affected by the Jupiter’s gravitational field. Europa, another of Jupiter’s moons, has a thin oxygen-rich atmosphere. Titan, Saturn’s largest moon , is icy and rocky . It has an atmosphere rich in nitrogen with clouds of methane.

56. Earth’s fluid spheres are unique among the other planets . Earth is the only planet with abundant free oxygen . Venus and Mars also have oxygen, but it is tied up in carbon dioxide molecules. Earth also has abundant water in all three states

57. Questions

58. LO.11: The Biosphere and The Evolution of The Atmosphere

59. How scientists detected the Early Atmosphere ? It is easy to understand that scientists couldn’t directly sample the Earth's early atmosphere from billions of years ago . Instead , they looked for clues , Some of these clues are in the chemistry of rocks , most of these rocks were formed in the ancient marine environment . Iron oxide is one compound in these rocks where scientists knew about the early atmosphere from where it told them the amount of oxygen in Earth’s ancient atmosphere .

60. Iron Oxide It is an Inorganic chemical compounds composed of iron and oxygen . Many varieties exist, including the minerals magnetite (Fe 3 O 4 ) and hematite (Fe 2 O 3 ). Oxidation is the combination of a substance with oxygen . Iron oxidized, or combined with oxygen, to form iron oxide. This process usually happens in water .

61. If you put an iron tablet in a beaker of tap water , You most likely observe the water change to reddish brown as the iron tablet dissolved. Gradually, reddish-brown particles formed in the water. This gave it a cloudy appearance . As more iron combined with oxygen, larger and larger iron-oxide particles formed. They sank to the bottom of the container. This removed the iron from the solution . If you do not add new iron, the concentration of iron in the solution decreases thus if you left the water for few days and then come back you will find that water came back to its original appearance . Paint or rust proofing is used to protect the iron in these items from rusting. They prevent the iron from coming into contact with moisture and oxygen. This prevents iron oxide from forming.

62. Banded Iron Formations a sedimentary rock made of tiny quartz crystals formed from watery solutions rich in silica , often grey in colour. Chert rocks, more than two billion years old, that consist of oxides, sulfides , or carbonates of iron, thinly interbedded with chert , a silica rich rock. they were made up of alternating dark and light layers of rock . Some of the layers contain iron-rich minerals . The minerals are hematite and magnetite which are common.

63. Example for Branded Iron Formation Example for Chert

64. Branded Iron Formations are commonly associated with greenstone belts . They were moved onto the continents by accretion . Accretion is the process by which the cores of ancestral continents grew by the subduction of adjacent oceanic crust and the welding of crust to the continental margin which means that accretion happens when there is island arc in the oceanic crust and at the same time the oceanic crust is being subducted by the continental crust so that island arc resist the oceanic crust to be subducted resulting in the accretion of the both of the plates . Scientists think that during the late Hadean the oceans contained vast amounts of iron and silica . One source of the iron seems to have been underwater volcanoes . The iron was released in fluids from hydrothermal vents . There, the material from the upper mantle mixed with seawater

65. Another source for the iron and silica in the oceans was Earth’s crust . Earth’s young basaltic crust was rich in minerals that contain iron and silica. Earth’s new crust was exposed to the warm primitive atmosphere. This caused rocks to weather. The weathering process released iron and silica from the crust. They found their way into rivers in solution and in mineral fragments. The rivers eventually deposited the iron and silica into the oceans. Iron was being added to seawater for several hundred million years. However, it was not being removed. Also, at that time, there were no organisms that required silica to form shells. As a result, the ocean water became saturated with silica as well . Iron and silica are the chemicals found in the iron-rich and chert layers that form banded iron formations

66. How banded iron formed ? Between about 3.5 and 2 billion years ago, the iron and silica began to react with oxygen dissolved in Earth’s ancient ocean. Iron reacted to form iron-oxide minerals. They built up in layers on the ocean bottom . Silica in the water also reacted with the oxygen. As a result, layers of silica-rich chert were formed. Some scientists think that the layering of banded iron formations reflects the competing influences of hydrothermal processes and continental fluxes of material where volcanism released iron and silica

67. From where did oxygen come from ? Scientists thought that the oxygen must have come from ancient cyanobacteria . Recall that cyanobacteria are phototrophs . They use photosynthesis to convert energy from the Sun into food. Oxygen is a by-product of photosynthesis. The population of cyanobacteria on Earth increased. As a result, 3.5 to 2.5 billion years ago, more and more oxygen was released into Earth’s atmosphere. Cyanobacteria is considered the first prokaryotic cell to be formed

68. The atmosphere and oceans readily exchange gases . As the oxygen content of the atmosphere increased, the dissolved oxygen content of the surface waters in the oceans also increased. Oxygen reacted with the dissolved iron and silica in the ocean. This resulted in the layers of the banded iron formations. Until 2.3 billion years ago, oxygen was drawn down into the oceans . It replaced oxygen used up in forming the banded iron formations. This kept the concentration of oxygen in the atmosphere to low levels. The levels were 1–2 percent of what they are today. the deposition of banded iron formations began to slow down. There was less and less dissolved iron in the oceans . The rate at which iron was resupplied to the oceans had decreased. By 1.8 billion years ago, there was very little dissolved iron in ocean water. The banded iron formations stopped forming altogether.

69. The cyanobacteria flourished. They continued to produce oxygen. However, the iron was no longer there to act as a sink for oxygen in the oceans. Less oxygen was drawn from the atmosphere into the oceans. As a result, oxygen began to build up in the atmosphere. The soils indicate that atmospheric oxygen at the time was 15 percent that of the modern level. Current levels of oxygen were reached probably about 600 million years ago . Along with a buildup of oxygen, came an increase in ozone levels (O 3 ). The increase in oxygen and ozone had important implications for life on Earth. Ozone absorbs much of the UV radiation that strikes the atmosphere. It formed a protective layer around Earth. This made the continents a more hospitable area for organisms to live.

70. Questions

71. LO 12,13 : Geologic Times

72. What is Geologic Time ? It is the interval of time since the formation of Earth and there is a scale for it . The geologic time scale is the division of geologic time into units based on evolutionary events of geologic history . Some parts of Earth had more unique events than others. Some events occurred only once in Earth’s past. As The formation of Earth , The development of the core , The mantle , The crust occurred , Development of the atmosphere . Other events are cyclical . Mountain formation , The eruption of volcanoes , and Earthquakes , which means that it forms regularly in repeated cycles . In order to detect the geologic time scale , scientists begun to use the history of the biosphere .

73. What is Biosphere ? It is relatively thin life-supporting stratum of Earth’s surface, extending from a few kilometres into the atmosphere to the deep-sea vents of the ocean . The biosphere is a global ecosystem composed of living organisms (biota) and the abiotic (non-living) factors from which they derive energy and nutrients . Fossils lies in the biosphere . Fossils are evidence of once-living things . These organisms are preserved in sediments and rocks . Fossils indicate when Different species of organisms have appeared and disappeared over time. Extinct species do not reappear later. Scientists use the arrival and extinction of different fossils as markers.

74. Eons The longest unit of time and division of geologic time that contains two or more eras . So far, there have been four eons . Each has its own unique story. The Hadean Eon is the first part of Earth’s history. This part of Earth’s history lasted 800 million years . During this time, the Moon formed , and meteorites bombarded the geosphere . Toward the end of the Hadean, simple life had gained a foothold on Earth.

75. Scientific Notation for Geological time Using the scientific notation for geological time, that is 1 Ma for mega annum or millions of years 1 Ga for giga annum or billions of years

76. More Eons The Archean Eon , lasted from 3.8 to 2.5 Ga . It contains evidence of early cellular life and photosynthesis . Next came the Proterozoic Eon 2.5 Ga–542 Ma . It is marked by the appearance of early life forms . However, it was the time before abundant life. The First major glaciation (Formation of glaciers) took place 2.3 Ga . Presently, Earth is in the Phanerozoic Eon . It has lasted about 542 million years so far. It is a time of abundant life. This is about an eighth of geologic time. During the Phanerozoic Eon , evolution has led to large-scale changes in the biosphere. Scientists have used these to further define the geologic time scale.

77. Hadean Archean Proterozoic Phanerozoic

78. Eras Eons are divided into shorter units of time called eras which is a major division of geologic time that contains two or more periods. The Phanerozoic Eon is divided into three eras. The Paleozoic Era is the era of ancient life . It lasted about 290 million years . The Mesozoic Era is the era of middle life . It lasted about 185 million years. The Cenozoic Era is the current era of modern life . It has lasted about 65 million years so far.

79. Changes in the mix of animals and plants in the biosphere define the beginning and end of each era. For example, the Mesozoic Era is called the Age of Dinosaurs. It ended when most of life on Earth became extinct . The next is called the Cenozoic Era . It included the evolution of mammals. Many of these mammals live on Earth today .

80. Periods Eras are divided into shorter units of time called periods . Each period is named by the scientists who discovered it . Sometimes the names are from a particular region like the Cambrian, Ordovician, and Silurian are names of three periods . They are named after Welsh tribes . Each period lasts tens of millions of years . They subdivide geologic time in a way similar to how hours divide a day. Each one also tells a unique part of Earth’s history. For example, the Cretaceous Period was when large dinosaurs were abundant . It lasted about 80 million years . After the Cretaceous Period ended, the number of dinosaurs decreased. A new period began. This was called the Paleogene Period . Scientists have defined this period according to the appearance of a large number of mammal fossils.

81. Epoch It is part of the geologic time scale . That help define time even more precisely. This is much like minutes within an hour . Epochs are often determined by special events in other parts of the Earth system.

82. Dating Rocks by using Radioactive decay Scientists use geologic evidence for many events in Earth’s history. Mountains provide evidence of plate collisions or volcanic activity . The shields that form each continent tell about how Earth’s crust evolved. Special iron-rich rocks formed in the oceans tell about how the atmosphere was formed. Changes in fossil groups indicate changes in past climates. Younger layers of sediments are deposited on top of older layers . This gives a relative age of a layer of rock . You can identify a rock layer as being younger or older than the layers next to it. Relative age: a date given for a sample expressed as younger than or older than another rock or fossil.

83. Knowing the exact ages of rocks helps them to unravel further some of the secrets of Earth’s history. It can help them to answer questions like: - 1-How old is Earth? 2- When did the first continents form? 3-How long does it take for ocean crust to be recycled in the mantle? To determine the absolute age of a rock, scientists look for radioactive minerals. Absolute age: a date given for a sample expressed in years. These minerals contain radioactive elements. The nuclei of these elements are unstable. As a result, they break apart over time. This process is known as radioactive decay. Radioactive decay : the process by which an atomic nucleus of an unstable atom loses particles

84. As particles are released, the original element changes into a different one. The new element has slightly lighter properties. The atom that undergoes decay is called the parent atom . The product is called the daughter atom. Parent atom is the atom that undergoes radioactive decay in a nuclear reaction. Daughter atom is the product atom from the radioactive decay of a parent atom.

85. Scientists look at the rate at which a radioactive element in a mineral decays to determine the age of the rock in which it is contained . The time it takes for half of the parent atoms to decay into daughter atoms of a different element is called a half-life . Half-life : the length of time it takes for half of a radioactive substance to decay Knowing the half-life of an element and the fraction of parent atoms left, a decay graph is used to determine when the parent atoms were fully intact. The date when the rock was formed can then be determined. Example for decay graph :

86. The radioactive isotope of rubidium has a very long half-life. It takes about 48.8 billion years for half of it to change to strontium . Elements such as this, with very slow rates of decay, are good for finding the ages of very old rocks . Using radioactive decay , scientists have found Earth’s oldest mineral to be zircon Zircon contains small traces of the radioactive element uranium . (Uranium decays to form lead.) Zircon samples have been found that date as far back as 4 billion years. Zircon is highly resistant to weathering and erosion .

87. Zircon

88. Radioactive Dating Radioactive dating is done mostly on igneous rocks . Radioactive elements are trapped in certain minerals when magma cools and hardens to form rock. There are a few types of sedimentary rocks that contain radioactive elements. The radioactive “clock” is reset in new minerals that form when rocks are deformed. These minerals give a younger age for the rock than when it originally formed.

89. Radiocarbon Dating Radiocarbon dating is used to find the age of once-living materials between 100 and 50,000 years old. This range is especially useful for determining ages of human fossils and habitation sites. The atmosphere contains three isotopes of carbon: carbon-12, carbon-13 and carbon-14 . Only carbon-14 is radioactive , it has a half-life of 5,730 years. The amount of carbon-14 in the atmosphere is tiny and has been relatively stable through time . Plants remove all three isotopes of carbon from the atmosphere during photosynthesis . Animals consume this carbon when they eat plants or other animals that have eaten plants. After the organism’s death, the carbon-14 decays to stable nitrogen-14 by releasing a beta particle. The nitrogen atoms are lost to the atmosphere, but the amount of carbon-14 that has decayed can be estimated by measuring the proportion of radioactive carbon-14 to stable carbon- 12 . As time passes, the amount of carbon-14 decreases relative to the amount of carbon-12.

90. Potassium-Argon dating Potassium-40 decays to argon-40 with a half-life of 1.26 billion years. Argon is a gas so it can escape from molten magma, meaning that any argon that is found in an igneous crystal probably formed as a result of the decay of potassium-40. Measuring the ratio of potassium-40 to argon-40 yields a good estimate of the age of that crystal. Potassium is common in many minerals, such as feldspar, mica, and amphibole . With its half-life, the technique is used to date rocks from 100,000 years to over a billion years old. The technique has been useful for dating fairly young geological materials and deposits containing the bones of human ancestors.

91. Uranium-lead dating Two uranium isotopes are used for radiometric dating. Uranium-238 decays to lead-206 with a half-life of 4.47 billion years . Uranium-235 decays to form lead-207 with a half-life of 704 million years. Uranium-lead dating is usually performed on zircon crystals When zircon forms in an igneous rock, the crystals readily accept atoms of uranium but reject atoms of lead. If any lead is found in a zircon crystal, it can be assumed that it was produced from the decay of uranium. Uranium-lead dating is useful for dating igneous rocks from 1 million years to around 4.6 billion years old . Zircon crystals from Australia are 4.4 billion years old, among the oldest rocks on the planet.

92. Questions: (these slides are animated make sure to get in the Fullscreen mode)

93. LO 14: The fossil record

94. Food Chains and Food Webs: Plants use energy from the Sun to make food through the photosynthesis process . Producers are the organisms that make their own food. Consumers are the organisms that rely on plants for food to obtain energy. The food chain is a kind of flowchart to show how organisms are connected to each other by the food they eat. It shows how energy and matter are transferred from producers to the next levels of consumers.

95. The relationships between organisms are shown in the form of a food web . (as shown in the figures) Decomposers are a special group of consumers who obtain the matter and energy they need from wastes and dead plants and animals.

96. Fossils: Fossils are any evidence of past life preserved in sediments or rocks. There are two types of fossils: 1- Body fossil 2- Trace fossils 1-Body fossils: They are any remains or imprints of actual organic material from a creature or plant that has been preserved in the geologic record (Bones, teeth, shells, and other hard body parts). Dinosaur bones

97. For the specific conditions, the fossil record of soft-bodied organisms is far less well known There is a strong bias in the fossil record. Some organisms rarely have the chance of becoming fossilized. Under very specific circumstances, however, even these can become part of the fossil record. Bias is a purposeful or accidental distortion of observations, data, or calculations in a systematic or nonrandom manner Jellyfish fossil They may become broken, worn, or even dissolved before they might be buried by sediment. Soft bodies organisms are hard to preserve unless under specific conditions (such organisms fall into a muddy sea bottom in quiet water and are fossilized)

98. 2-Trace fossil: It is a fossilized track, trail, burrow, tube, boring, tunnel or other remnant resulting from the life activities of an animal. Trace fossils are useful for geologists and paleontologists because certain kinds of organisms, which live in specific environments, make distinctive traces. Paleontologist is a scientist who studies the fossilized remains of animals and/or plants. Feeding trails and burrows

99. young sediments and rocks, the actual body parts of an organism are often preserved. In older rocks, the body parts are usually dissolved away, recrystallized or replaced by another kind of mineral but the imprints are still preserved which can be studied if the rock splits apart in the right place and the right orientation . Scientest collect rocks and put them on special mechanical splitting devices to try to find at least a few fossils.

100. Fossilization: only a very small part of what once lived is spared being a meal for some other organism. any organism on Earth will be either consumed by another organism or decomposed by microorganisms following death. Decay affects soft body parts and some of the harder, more resistant body parts. Each plant and animal that lives in the forest eventually ends up on the forest floor in some form.

101. Soft tissues of animals, leaves, and flowers are used by decomposers as they decay within several weeks or are used by some other organism as a food source. The most resistant body parts (insect exoskeletons, vertebrate bones, wood, leaf cuticles, seeds, pollen, and spores) may remain on the forest floor for many years or even centuries depending upon the physical and chemical conditions of the soil.

102. For an organism or body part to become a fossil, certain conditions must occur. It must either live within or be moved to a place where it can be buried. However, being buried does not guarantee that a fossil will form. all organisms will decay but there must be other factors at work during or right after burial to slow or stop decay. The conditions necessary for fossilization do not exist everywhere all of the time but only in a few places and for only a tiny bit of the time.

103. huge numbers of organisms have become fossilized because of the extent of geologic time. It is difficult to imagine how long a million years is. Yet physical, chemical, and biological processes have been operating on Earth not just for millions of years, but for billions of years. The geologic time scale. It indicates when various kinds of organisms are first seen in the fossil record.

104. https://youtu.be/sC9iqGb94hc This Video May help you in memorizing the geologic time scale illustrated above

105. Fossilization rocks: Fossiliferous : A rock that contains fossils. Not all sedimentary rocks contain fossils. Some kinds of sedimentary rocks contain more fossils than others. Limestones are the most fossiliferous sedimentary rocks as they are made up in part, or entirely, of the body parts of shelly marine organisms. Fossiliferous limestone

106. Some shales are fossiliferous as well because certain organisms like to live on muddy seafloors. Sandstones usually contain much fewer fossils than limestones. Fewer kinds of organisms can tolerate the strong currents and shifting sand beds that are found in areas where sand is being deposited. For the same reason, conglomerates are the least fossiliferous of sedimentary rocks.

107. LO 15: Mass Extinction

108. Textbook: EarthComm chapter 8 section 9

109. The Extinction of Species It is impossible to predict the success or failure of one species . Many physical and biological factors interact in complicated ways , all these factors determine the success or failure of a species. Also, the data from the fossil record seem to indicate that different kinds of organisms have different rates of success. It is found that there are species that lasted for tens of millions of years , others lasted for hundreds of million of years . Other life spans for species only lasted for a few million years. The 2 main reasons for Extinction are loss of habitat and loss of genetic variation

110. The Extinction of Species at the end of Mesozoic There was big difference in the landscapes of the Mesozoic Era and the Cenozoic Era. (The terms come from the Greek meso- , meaning middle and kainos- , meaning new.) The group of animals that dominated the Earth for nearly 130 million years during Mesozoic suddenly became extinct , the extinction process mostly took place almost overnight. This sudden extinction affected some plants and many groups of animals that lived on land . It affected much of the food web in the oceans as well. Groups from phytoplankton to top carnivorous disappeared from fossil record , they were never be seen again except as a fossil material.

111. Phytoplankton are small photosynthetic organisms, mostly algae and bacteria, found inhabiting aquatic ecosystem. Carnivorous are an organism that eats mostly meat, or the flesh of animals, sometimes carnivores are called predators. The post boundary biosphere was very different in nature. It was established early in the Paleogene. It took several million years for the plant and animal groups known to exist now to evolve. It took a long time to fill all the ecological spaces opened by this extinction event. The Paleogene is one of periods in tertiary period of Cenozoic Era. The post-boundary fossil record shows that changes in the kinds of animals now extinct are linked to food source(s). They are related to the appearance and disappearance of these food sources.

112. The fossil record shows that when evolution comes and changes the make up of plants in a community, dependent organisms must find a new food source. They must change how they process food for nutrition as well. If they are not able to do so, they face extinction. Until the Mid- C enozoic, there was no evidence in the fossil record for grazing animals. About this time grasslands appeared . Following this, many new groups of animals are found for the first time in the fossil record. The diets of these animals include the plants of the grasslands like grazing animals . In North America, such animals include camels, rhinoceroses, and horses . Also included are many other mammals that are now known to be extinct. The extinction of a few species now and then appears to be a normal phenomenon. Scientists refer to the appearance and disappearance of a few species at any time as background extinction . Background extinction is normal extinction of species that occurs as a result of changes in local environmental conditions .

113. Biodiversity & Mass Extinction It is the diversity of different biologic species and/or the genetic variability among individuals within each species. Fossil record sometimes show a change in the biodiversity A mass extinction event is when species vanish much faster than they are replaced. This is usually defined as about 75% of the world's species being lost in a 'short' amount of geological time - less than 2.8 million years. The major types of diversities in the biodiversity are genetic diversity, species diversity, ecological diversity and functional diversity

114. There have been five major ones throughout the history of life. During these, up to 90 percent of the known biodiversity was lost. One such event took place at the end of the Palaeozoic Era. This was between the Permian and the Triassic Periods. it was more devastating to life on Earth than extinction at the end of Mesozoic. Geologic time is divided into the Palaeozoic, Mesozoic, and Cenozoic Eras. The specific places the time is divided and the time each era last has a reason. The reason is the size and abruptness of the extinctions.

115. Causes of Mass Extinction A scientist named Luis Alvarez and his colleagues proposed a hypothesis. It stated that the extinction was caused by the collision of a huge asteroid with Earth. They based this on studies of sections through sedimentary rocks. These rocks were found at the Mesozoic– Cenozoic boundary. In several sections, they found geochemical evidence. Where amounts of element iridium in this time was many times greater than normal amounts of the element iridium. The evidence pointed toward a catastrophic collision. Iridium is very rare on Earth’s crust. Large amounts of iridium are found on meteorites and comets. Therefore, the iridium was introduced into the Earth system during certain impacts.

116. Another Evidence of the collison Another important piece of evidence was found in the Yucatán Peninsula of Mexico. It was the remnants of a colossal impact structure. This structure is called the Chicxulub crater. The collision placed so much dust and ash into the atmosphere that the climate became much cooler. It is thought that light could not reach Earth’s surface. Earth’s ecosystems were stressed for a long time after the collision. This led to widespread extinction of many species. Evidence of sediment movement and deposition by a gigantic sea wave could be seen in the Gulf of Mexico. This evidence, likely caused by the impact, has strengthened the hypothesis.

117. Another Evidence There is also good evidence for increased volcanic activity around this time. A few scientists like an alternative hypothesis for the great extinction. It has to do with climate change induced by the eruption of the volcanoes. Evidence is still being gathered. There are still details to resolve about the extinction and its causes.