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Earth has four different spheres or domains that are affected by climate: atmosphere, hydrosphere, lithosphere, and biosphere.
Atmosphere surrounds the earth in layers:
- Lower atmosphere at ground level
- Troposphere from 20 km from earth
- Stratosphere from 40 kmionosphere from 60 km
- Outer space with no atmosphere.
Figure 1. Layers of Atmosphere
All life on earth depends on the atmosphere for protection of direct radiation from the sun, for supplying water, and for providing plants with the things they need to grow. The gases in the atmosphere participate in cycles. One of the most important is the Carbon Cycle since all of the organisms on Earth are carbon-based life forms.
- includes all water on the surface of the earth oceans, lakes, rivers, aquifers, and ice.
- 70% of the earth’s surface is covered with water.
Figure 2. Hydrologic Cycle
- covers the remaining 30%
- is between 0 and 40 km thick.
Figure 3. Layers of the Earth
- consists of igneous, metamorphic, and sedimentary rock that can be transformed through the rock cycle.
Mountains are formed and then continually broken down by the forces of erosion wind, ice, flowing water, plant roots, temperature changes, and chemical reactions.
The processes of erosion are balanced with the processes of mountain building folding, faulting, and volcanism on the earth’s surface and ocean floors. These processes are explained by the theory of plate tectonics.
- Where all life exists and includes the other three spheres the lower layer of the atmosphere, a few metres of the lithosphere, and all of the hydrosphere.
- Amount and diversity of the biomass depends on the distance from the equator. Generally, the closer to the equator, the greater the biodiversity. These plants are reservoirs for carbon, either in solid or dissolved form, as carbohydrates (sugar, cellulose), proteins, and oils.
The theory of plate tectonics addresses many questions about earthquakes, volcanoes, and mountain building, and the opening and closing of ocean basins.
Figure 1. Plate Tectonics
Six major plates and some smaller ones form the earth’s crust and hold the continents.These plates are constantly shifting resulting in collisions and separations due to convection currents in the mantle
Figure 2. Convection Current
Figure 3. Convection Current in the Mantle
Convection, like boiling water in a pot, happens within the upper mantle, bringing molten rock up from the asthenosphere to the lithosphere, and causing the plates to separate. It begins to cool and is pushed out of the way by the rising of new molten materials. As it cools further it is drawn back down to the mantle, causing the plates to collide. It reheats and moves back up replacing the rock that has started to cool and move out of the way.
Volcanoes and earthquakes occur when one plate overrides the other, causing the heavier plate to sink or subduct below the ocean floor into the mantle. There it becomes molten or mafic rock and rises to the surface of the ocean floor and begins to build a volcano which eventually will rise above sea level
Faulted mountains are created when one plate overrides the other, but instead of subducting, the leading edge of the plate breaks, is thrust upwards, and melds together in a new landform by the friction caused by the movement.
Figure 6. Types of Faults
Sometime the plates collide and crumple along their leading edges to form fold mountains. The surface of the earth has been constructed over a long period of time by global tectonic forces.
The lithosphere is divided into two parts ocean basins and continetal block cratons or plates. They are extensive solid slabs of rock that form the Earth’s crust or lithosphere. These large and small plates move in relation to each other over the molten material of the mantle that lies beneath.
ACTIVITY 1 Web Search
- View the Plate Tectonics animation: www.ucmp.berkely.edu/geology/tectonics.html
- Try an experiment on Mountain maker: do an internet search “A Science Odyssey: You Try It: Plate Tectonics” .
- To see all the continental reconstructions do an internet search for “Global Earth History” from NAU. Go to “Time Slice”.
Plate tectonics cause continental drifting in the lithosphere. As the plates drift, they either collide or move apart. Where they collide and one plate overrides another, fold or thrust-fault mountain belts are formed. Where the plates subduct, volcanoes are formed.
This is the process that influences the timing of ice ages and the positioning of continents. It is one of the most important factors controlling long periods of multiple glaciations. Large landmasses at the poles seem to be the trigger for the development of extensive ice sheets. This is because large accumulations of ice cannot form on the ocean. Landmass distribution or continental drift cause changes in the circulatory patterns of ocean currents. Whenever there is a large landmass at one of the Earth’s poles, ice ages occur.
Late Proterozoic Era
glaciation (around 700 million years ago) is not well known but evidence of glaciers in North America, Australia, and Africa exists.
Our present day continents started to form in the Paleocene Epoch of the Tertiary Period.
Panagea broke up into two continental landmasses – Laurasia in the northern hemisphere and Gondwanaland in the southern. They existed between the Triassic and Crustaceous Period.
Towards the end of the Paleozoic era the continents had started to come together and the formation of the supercontinent known as Pangea had begun.
Rodinia is thought to have included most or all of the Earth’s continents and to have broken up into eight continents around 600 million years ago. Rodinia was mostly tropical and was distributed between about 60o S and 30o N.
land masses were in micro continents, composed of cratons and orogens.
- What are the connections between a subduction zone and a ridge?
- What are the connections between a ridge and a plate ?
- What kind of mountain is built because of subduction?
- What two kinds of mountains are formed because of collision?
- What are the two parts the lithisphere divided into?
- Study the several reconstruction models of the continents by Ronald C. Blakey, NUA and notice how the continents have drifted. Identify:
(i) which reconstructions indicate supercontinents
(ii) which ones do notwhat climate each reconstruction would have and why.
Figure 10.CENEZOIC ERA
Figure 11. MESOZOIC ERA
Figure 12. PALEOZOIC ERA
Figure 13. PRE-CAMBRIAN ERA
Plate tectonics again contributes to the development of long periods with many glaciations in a second, more subtle way. Plate movements sometimes cause uplift of large continental blocks. Major uplift can cause significant changes in the oceanic and atmospheric circulation patterns. Changing circulation patterns cause climate change.
Over the past 15 million years, the continents have risen about 600 meters (2,000 feet) on average. The uplift of the Himalayas and the Tibetan Plateau contributed to the initiation of the current cool period. Other tectonic uplifts have been involved in the three other long ice age intervals. The average elevation of continents has doubled since the mid-Cenozoic. This results in a general drop in temperature (about 3 degrees) from the increase in elevation, and interferes with heat transfer from the equator to the poles via wind and ocean currents.
The current Pleistocene Glacial Epoch had it’s beginning about 3.2 million years ago and is linked to the tectonic construction of the Isthmus of Panama which prevented the circulation of Atlantic and Pacific waters and caused the beginning of a slow cooling of the atmosphere and the formation of new ice fields about 2.5 million years ago.
Figure 13 Mountain Building (Orogenesis)
The influence of mountains and plateaus reaches high into the stratosphere. The Late Cenezoic was a time of massive mountain building:
- Western North America
- Pacific margin of South America
- Rift system in East Africa
- Tibetan plateau and Himalayas
The Tibetan plateau and the Himalayas were caused by a collision between India and Asia. The 2 km uplift of the Tibetan plateau blocked the mid-latitude air flow. It also strengthened the monsoons and affected the entire northern hemisphere.
The climate change brought about by the uplift of the western North American and Tibetan highlands greatly altered the plant cover. The change in climate corresponds to the present situation and is sharply different from the conditions in the mid and low-latitudes during the Miocene and earlier.
ACTIVITY 3 Questions
- Consult an atlas and label the world mountain ranges on the map.
- Explain how the climate factors of the various regions have changed and justify your answer with supporting details (facts, data, visuals, etc.)
Figure 1. Circum-Equator Seaway Circum-Polar Seaway
Barriers and gateways play important roles in the circulation of the oceans. If the equatorial current can pass around the Earth one or more times before being deflected north and south, a more even heat distribution across the latitudes results. The Earth becomes warmer and wetter.
Some the equatorial current flow has been restricted. Gateways established at high latitudes allow circum-polar currents to pass. Circumpolar currents insulate polar continents from warmer seas and cause polar temperatures to drop.
Mesozoic: The surface circulation of the oceans evolved from a simple pattern in a single ocean with a single continent to a more complex situation in the new oceans of the Cretaceous. During this time, the open circum-equatorial path and the absence of circumpolar current resulted in a temperature distribution that was more even than today.
Cenozoic: Continental drift caused two major changes in ocean circulation:
a gradual change in ice-house conditions: the opening of the Antarctic circum-polar seaway 25-35 MY agothe final closure of the circum-equatorial seaway when Isthmus of Panama emerged in Pliocene.
ACTIVITY 4 Question:
Using the Ocean Circulation model sheet, for the Mesozoic and Cenozoic Eras:
- Describe the changes in the ocean current
- Describe the changes in the oceans.
- Describe the changes in the position of the continents.
- circum-equatorial seaway in place.
- warm water from the low latitudes warmed the waters in the higher ones.
In the middle Oligocene 30 MBP the warm water flow to high latitudes further diminished because
Tethys Sea slowly closed and the Drake passage opened. Now the Circum-Antarctic Current developed. The circling waters insulated the polar continent from warm low latitude waters. The Antarctic icecap developed further and the Arctic Ocean gradually closed in when North America and Eurasia drifted northward. Arctic sea ice appeared for the first time and the sea-level steadily dropped.
By early Miocene, ocean basins and surface currents resembled those of today. The Antarctic Icecap grew suddenly to its present size 16 MBP and caused a large sea level drop. Production of cold Antarctic water accelerated, resulting in full blown Antarctic Bottom Water.
Miocene fluctuated until it ended with a massive cooling at 6 MBP. Sea level dropped again presumably as more water became locked up in the Antarctic icecap. The Mediterranean became isolated and completely evaporated locking up significant amounts of salt. Lower ocean salinity resulted in higher freezing point, pushing sea ice further south.
World warmed briefly in Pliocene.
Icecaps finally began to appear in the northern hemisphere 3 MBP. Their development was indicated by an abrupt shift in oxygen isotope ratios and ice rafted cobbles in marine sediments. Northern glaciation is linked to closure of the Panamanian Isthmus. This pushed warm gulf stream further north and the increased warm water brought more moisture to high latitude facilitating ice cap development.
Ocean Circulations Model Mesozoic
time – from early to present
Oceans circulation: Cenozoic
In the course of the Cenozoic, the abyssal ocean temperature declined, usually slowly, but sudden major cooling occurred at the Eocene/Oligocene boundary and in the middle Miocene. In low latitudes, surface temperatures change little, but in the far south the Eocene saw a drastic drop from the Paleocene high of 15oC. Thereafter surface temperatures remained roughly constant. The temperature scale on the right holds true only until about 15 MY ago.
The shaded areas in Quarternary on the left reflect the rapid large-scale temperature fluctuations of the last two or three million years. The curves are based on oxygen isotope curves of planktic and benthic foraminifera.
- Greater contrast in temperature between equator and poles continued to develop.
- Colder oceans resulted in less global rainfall.East Africa became dried and changed from tropic to savanna.
ACTIVITY 5 Questions
- What is the difference in surface temperatures of the low and mid latitudes at the Crestaceous/Paleocene boundary?
- Describe the patterns of low and mid latitude surface temperatures. What are the maximums, minimums, trends?
- Describe the patterns of the mid latitude surface and abyssal temperatures. What are the maximums, minimums, trends?
- What predictions can you make about their temperatures?DIRECTION OF FLOW OF SURFACE OCEAN CURRENTS AND DRIFTING AND MELTING ICEBERGS
The stream of ice that drained the Hudson Bay portion of the Laurentide ice sheet of North America, as well as the extent of the Greenland and North America ice sheets, and the ice covering Great Britain, are also shown. Surges in the ice stream from the Laurentide ice sheet might have been responsible for Heinrich events. Heinrich events occurred when North Atlantic was coldest and great flows of melting icebergs resulted from sudden collapse of icecaps. These events accompanied rapid changes in climate.
When Icecaps advanced, a pool of meltwater covered the surface of the North Atlantic. Reduced salinity water blocked the northward flow of Gulf Stream. With thermohaline circulation shut down, cold conditions in the North Atlantic werereinforced.
When the Icecap retreated, a pool of meltwater eventually retreated from the North Atlantic. Thermohaline circulation started again, resulting in the resumed northward flow of Gulf Stream.
ACTIVITY 6 Questions
- Compare the location of the ice sheets between the last ice age and now.
- Compare the iceberg flow between the last ice age and now.
- Compare the surface temperatures of the North Atlantic between the last ice age and now.
- What happened to the surface temperature when the ice flow water hit the warm current during the last ice age?
- What happens to the surface temperature now when the ice flow water hits the warm current?
- (TOC 3.1.1.a)
MIDDLE CRETACEOUS OCEANS
In the Middle Cretaceous, tropical and subtropical vegetation and animals existed in the high latitudes. The area of land (shaded) was sharply reduced and shallow seas were widespread, especially at low latitude.
The arrow shows where dense, warm, saline water from shallow seas might have spilled into deep basins, thus forming warm rather than cold abyssal waters.
Mesozoic water temperatures
- had little latititudinal or vertical variation.
- water temperatures were relatively high:
25-30oC in the equatorial regions.
12-15oC at 60o to 70o N and S.
polar temperatures of 10-15oC.
abyssal temperatures at 2000 m was 15oC.
Present Day abyssal temperatures
1-4oC at 2000 m.
ACTIVITY 7 Questions
- Trace the ocean circulation in the map and decide the kind of seaway it is.
- Describe the location (relative and absolute) of the coal beds, tropical and subtropical evaporates (salts), and tropical animals in the Mesozoic.
- Where would you find these tropical evaporates and animals today? Explain why.
- Use the TimeScale to see what other significant events (land, vegetation, animal) were occurring.