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(6) Earth in space and time. The student knows the evidence for how Earth's atmospheres, hydrosphere, and geosphere formed and changed through time. The student is expected to: (c) investigate how the formation of atmospheric oxygen and the ozone layer impacted the formation of the geosphere and biosphere Diatomic Oxygen Oxygen reacts with the iron in the geosphere creating iron oxide (rust) Levels of atmospheric diatomic oxygen and dissolved diatomic oxygen influenced aerobic life. Stratospheric ozone protects terrestrial life from UV radiation allowing life to flourish (d) and evaluate the evidence that Earth's cooling led to tectonic activity, resulting in continents and ocean basins The geosphere refers to everything from the core of the Earth to its surface. As you can see, there are many features within the Earth that we will learn about. The biosphere is the layer of life on Earth. It exists beneath, upon, and above the surface in the atmosphere as well. Axolotl Soil Nematodes Airborne Bacteria Harvestman 1. What are some of the Earth’s features within the geosphere? 2. What is the biosphere? One thing most geologists agree on is that the Earth’s first atmosphere contained no free oxygen. There were trace amounts of Oxygen bound in water molecules, and Carbon dioxide…but none of it was “free”, or molecular oxygen. (O2) Photochemical Dissociation Hypothesis states that the sun’s energy helped the atmosphere evolve through the following processes: The ultraviolet light combined with the water vapor to set the hydrogen off into space and free the oxygen. 2H2O + UV light energy ----> 2H2 (freed into space) + O2 The newly freed oxygen reacted with methane, forming carbon dioxide and additional water vapor. CH4 + 2O2 ----> CO2 + 2H2O The oxygen also reacted with ammonia, producing nitrogen and water. 4NH3 + 3O2 ----> 2N2 + 6H2O After converting the ammonia and methane to carbon dioxide and nitrogen, free oxygen began to accumulate as further dissociation of water vapor continued. 3. What is meant by “free oxygen”? 4. Besides water, what other molecules play a huge role in photochemical dissociation? 5. What happens when freed oxygen combines with methane? 6. What happens when freed oxygen combines with ammonia? This theory states that our atmosphere was delivered to us from the Earth’s interior through volcanic eruptions. In contrast to the Photochemical Dissociation Hypothesis, the Outgassing Hypothesis argues that the free oxygen came from the photosynthesis of primitive organisms which existed 1.5 - 3.5 billion years ago. The oxygen took approximately 2 billion years to become free, but when it did, it formed the ozone layer, eliminating the dangerous radiation and setting up the foundation for a habitable planet. It is obvious that Earth contains O2 now, and without it, aerobic life would not be possible. What life could have evolved all those billions of years ago, before there was significant O2 in our atmosphere? Anaerobic life forms http://www.teachersdomain. org/resource/tdc02.sci.life.ce ll.stetteroxygen/ Although the early Earth was mostly devoid of molecular oxygen, high volcanic activity released significant amounts of molecular hydrogen. With little oxygen available to convert that hydrogen into water, hydrogen gas probably accumulated in the atmosphere and oceans in concentrations as high as hundreds to thousands of parts per million. Thus, the early Earth was likely a paradise for methanogens (methane-producing bacteria) that fed directly on hydrogen and carbon dioxide, at least until the atmospheric hydrogen was depleted. 7. What primitive organism uses photosynthesis to combine CO2 and water in the presence of sunlight to make sugar and O2? 8. What are methanogens, and why was early Earth a paradise for them? 9. Where did these methanogens retreat to, when oxygen started evolving in our atmosphere? 10. Where did the molecular hydrogen of the Earth’s first atmosphere likely go? Many anaerobic microbes including methanogens are easily poisoned by oxygen, and the recent discovery of banded sediments with rusted iron suggests that oxygen-producing, photosynthetic microbes called cyanobacteria were able to gather sunlight for photosynthesis. These BIFs would not have formed without O2 present in the atmosphere. The evolution of O2 in our atmosphere spelled doom for the proliferate methanogens, and other types of extremophiles that had evolved during this early period in Earth’s past. Despite their small stature, one of the first aerobic organisms (require the presence of O2) set in motion a process that would change everything. These cyanobacteria which evolved 3.5-1.5 billion years ago (also known as blue-green algae), were remarkably self-sufficient creatures that could use the sun’s energy to make their own food, and fix nitrogen, a process where nitrogen gas is converted into ammonia or nitrate. (NH3; NO3) While this may not seem significant, the cycling of nitrogen on Earth is essential for life. It is found in amino acids, proteins, and genetic material. Nitrogen is the most abundant element in the atmosphere (~78%). However, gaseous nitrogen must be 'fixed' into another form so that it can be used by living organisms. 10. How do are banded iron formations created…and why can’t they form anymore? 11. What does it mean to “fix” nitrogen? 12. Why is the cycling of nitrogen so important to life on Earth? And then...nothing else happened. At least, not for another two billion years! It wouldn't be until about 600 million years ago, that the first multicellular organisms finally emerged. So what happened during that immense, multi-billion year gap? Why did it take so long for more complex life to arrive on the scene? For that matter, why did oxygen suddenly spike 2.5 billion years ago? The simple, uncomfortable answer is that we don't really know. ??? We already know that over time, the Earth’s crust cooled. The crust is thin, relatively, varying from a few tens of kilometers thick beneath the continents to less than 10 km thick beneath the oceans. The crust and upper mantle together constitute the lithosphere, which is typically 50-100 km thick and is broken into large plates. These plates sit on the asthenosphere. The asthenosphere is kept plastic largely through heat generated by radioactive decay. This heat source is relatively small, but nevertheless, because of the insulating properties of the Earth's rocks at the surface, this is sufficient to keep the asthenosphere plastic in consistency. 13. Why was there a huge 2 billion year gap between the first origins of life and oxygen in the atmosphere, and the appearance of more complex life forms? 14. What is the lithosphere composed of, and what does it sit on top of? 15. What keeps the asthenosphere plastic? Energy can be transferred in three ways… com/watch?v=p0d of space Radiation Energy transfer across the vacuum WF_3PYh4 Conduction Energy transfer directly from molecule to molecule (solids) Convection Energy transfer through fluids (liquids and gases) http://www.youtube. Very slow convection currents flow in the asthenosphere, (upper portion of the mantle) and these currents provide horizontal forces on the plates of the lithosphere much as convection in a pan of boiling water causes a piece of cork on the surface of the water to be pushed sideways 16. Give an example of how Earth experiences the transferal of thermal energy in the form of radiation. 17. Give an example of conduction of thermal energy. 18.Give an example of convection of thermal energy. 19. In what media does each type of thermal energy transfer? Of course, the timescale for convection in the pan is seconds and for plate tectonics is 10-100 million years, but the principles are similar. Differentiation within the Earth is crucial to plate tectonics, because it is responsible for producing an interior that can support tectonic motion. The heat generated by the lower mantle, drives the convection currents upward against the lithospheric plates. As the currents cool, they move laterally, pushing and pulling the lithosphere apart. Then, the currents move downward again, where they begin to heat up once more due to proximity to lower mantle heat. While seemingly static, the geosphere is in fact a very active player in the Earth systems, affecting the atmosphere and the hydrosphere, as well as critical processes such as the hydrologic cycle and other biogeochemical cycles. The types of minerals contained in soils--a factor of geologic processes--help to determine the vegetative cover and ecosystems at the surface. Carbon – an essential element of life – is bound in organic matter and is carried to the ocean via wind and water erosion where eventually it becomes part of the ocean floor. 20. How does the geosphere influence the biosphere? 21. How does the geosphere influence the hydrosphere? 22. Why has the differentiation of the Earth been so important a factor in tectonic movement? Tectonic movement carries the ocean deposits into the Earth's interior. On geologic timescales, volcanic activity can vent the carbon to the Earth's atmosphere as carbon dioxide. The carbon cycle is one of the key cycles linking the Earth’s subsystems: geosphere, atmosphere, hydrosphere, and biosphere. The outer core of the Earth contains liquid iron. Its motion is thought to drive the Earth's magnetic field – the magnetosphere - which extends far beyond the atmosphere protecting Earth and its biosphere from solar wind and cosmic radiation. Being dynamic, the Earth is still changing. 150 million years in the future, the continents should look something like this. In 250 million years, we will have another pangea supercontinent.