Ch 9 SummaryI have learnt that earth is called blue planet because it contains 71% ocean water. 360 million square kilometers out of 510 million square kilometers is covered by water. Oceans and continents are different in Northern and Southern Hemisphere. Northern Hemisphere have 61% water and 39% land while Southern Hemisphere have 81% water and 19% land. There are four main ocean basins. Pacific Ocean covers half of ocean surface, Atlantic Ocean covers half the size of the Pacific Ocean, Indian Ocean smaller than the Atlantic Ocean and Arctic Ocean is 7% of the size of Pacific Ocean. Sea water contains 3.5% salt and is not suitable for drinking. The source of dissolved minerals or salts is the weathering of rocks. Various processes changes the proportion of water in sea and thus changes salinity. For example fresh water enters into sea reduces salinity. Atlantic Ocean is saltiest ocean. Water from Amazon River reduces the salinity of Atlantic Ocean. Basic ocean-water properties that influence deep-ocean circulation, distribution and types of life-forms. If thermometer is entered into the ocean then we will see thatsurface temperature will be more due to sun light while at depth temperature will be less. Densityeffects water’s vertical position and salinity is effected by salinity and temperature. Increase in salinity increases density while increase in temperature decreases density. There exists low-density water found near the surface while higher-density water is found below.Different features like volcanic peaks, deep trenches, extensive plains, mountain chains will be visible if water is removed from sea. Bathymetry is the technique of measuring ocean depth and echo sounders was the first device to measure water depth. It has discovered that ocean surface isnot flat because stronger-than-average gravitational attraction is exerted by massive seafloor features which produces elevated areas. Oceanographers have divided topography of sea into three parts, continental margins, the deep-ocean basins, and the oceanic (mid-ocean) ridges. I have studied that there are two types of continental margins passive and active margins. Indian Ocean is passive continental margins while Pacific Ocean is active continental margins. There are different features of passive continental margins like continental shelf, the continental slope and continental rise. Deep ocean basin lies between oceanic ridge and continental margin. Deep ocean basin include Deep-ocean trenches which is long, narrow and deepest part of ocean, Abyssal plains which is deep and flat. There are many volcanic structures present in ocean floor like Seamounts and Volcanic Islands, guyots and oceanic plateaus. Mid-ocean ridge is formed when seafloor is elevated. I have learnt that East Pacific Rise is not the feature of “mid-ocean”. There occur some feature in mid-ocean ridge like rift valley.I have studied that seafloor contains sediments. There are several types of seafloor sediments liketerrigenous sediment which contains mineral grains, biogenous sediment which contain shells and skeletons of marine animals and hydrogenous sediment which contain minerals that have crystallize from seawater. We have learned that earth processes change when any of the process in earth changes. When any animal die then their remains settled to ocean floor and they become a part of sedimentary record. In this way scientists learn about environmental changes in ocean.I have learned that earth contains 71% water. Ocean contains sediments that are useful for the learning the environmental conditions that changes with time because most of the sediments arevery old that are preserved in oceans. If we could get those fossils or sediments then we can learnabout previous environment of ocean.I have a question for you that what are the other ways to learn ocean