hello students welcome to grade 10 science lessons and i'm your teacher marian viseriano in today's lesson we will discuss about the distribution of earthquakes volcanoes and mountain ranges you have learned from your past science lessons that philippines is part of the pacific ring of fire this means that our country and other places located at the ring of fire experience earthquakes volcanic eruptions and other tectonic activities how are volcanoes mountains and other geologic features formed let's study first the earth's lithospheric part earth's lithosphere consists of layers the cross and the upper part of the mantle the cross is made of a variety of solid rocks like sedimentary metamorphic and igneous it has an average density of 2.8 gram per cubic centimeter and its thickness ranges from 5 to 50 kilometers there are two kinds of crust oceanic crust and continental crust can you tell the differences between the two crusts [Music] here are the differences and similarities between the oceanic crust and continental crust for the oceanic crust it is more dense made of mostly basil thickness five to ten kilometers or three to six miles and mostly younger and newer rocks while continental crust is less dense made of mostly granite rocks thickness 30 to 50 kilometers or 20 to 30 miles and it consists mostly of all the rocks for the similarities of the two crusts they are both made of rocks they are solid make up tectonic plates and part of the lithosphere according to the plate tectonics model the entire lithosphere of the earth is broken into numerous segments called plates what makes this map different from other maps what do these broad lines represent the map shows that the outer shell or layer of earth the lithosphere is broken up into tectonic plates that are gradually moving the broad lines represent the plate boundaries what do you think are the basis of our scientists in marking the plate boundaries let's examine the following maps figure one shows the distribution of major earthquakes or epicenters figure 2 shows the distribution of major active volcanoes figure 3 shows the distribution of major mounted belts of the world and figure 4 shows the major plate tectonics now let's put all together the maps do you notice anything can you tell now the basis of our scientists in marking the blade boundaries the places of earth where most of the earthquakes originated or some mountains and volcanoes were formed mark the boundaries of each lithospheric plate to summarize what you have learned in today's lesson plates are large pieces of the upper few hundred kilometers of earth that move as a single unit as it floats above the mantle the plates are in constant motion as they interact along their margins important geological processes takes place such as the formation of mounting belts earthquakes and volcanoes i hope you enjoyed and learned something today this is my marian sriano see you in our next lesson [Music] you