S2 Earth Forces Revision Help Sheet Below is a list of questions you should be able to answer before your test… How many layers are there in the Earths structure? There are 3 main layers to the Earth including the crust which is the outer shell, the mantle which is the largest section and the core which is the hottest and divided into the inner core and the outer core. What are plate boundaries? These are where the Earth’s crustal plates meet. They are the edges of the plates. Why are volcanoes and earthquakes found at plate boundaries? Plate boundaries are areas of thinner crust. They are the gaps between the plates. Plates are much weaker here. Why are volcanoes and earthquakes found around the Pacific Ocean? There are lots of plates colliding and separating around the Pacific Ocean. The plates are always moving there are lots of boundary lines. There is also lots of fault lines around the ocean. These movements can cause earthquakes and eruptions to happen. What moves the Earths plates? The Earth’s plates are moved by the convection currents in the mantle. These currents move the plates which float on top of them in the direction that they flow. What is Continental Drift? 260 million years ago all of the 7 continents were joined together in a Super continent called Pangea. Over millions and millions of years convection currents in the mantle have pushed and pulled the continents apart by moving the plates that they sit on. What instrument measures earthquakes? Earthquakes are measured by seismometers. The information collected is displayed on a seismograph. What is the scale used to record earthquakes called? The Richter scale or the Mercalli scale shows how powerful an earthquake is.