6 A giant magnet Geographic North Pole You can think of the Earth as having a gigantic bar magnet buried inside The Earth’s magnetic field pulls objects towards it in the same way as the bar magnet Although we don’t feel it the Earth is spinning around an imaginary line At the top is the North Pole and at the bottom is the South Pole These are the geographic poles The poles are slightly off center because the Earth is tilted at a slight angle N S Winter at the North Pole is extremely cold and ice-locked Magnetic North Pole N S The magnetic field of a bar magnet can be seen if iron filings are placed around it They show the shape of the field It’s strongest at the north and south poles Magnetic pOles Because the outer core of the Earth is fluid iron itTs able to move or flow This movement creates an electric current which in turn creates a magnetic field The imaginary magnet doesnTt run exactly along the EarthTs rotational axis ItTs skewed slightly off center So the magnetic north pole is close to the geographic North Pole and the south magnetic pole to the geographic South Pole
Magnetic field The Earth produces its own magnetic field This is fairly weak on the surface After all the planet Earth is almost 8077,8 miles in diameter so the magnetic field has to travel a long way to affect your compass ThatTs why a compass needs to have a lightweight magnetic needle that spins easily Without this there just isnTt enough strength in the EarthTs magnetic field to turn the needle Gravity Gravity is one of the natural forces ItTs the force that causes matter such as rocks to attract one another ItTs gravity that holds the planets in our solar system in place around our Sun ItTs also gravity that holds the stars in our galaxy in place The strength of the gravitational force depends on the mass of an object You would think that gravity must be a very strong force but in fact itTs quite weak Every time you lift up an object you are overcoming the EarthTs force of gravity 7 A compass needle always points north Metal at the center No one knows for sure but the EarthTs outer core is thought to consist largely of molten iron At the very center of the Earth the pressure is so great that this huge collection of super-hot iron crystallizes into a solid The heat that is It is gravity that holds the planets in our solar system in place around our Sun given off from the inner core spreads in a circular movement following the rotation of the Earth It causes the liquid iron in the outer core to move in a rotational pattern too ItTs thought that these rotating forces in the liquid iron layer create the magnetic forces around EarthTs axis
8 Different rOcks You can find rocks all over the Earth but they’re not all formed from the same kind of material And they may have been made in different ways But over millions of years they have all been pressed into shapes smashed or ground down or even heated so much they melt Sedimentary rOck Sedimentary rock is a kind of rock that is formed from stones mud and in some cases parts of tiny plants and animals This is known as sediment Sediment forms on riverbeds sea beds and lake bottoms Over thousands of years as more sediment is laid down the layers below are squeezed to form hard rock Sandstone and limestone are sedimentary rocks Chalk is a sedimentary rock thatTs made up of the shells of tiny animals Strata yOu can see When sedimentary rocks form they usually do so in layers called strata A stratum can be just less than one inch thick or as much as several inches thick At first strata are laid down horizontally but shifts in the EarthTs crust can make them look like waves or even move them into an upright position Examining strata helps scientists to date the rocks Layers of different rock form over millions of years chalk limestone sandstone mudstone
Cenozoic Mesozoic Palaeozoic Pre-Cambrian Uluru the famous rock in northern Australia is made of sandstone 9 ROck time Throughout the history of our planet layers of rock have formed one on top of the other This has led to scientists using the layers as time markers Each rock layer is dated by the period in which it was formed This method of dating is called geological time Geological time goes back billions of years ItTs divided into four huge chunks called eras Precambrian Palaeozoic the Greek for old life Mesozoic middle life and Cenozoic recent life The eras are divided into shorter time chunks called periods Dinosaurs lived during the Jurassic period of the Mesozoic era We live in the Holocene period of the Cenozoic era KEY WORDS sedimentary rock sandstone limestone strata geological time era period Chalk cliffs line the coast of parts of southern England
