Chapter 4.1: Earth’s Formation

 Earth formed from a whirling cloud of gas and debris into a multilayered sphere, which has since been losing heat.

 The study of the planet Earth:  It’s structure  Composition  How it has changed over time  The Earth as we know it is the result of changes that have occurred over billions of years (It didn’t get like this over night)

 Nebular Hypothesis (most widely accepted)  About 4.6 billion years ago….  A large cloud of gas and dust began rotating slowly in space  As time passed, the cloud shrank under the pull of its own gravity. The rate of rotation increased as it shrank  Most of the material in the cloud gathered around the center  The compression of the material made its interior so hot  hydrogen fusion occurred  Result: the sun and planetismals were born  Over time: nearly all of the material from the original cloud became orbiting planets as well  See: Origin of Solar System AnimationOrigin of Solar System Animation

 Earth is not a perfect sphere – oblate spheroid  Sphere that bulges in the center  Cause: the spinning motion of the Earth  How do scientists know this?  They can measure the weight (in Newtons) of an object at several places on the Earth’s surface  Recall: the weight of an object, in Newtons, is the force with which gravity pulls an object toward the center of the Earth  The further an object is from the center, the lighter it is, and the closer, the heavier it is

 An object at the North or South Poles weighs 195 Newtons  At the equator, that same object weight 194 Newtons  What does this evidence tell you?  An object is closer to the Earth’s center at the poles than the equator  If Earth were a perfect sphere  an object would be the same distance from the center at ALL points and so would the object’s weight!!!

 29% land or 149 million square miles  71% water or 361 million square miles  Earth’s original surface was very similar to the surface of the moon  Earth was most likely composed of the same material from the surface all the way to the center

 Video Wrap Up Video Wrap Up

 Events that formed Earth produced heat  Heat came from:  Meteorite impacts  Weight of overlying materials caused compression in Earth’s interior  Decay of radioactive isotopes

 Reasons:  Some rocks lose heat more quickly than others  The thickness of the crustal rock varies from place to place  The percentage of radioactive materials in rocks varies

 Earth’s Magnetic Field  Imagine a bar magnetic inside the Earth tilted 11 degrees away from the poles  The field is the resulting lines of force that loop from one end of the bar magnet to the other  11 degree tilt explains why the magnetic north pole and geographic north pole are not in exactly the same place  North end = attracting = positive end  South end = repelling = negative end