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EARTH’S STRUCTURE & MOTION
Chapter 4.1: Earth’s Formation
Key Idea Earth formed from a whirling cloud of gas
and debris into a multilayered sphere, which has since been losing heat.
Geology
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)
Origin of the Solar System 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 Animation
Earth’s Size and Shape
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
Example of Scientific Evidence
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!!!
Quick Facts About Earth
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
Layers of the Earth
Science Burrito Lab Follow Up
Video Wrap Up
Earth’s Heat
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
Earth Has Been Slowly Losing Heat
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 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