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