Chapter 2.1 Earth: a Unique Planet

Three Reasons the Earth is Unique … It is the only known planet with liquid surface water. It is the only known planet with an oxygen atmosphere. It is the only known planet to support life.

Three Facts About the Earth … The Earth is the third planet from the Sun. The Earth is 4.6 billion years old. 71% of the Earth's surface is covered by ocean.

The Earth: an Oblate Spheroid The Earth is not completely round; therefore, we can’t refer to it as a perfect sphere. The true shape of the Earth is an oblate spheroid, meaning a slightly flattened sphere (In other words, the Earth is slightly squished.). The spinning of the Earth on its axis causes it to flatten slightly at the poles and bulge in the middle.

The Circumference of the Earth The Earth’s circumference is 40,007 km from pole to pole and 40, 074 km around the Equator. Pole Equator

From the Tallest Mountain to the Deepest Trench The difference in height from the tallest mountain to the deepest trench on Earth is only 20 km.

The Size of the Earth The average diameter of the Earth is 12,756 km.

How do we know about the Earth ’ s interior? The Earth ’ s interior is is studied with seismic waves called P (primary) and S (secondary) waves. P and S waves travel faster through more rigid, dense materials and slower through more plastic, less dense materials. Both types of waves are deflected when they enter a medium of different density. S waves do not travel through liquids, such as the Earth’s outer core and therefore can’t be detected past 103  from an earthquake’s epicenter. P waves are deflected by the liquid in the Earth’s outer core and can’t be detected between 103  to 143  from an earthquake’s epicenter.

The Three Compositional Zones of the Earth The Earth is divided into three major compositional zones: the crust, the mantle, and the core. ALL parts of the Earth are solid except the outer core which is liquid. The crust and the mantle are composed of rock. The core is composed of denser metals. The crust makes up less than 1% of the Earth’s mass, the mantle 2/3 of its mass, and the core 1/3 of its mass. The crust is by far the thinnest layer (It is less than 100 km thick; The mantle and core are 1000s of km thick.).

Earth ’ s Crust … Its Not All Created Equally!!! Oceanic Crust – the Earth ’ s crust under the oceans that makes up the ocean basins (ranges from 5 to 10 km thick). Continental Crust – the Earth ’ s crust that makes up the continental landmasses (ranges from 15 to 80 km thick). Ocean crust is made of a more dense material than continental crust.

The Five Structural Zones of the Earth The Earth's five major structural zones: the lithosphere, the asthenosphere, the mesosphere, the outer core, and the inner core. The thickness of the five zones are as follows: 1.lithosphere km thick. 2.asthenosphere km thick. 3.mesosphere - ends at a depth of 2900 km. 4.outer core - begins at a depth of 2900 km and goes down to 5150 km thick. 5.inner core - begins at 5150 km thick and goes to the center of the Earth (6,378 km).

The Lithosphere and the Asthenosphere Lithosphere – the Earth ’ s crust (both oceanic and continental) combined with the rigid, brittle upper mantle that forms the outer shell of the Earth. Asthenosphere – part of the “plastic” (i.e. It flows.), lower mantle directly underneath the lithosphere. The asthenosphere is plastic because of the pressure on it from the lithosphere above. The less dense, lithospheric plates, including the oceanic and continental crust, “ float ” on the more dense, “ plastic ” asthenosphere directly below.

The Earth ’ s Magnetosphere The Earth’s magnetosphere is the name given to the Earth’s magnetic field.This field extends from the magnetic North Pole to magnetic South Pole and out into space. It’s currently believed that the movement of molten iron in the Earth’s outer core causes the production of electric currents which in turn produce the Earth’s magnetic field.

Mass vs. Weight Newton’s Law of Gravitation states that the force of attraction (gravity) between two objects depends on their masses and the distance between them. The more massive they are and the closer they are together, the greater the attraction. Mass is the amount of matter that makes up an object. Weight is the effect of gravity on that mass. The father you are from the center of the Earth, the less your weight. Therefore, your weight decreases as you travel from a pole to the equator, up a mountain, or off the surface of the Earth (ex. On the surface of the Earth, a 1 kg mass = a 10 N weight/At 13,400 km above the Earth’s surface, a 1 km mass = a 1 N weight.). weight decreases mass is constant weight increases mass is constant