The Earth: OUR Planet (Chapter 9 in your book)

The Earth is unique as a planet, because it has life on its surface, and also: - it is the largest of the terrestrial planet: its mass is larger than that of Mercury, Venus and Mars

combined together - It has liquid water on its surface distinctive blue color - It has active volcanoes, plate tectonics - It has a dynamic atmosphere in which the water, land and air are involved

I. The Interior of the Earth (9.2) - The density of rocks is about 3000kg/cubic meter: 3 times that of water a bucket full of rocks

is 3 times as heavy as a bucket full of water - The average density of Earth (its mass divided by its volume) is about 5500km/cubic meter: 5.5

times the density of water the inside of the Earth must have an even higher density than rocks. THE EARTH HAS THE HIGHEST AVERAGE DENSITY OF ALL THE PLANETS !!!!

The abundance of elements (atoms) in the Universe (in the Sun, stars, inter stellar medium, etc..) is as follows on a logarithmic scale (the vertical scale is a log scale, so a difference of 1 means 10 times larger, a difference of 2 is 100 times larger, 3 is 1000 times, and so on…)

The most abundant are

- H - Hydrogen and - He - Helium, which have both mostly escaped from Earth,

and the heavier elements that are abundant are - C - Carbon, - O - Oxygen , - N - Nitrogen, - Si - Silicon and - Fe - Iron. - Ni – Nickel - Ne - Neon also easily escapes as it is a gas.

So the candidates for the Earth interior could be C, N, O, Si, Fe,… Because of the magnetic field of the Earth, Fe (Iron) is the best candidate for the interior of Earth, it is also the heavier explaining the high density of the Earth.

Initially, when the Earth formed, it was very hot because of the multitude of impacts that created the Earth, and also because of the decay of radio-active elements. The Heavier elements (Iron, Nickel,..) sank to the center of the Earth and the Lighter elements “floated” to the surface Iron-rich Core and Silicon-rich Crust; The Mantle is made of Iron-rich minerals

The sinking of the heavier elements towards the center and the floating of the lighter elements to the surface is called “CHEMICAL DIFFERENTIATION” OR “GRAVITATIONAL SEDIMENTATION”. (more precisely the chemical differentiation is the fact that different elements separate from each others, and gravitational sedimentation is the physical process that actually leads to chemical differentiation) As the Earth cooled down it kept its layered structure. The Earth is 4.56 billion years old

EARTHQUAKES TO PROBE THE INTERIOR OF THE EARTH Earthquakes (at the surface of the earth) produce

- longitudinal waves (in the direction of motion) called P (primary) waves and - transverse waves (perpendicular to the direction of motion) called S (secondary) waves. - S waves do not travel through liquids - Both P and S waves changes direction of motion (they are REFRACTED) when passing form a

region that is liquid to a region that is solid and vice versa. - These P and S waves can be measured around the earth with seismographs. - From the transmission of these waves we learned that

The EARTH HAS - A SOLID INNER IRON CORE FROM 0 TO 1300KM (IT IS SOLID DUE TO HIGH PRESSURE) - A LIQUID OUTER IRON CORE FROM 1300KM TO 3500KM - A “PLASTIC” MANTLE MADE OF IRON-RICH MINERALS AND MAGNESIUM FROM 3500KM TO

6343 KM - A CRUST COMPOSED OF SOLID ROCKS FROM 6343 – 6378KM (5 TO 35KM THICK)

II. The Crust of the Earth (9.3) CONTINENTAL DRIFT : If you look at a map of the earth:

You can easily imagine the continent being pieces of a giant puzzle that fit back together: the PANGAEA

super continent

The continental drift began some 200 million years ago, at the time of the dinosaurs

PLATE TECTONICS: THE CRUST IS MADE OF PLATES FLOATING ON THE VERY UPPER LIQUID SURFACE OF

THE MANTLE

- The upwelling of new material from the mantle to the crust pushes the existing crusts apart

The flow of lava is a convective flow: the warmer material moves up (like a hot air balloon), after it cools it moves down. The Mid-Atlantic Ridge is a gigantic mountain ridge that rises from the floor of the North Atlantic Ocean, It is caused by an upward flow of lava This causes the sea floors to move side way (to separate) . The Crust is made of Plates that are moving due to Lava flow under them, the crust of the earth is

renewing itself. The Continents are drifting due to the motion of the plates on which they are located.

Volcanoes and Earthquakes happen mainly at the boundaries of the large plates the crust is made of,

there the plates collide, slide, or go one under the other (subduction) The earthquakes are due to

collision and friction between plates.

Volcanoes are due to lava flow pushing upward.

Some mountains are due to one plate going under another plate and pushing it up – a subduction zone.

Subduction examples: The Alps due to Italy, the Tibetan plateau due to India, etc… see Google Earth

EARTH’S PLATES: WHERE THE PLATES MEET IS WHERE EARTHQUAKES AND VOLCANIC ERUPTIONS

HAPPEN MOST OF THE TIME

- FOR EXAMPLE EARTHQUAKES IN CALIFORNIA, NORTH AFRICA, JAPAN, ETC…

III. The Surface of the Earth (9.1, 9.5, 9.6) - The atmosphere is made up of mainly Oxygen (1/5) and Nitrogen (4/5) - 71% of the earth surface is covered with water

- The water is in constant motion

- The Earth Atmosphere is also in constant motion/activity

- The Atmosphere and oceans are connected through rains and evaporation, winds, etc…

- The Sun is the main energy source to power the motion of the atmosphere and oceans

- Tidal forces also power the motion of oceans

The Atmosphere The Sun warms up Earth’s surface which heats up the warm surface heats up the air

CONVECTION : hot air rises and eventually cools down, as it cools it moves back down, creating a circular

motion call a convective cell: e.g. heating up water in a pot

FORMATION OF CLOUDS: the heat from the sun evaporates water to form clouds. The amount of water

in a thunderstorm cloud is 500,000,000kg (5 hundred thousand tons), the energy of the sun basically

“lifted” that much water in the sky. As the water condenses into rain and falls it releases that energy

back somewhere else.

Above a given height all the water has condensed into clouds, so above that given height there are no

clouds this is why clouds are not found at 30,000feet when you fly on a planet.

Currents of water in the sea are also due to heating from the sun warm water from the equator

moves close to the surface toward the poles; and the cold water from the poles moves close to the

bottom of the ocean floor toward the equator.

THE GREENHOUSE EFFECT ON EARTH

- Albedo of the Earth is 0.31, this is due mainly to clouds, snow, ice and sand reflecting sunlight.

- The Earth absorbs 69% of the sunlight it receives

- The Earth average temperature is constant, so it emits (loses) as much radiation (energy) as it

absorbs.

- The Earth temperature is 287Kelvin (57F) so it emits in the Infrared .

- If one calculates the temperature of the Earth using how much energy it receives from the Sun,

one obtains only 254K (-2F!) the oceans should be frozen…

THIS IS BECAUSE OF THE GREENHOUSE EFFECT

- Not all the infrared emitted by the Earth escapes to space, some of it is trapped in the

atmosphere

- Water vapor, CO2, Methane, help trap some of the infrared light and keep the earth close to

60F!

The Same happens on Earth:

DYNAMICS OF THE ATMOSPHERE

- The atmospheric pressure is the weight of the air above you pushing down on you, at sea level it

is 100,000Newton per square meter or 10 Newton per centimeter square (equivalent to 14.7

pounds per square inch). This 1 (one) atmospheric pressure (1 bar)

- As you go to a higher altitude, there is less air above your head and the atmospheric pressure

decreases.

- The Temperature in the atmosphere changes with altitude

- Troposphere: the temperature increases closer to the surface due to heating from the ground

by Sun Light.

- Stratosphere: the temperature increases with altitude as sun ultraviolet (UV) radiation is

absorbed by Ozone (O3) ;

- In the Mesosphere there is much less ozone and so the temperature again decreases with

altitude

- In the thermosphere oxygen (O) and nitrogen (N) are not found in the form of molecules (e.g.

O2) but as individual atoms. These atoms are accelerated due to solar radiation and that

increases the temperature of the gas (the temperature of a gas is a measure of the quantity of

motion of the particles the gas is made of).

ROTATION OF THE EARTH AND DEFLECTION OF WINDS AND CURRENTS

Due to the (westeast) rotation of the Earth,

- winds moving away from the equator are deflected East as they originate from a region of

higher rotational velocity

- winds moving to the equator are deflected to the West as they originate from a region of lower

rotational velocity

With the convection currents in the atmosphere and the deflection, the atmospheric circulation

patterns take the following patterns:

There are 3 “convective cells” on each hemisphere. The Surface winds are as follows:

FORMATION OF HURRICANES (CYCLONES AND TYPHOONS)