Geo 2EQ: How do we describe Earth’s

position, and how do processes shape

the earth

How do we know anything about

the Earth

• Interior structure

• Volcanoes and hotspots

• Earthquakes

• Tectonic plates

• Tectonic motion

• Reconstruction of the Earth’s history

Interior

Based on Composition

• Crust – solid, relatively low density silicate rock

• Mantle – Semi fluid, denser (iron and magnesium bearing) rocks

• Core – Liquid then solid iron and nickel with traces of heavier elements

Based on Motion

• It turns out that the upper section of the mantle is adhered (stuck to the underside side of the crust to form what we call tectonic plates

Volcanoes

Volcanoes• Volcanoes are the result of hot spots within the

crust or mantle of the earth.

• The hot, liquid rock will break through weak

spots in the surface and form volcanoes or flood

basalts.

• Many volcanoes do not release lava, instead

they spit ash and small bits of lava called lapilli.

• Some eruptions are quiet with very fluid (low

viscosity) lava flows while others are explosive

Volcanoes

Quiet

lava

flows

Volcanoes

Mt. St. Helens before the explosive eruption

VolcanoesTime lapse of the eruption

Volcanoes

Mt. St. Helens after the eruption

Volcano locations

Earthquakes

Earthquakes

• Earthquakes are a result of motion within

the earth.

• This only occurs where the earth is solid

and therefore can only occur within about

100 miles of the surface

• Earthquakes provide the best evidence

regarding the interior structure of the

Earth.

Earthquakes

Earthquakes

Earthquakes

Earthquakes

Tidal waves or Tsunamis result when a large section of the sea floor

suddenly moves and therefore displaces a massive amount of water.

Earthquakes

Earthquakes by depth.

Notice that the deep earthquakes occur only at subduction zones.

Tectonic Plates

Types of Plate Tectonics

Subduction: a heavier sea plate dives

beneath a lighter continental plate.

Accretion: pieces of the Earth’s crust come

together slowly as the sea plate slides

under the continental plate.

Spreading: sea plates pulling apart

Types of Plate TectonicsSubduction: Causes violent earthquakes

and volcanic eruptions to form new land.

Accretion: less violent pushes land up

under ocean near shore line expand land

outward.

Spreading: Creates underwater volcanic

eruptions that create new land between sea

plates.

Subduction

Accretion

Spreading Plates

Spreading

Faults - cracks in the Earth’s crust

San Andreas

Fault

Tectonic Plates

Our first evidence of tectonic motion is based on similar fossils and

rock types on opposing sides of the ocean

Tectonic Plates

Pacific Ring of Fire

Most volcanoes and earthquakes on Earth.

Pangea• What is Pangaea?

• Pangaea was a super continent at one time.

• Scientists use the similarity of rock types and fossil types that date

to the same age to support their theory that the continents were

connected to form a super continent.

• The map below give just one example of areas on different

continents that show the same fossils and rock types.

Pangea

Pangea

The break up

of Pangea

Where are we going?

We appear to be headed for another

super continent as North America,

South America, Asia and Australia converge in the

ever shrinking Pacific Ocean

The Hydrosphere• About 70% of the earth’s surface!

• Factor for settlement.

The Water Cycle

• Run and get a glass of water and put it on the table next to you. Take a good long look at the water. Now -- can you guess how old it is?

• The water in your glass may have fallen from the sky as rain just last week, but the water itself has been around pretty much as long as the earth has!

The Water Cycle

Evaporation• The water cycle has no starting point. But,

we'll begin in the oceans, since that is

where most of Earth's water exists. The

sun, which drives the water cycle, heats

water in the oceans. Some of it evaporates

as vapor into the air.

Transpiration

• Water transpired from plants and

evaporated from the soil.

Do plants sweat?

Condensation• Water vapor in the air gets cold and changes back into

liquid, forming clouds. This is called condensation.

• Air currents move clouds around the globe

• You can see the same sort of thing at home... pour a glass of cold water on a hot day and watch what happens. Water forms on the outside of the glass. That water didn't somehow leak through the glass! It actually came from the air. Water vapor in the warm air, turns back into liquid when it touches the cold glass.

Precipitation

• Precipitation occurs when so much water

has condensed that the air cannot hold it

anymore. The clouds get heavy and water

falls back to the earth in the form of rain,

hail, sleet or snow.

Collection• When water falls back to earth as precipitation, it may fall

back in the oceans, lakes or rivers or it may end up on

land. When it ends up on land, it will either soak into the

earth and become part of the “ground water” (infiltration).

Some water infiltrates deep into the ground and

replenishes aquifers (saturated subsurface rock), which

store huge amounts of freshwater for long periods of time.

Some infiltration stays close to the land surface and can

seep back into surface-water bodies and some ground

water finds openings in the land surface and emerges as

freshwater springs. Over time, though, all of this water

keeps moving, some to reenter the ocean, where the

water cycle "ends" ... oops - I mean, where it "begins."

Bodies of Salt Water

• Oceans About 97 percent of the hydrosphere is a

huge body of salt water divided into five oceans:

the Atlantic, the Pacific, the Indian, Southern

and the Arctic Oceans.

• Seas, Gulfs, and Bays Large bodies of salt water

partially enclosed by land comprise seas, gulfs,

and baysHow can we use this water?

Desalination: converts ocean water into drinking water

Why aren’t we all doing this?

Climate vs. Weather

Climate is often confused with weather…

Weather is the condition of the atmosphere

in one place during a limited period of time

Climate is the term for the weather patterns

that an area typically experiences over a

long period of time.

Climate vs. Weather con’t…

• Example of WEATHER :

When you look out the window or

watch the news to see if you need an

umbrella today.

• Example of CLIMATE:

People who live in Seattle frequently

use umbrellas because of the rainy,

wet climate.

Climate vs. Weather con’t…

The climate & weather in a

particular region is determined by

many factors…the most important

of which is the earth’s position in

relation to the sun.

Earth’s Tilt & Rotation

The Earth’s tilt is one reason for variations in

sunlight. It is tilted at an angle, 23 ½

degrees, on an imaginary pole that runs

from the North Pole to the South Pole.

Tilt & Rotation Con’t…

• Because of the tilt of this axis, not all

places on the planet receive the same

amount of direct sunlight at the same time.

• For this reason, the angle of tilt affects the

TEMPERATURE…areas that receive a

large amount of direct sunlight have

warmer temps than places that receive

little sunlight.

ROTATION

The Earth rotates on it axis, making 1

complete rotation every 24 hours.

It rotates from WEST to EAST.

This is how we get day & night!

REVOLUTION

• While the planet is rotating on its axis, it is also

REVOLVING around the sun.

• It takes about 365 days to complete one trip

around the sun.

• The Earth revolves counterclockwise around the

sun.

• “About” refers to leap year, Feb. 29th, every four

years, as a result of 365 ¼ days.

Seasons

• The earth’s tilt & it’s revolution cause

changes in the angle and amount of

sunlight that reach different locations on

the planet.

• This results in the seasons.

SEASONS

• Fall – September 22

• Winter – December 22

• Spring – March 21

• Summer – June 21

SOLSTICE

• At 2 moments during the year the earth’s

poles point toward or away from the sun

more than at any other time.

• Definition: The time that the earth’s

poles point at their greatest angle toward

or away from the sun is called a solstice.

SOLSTICE con’t…

• Solstices occur around Dec. 21 & June 21.

• In the N. hemisphere, the day in Dec. on which the solstice occurs is the shortest day of the year and is the first day of winter.

• The day in June on which the solstice occurs is the longest day of the year and is the first day of summer.

EQUINOX

• Definition: An equinox, which means

equal night in Latin, occurs twice a year

when the earth’s poles are not pointed

toward or away from the sun.

EQUINOX con’t

• Both hemispheres receive an equal amount of

sunlight-exactly 12 hours.

• If you were to travel anywhere in the world

during an equinox, daylight and darkness would

last the same amount of time.

• Equinoxes occur around March 21 & Sept. 22

• The March equinox signals the beginning of

Spring & theSept. one signals the beginning of

fall.

POLES

• The amount of sunlight at the Poles varies

most dramatically as the earth’s revolution

and tilt cause the changing seasons.

• For 6 months of the year, one Pole is tilted

toward the sun and receives continuous

sunlight, while the other Pole it tilted away

from the sun and receives little to no

sunlight.

POLES con’t…

• At the North pole, the sun never sets from

about March 20-Sept. 23.

• It Is vice versa for the south pole.

• It switches 6 months later for each

location!

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