4th Nine Weeks
8 Grade SCIENCE EXAM STUDY GUIDE
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________________________________________Rocks__________________________________________
Classification of Rocks:
1.
Rocks are mixtures of minerals, volcanic glass, or other materials.
2.
When studying rocks geologists observe a rock’s color and texture and determine its mineral composition.
a.
Texture is the look and feel of a rock’s surface
1.)
If the grains are easy to see it is identified as coarse-grained
2.)
If the grains are too small to see if is identified as fine-grained
b.
Mineral composition – scientists study this by taking a small sliver of rock and looking at it under a microscope to
identify the crystal structure
Igneous Rock Notes
How Igneous Rocks Form:
1.
Igneous rocks form from the cooling of molten rock (either magma or lava)
a.
The name igneous comes from the Latin word ignis, meaning “fire”.
b.
Magma is molten rock that is below the surface
c.
Lava is molten rock that reaches the surface
How Igneous rocks are classified:
2.
Igneous rocks are classified according to their origin, texture, and mineral composition.
3.
Origin
a.
Intrusive Igneous Rocks – form from magma that hardens below the surface
b.
Extrusive Igneous Rocks – form from lava that has erupted to Earth’s surface
4.
Texture
a.
Intrusive Igneous Rocks – form large crystals and are coarse grained because the magma cools slowly
b.
Extrusive Igneous Rocks – form small crystals, are fine grained, even glassy; because the lava cools quickly
c.
Porphyritic – Intrusive rocks that have large crystals scattered on a background of smaller crystals. This shows the
magma cooled in two stages. First slow then rapidly.
d.
Volcanic Glass – rocks that cool so quickly that few crystals form
5.
Mineral Composition
a.
Basaltic igneous rocks are dark colored and dense
1.)
contain iron and magnesium but very little silica
2.)
basaltic lava flows freely from a volcano
b.
Granitic igneous rocks are lower in density and lighter in color
1.)
contain more silica and less iron and magnesium
2.)
granitic magma is thick and stiff
c.
Andesitic rocks have a more balanced composition of minerals and density than basaltic or granitic rocks
Sedimentary Rock Notes
Form from particles deposited by water and wind. They often form as layers.
How Sedimentary Rocks Form:
1.
Sediments are eroded and moved by wind, water, ice, or gravity.
2.
Then they are deposited – settled out of the water, wind, or ice carrying it.
3.
Compaction – occurs over time. The layers can become very thick. The thicker the layers the more they press down.
4.
Cementation – occurs during compaction. The dissolved minerals in the rock seep deep into holes and crystallize acting like a glue
How sedimentary rocks are classified:
1.
Detrital or Clastic
o Sedimentary rocks are made from broken pieces of other rocks.
o They have a granular texture.
o Named according to size and shape of sediments
a.
sediment size can be large like gravel or small like clay
b.
sediments can be well rounded or have sharp angles
2.
Organic rocks
Rocks that form from the remains of plants and animals which are deposited in thick layers
a.
coal forms from the remains of swamp plants buried in water
b.
chalk forms form the hard shells of living things
3.
Chemical rocks
Form when minerals that are dissolved in a solution crystallize
a.
can also form when mineral deposits are left when seas or lakes evaporate.
Metamorphic Rock Notes
The most important thing to remember is that these rocks are formed by the processes of HEAT AND PRESSURE!
How Metamorphic Rocks Form:
o Heat and pressure result from one layer of rock on top of another layer
1
1.)
sometimes temperature and pressure are great enough to melt rock, forming magma
2.)
sometimes pressure flattens mineral grains in rocks without melting them
o Every metamorphic rock is a rock that has changed its form – its appearance, texture, crystal structure, and mineral content change
o Metamorphic comes from the Greek words
1.)
meta meaning change
2.)
morphos meaning form
How metamorphic rocks are classified:
o Metamorphic rocks are classified by composition and texture
1.
Foliated rocks – rocks that have their grains arranged in parallel layers or bands, rocks can split along these layers
2.
Non-foliated – rocks whose grains are randomly arranged, do not split into layers
Rock Cycle
Earth’s constructive and destructive forces drive the rock cycle. Constructive forces build up and add to the Earth’s surface. Destructive
forces wear away and break down the Earth’s surface.
Erosion – is the process of wearing down and carrying away rocks. (breaking of rocks into smaller pieces and the removal of rock particles by wind,
water, ice, or gravity)
Weathering – is the process that breaks down rock and other substances. (heat, cold, water, ice, and gases all contribute)

Mechanical Weathering – rock is physically broken down into smaller pieces

Chemical Weathering – the process that breaks down rock through chemical changes
Both erosion and weathering involve the breaking down of rocks into smaller pieces, but erosion also involves the removal of rocks once they are
broken.
Erosion and weathering change Earth’s surface continuously, or without stopping. They are destructive forces that act to break and wear down the
surface.
______________________________________Geologic
Time_____________________________________
A.
Fossils are the preserved remains or traces of living things
1.
Form when living things die and are slowly buried by sediments that slowly harden into rock and preserve the shapes of the
organisms
2.
Usually found in sedimentary rocks
3.
Kinds of Fossils
a.
Petrified Fossils – minerals replace all or part of an organism; “turn it to stone”
b.
Molds and Casts – most common
1.)
mold – a hollow area in the sediment in the shape of an organism
2.)
cast – a copy of the shape of an organism if minerals and sediment seep into the empty space of a mold
c.
Carbon Films – a thin coating of carbon on rock
d.
Trace Fossils – provide evidence of the activities of ancient organisms, ex: footprints
e.
Preserved Remains – some processes preserve remains with little or no change, ex: tar, amber, freezing
4.
The Fossil Record – provides evidence about the history of life on Earth; shows how different groups of organisms have
changed over time
Age of Rocks
1.
Relative Age of rock is its age compared to the ages of other rocks
a.
law of superposition – oldest layer is at the bottom and each higher layer is younger than the layers below
2.
Absolute Age of a rock is the number of years since the rock formed
a.
radioactive dating – during radioactive decay, the atoms of one element decay into atoms of another element
b.
This shows the age of the oldest moon rocks, so scientists infer that the Earth is a little older than those rocks – about
4.6 billion years old
The Geologic Timeline – a record of the life forms and geologic events in Earth’s history
1.
Precambrian Time – where geologic time begins, covers about 88% of Earth’s history, ended 544 million years ago
2.
Eras – the time between Precambrian and the present are divided into three long units
a.
Paleozoic – began about 544 million years ago and lasted 300 million years; many animals were
invertebrates (no backbone) in this era; “paloe-“ means ancient or early and “-zoic” means life
b.
Mesozoic – began about 245 million years ago and lasted about 180 million years; the Age of the Dinosaurs
and mammals began to evolve; “meso-“ means middle
c.
Cenozoic – most recent era; began about 65 million years ago and continues to present day; the Age of
Mammals; “ceno-“ means recent
3.
Periods – these are subdivided eras and are characterized by what life existed worldwide
4.
Epochs – further subdivided periods of the Cenozoic Era because the fossil record of this era is more complete and
there are a lot more events to place in sequence.
B.
C.
Atmosphere/Water Cycle/Weather/Clouds/Climate
1.
Layers of the Atmosphere:
2
Troposphere - lowest layer; where weather occurs; contains 90% of gases that make up the atmosphere
Stratosphere - contains the ozone layer which helps to absorb UV radiation
Mesosphere - middle layer; coldest layer; where meteors burn up
Thermosphere - very hot layer; contains the ionosphere which radio waves bounce off of
Exosphere - outer layer; where satellites orbit; the beginning of outer space
2. Jobs of the atmosphere: absorbs energy form the sun; recycles water; provides a moderate climate; protects us from radiation;
protects us from the vacuum of space
3. Gasses in the atmosphere: Nitrogen (78%), Oxygen (21%), Water Vapor (about 1% but amount varies)
4. The three types of heat transfer:
Radiation the transfer of heat through rays or waves (ex: getting a sunburn)
Conduction the transfer of heat through direct contact (ex: touching a hot iron)
Convection the transfer of heat through a cycle or a flow of material (ex: boiling water)
5. Steps of the Water Cycle:
Evaporation water changes from liquid to gas (water vapor) when heated by the sun
Transpiration water evaporates through openings in plant leaves
Sublimation ice changes directly into water vapor without first becoming a liquid
Condensation when water vapor in the atmosphere cools it changes back into a liquid forming clouds
Precipitation when the clouds can no longer hold the liquid water it falls back to the Earth as rain, sleet, snow or hail
Infiltration when water sinks into the ground through small spaces in soil or rocks
Groundwater water below the surface
Sun the source of energy that drives the water cycle
Hydrosphere all of the water on Earth’s surface
6. Weather is the short term condition of the atmosphere over a small area
7. Air pressure is the force of the air that presses down on Earth and is measured using a barometer
8. Relative humidity is a comparison of the actual amount of water vapor in the air with the maximum amount the air could hold at that
temperature and is measured using a psychrometer
9. Wind speed is a measure of how fast the air is moving and is measured using an anemometer
10. Wind direction is the direction from which the wind is coming from.
Notes: Air Masses and Predicting the Weather
1. Air Masses move across the land or oceans; they meet but do not mix
2. Five major air masses affect the weather across the U.S. (maritime tropical, continental tropical, maritime polar, continental polar, continental
arctic)
3. In North America, most air masses move from west to east. The jet stream is a band of high-speed wind about 10 kilometers above the surface
of Earth that pushes air masses along.
4. A front is where air masses meet and collide. A boundary forms between the two air masses. Sudden changes in weather conditions can occur
as a front passes.
5. There are four types of fronts:

Cold front- moves quickly, brings rain, temperatures get cooler.

Warm front -moves slowly, brings rain, temperatures get warmer.

Stationary front- warm and cold air masses meet but neither is strong enough to move the other; can bring many days of precipitation.

Occluded front -warm air mass is caught between two cold air masses; warm air is cut off from the ground
6. High and Low Pressure Systems: High - brings clear skies and dry weather; Low – brings cloudy, wet weather
7. Climate is the average year-after-year conditions of temperature, precipitation, winds, and clouds in an area
8. Clouds:

Height- Cirro- high; Alto- middle; Strato- low

Shape- Cirrus- wispy and feathery; Stratus- spread out; Cumulus- puffy and fluffy

Rain- Nimbus
Notes: Air Movement
1. Flow of air is caused by solar radiation and the Coriolis Effect
2. Areas of the Earth receive different amounts of radiation because earth is curved

The equator receives more radiation

Areas near the north and south, the sun’s energy strikes at an angle, spreading out the energy
3. Coriolis Effect – the rotation of Earth causes moving air and water to appear to turn to the right north of the equator and to the left
south of the equator
4. Belts of prevailing winds that distribute heat and moisture around the globe are called global winds. (Prevailing Westerlies, Doldrums, Trade
Winds, Polar Easterlies)
5. Sea Breeze – created during the day because solar radiation warms the land more than water
a. Air over land is heated by conduction and rises
b. Cooler, denser air flows toward the warmer, dense air
c. A convection current results, and wind blows from the sea toward the land
6. Land breeze – created at night, because land cools much more rapidly than ocean water
a. Cooler, denser air above land moves over water
b. Warm air over the water rises
c. Wind blows from the land toward the sea
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________________________________Sun-Earth-Moon-StarsPlanets_______________________________
A.
The Earth
1. Axis- imaginary vertical line around which Earth spins
2. Rotation– the spinning of Earth around its axis that causes day and night
3. Revolution– Earth’s yearly orbit around the Sun
a. Earth’s orbit is an __ellipse___, or elongated, closed curve
b. Because the Sun is not centered in the ellipse, the distance between Earth and the Sun changes during the year
4. Earth’s tilt causes seasons
a. The hemisphere tilted toward the Sun receives more daylight hours and radiation than the hemisphere tilted away from the Sun
b. The longer period of sunlight is one reason summer is warmer than winter
B.
The Moon
1. Motions of the Moon
a. ___Rotation___ on its axis which takes about _29.5_days, with the same side always facing Earth.
b. Shines because it reflects sunlight
2. Phases of the Moon
a. _New Moon____– the moon is between Earth and the Sun and cannot be seen
b. __Waxing______– more and more of the lighted side of the moon can be seen each night (waxing crescent,
first quarter, waxing gibbous)
c. __Full Moon____– all of the moon’s lighted side is visible
d. __Waning____– less and less of the lighted side of the moon can be seen each night (waning gibbous, third
quarter, waning crescent)
3. Eclipses – when the Earth or the Moon casts a shadow on the other
a. Solar Eclipse - the moon moves directly between Earth and the Sun, shadowing part of Earth; occurs during the day ;
during a new moon
b. Lunar Eclipse - the Earth’s shadow falls on the moon; occurs at night ;during a full moon
4. Tides - at any shoreline on Earth, the height of the water will rise and fall throughout the day. Gravity is responsible for these
regular increases and decreases.
a. The moon’s gravity pulls on Earth.
1.) This pull creates a bulge of water on the side of Earth facing the Moon.
2.) Earth’s rotation and inertia creates a bulge on the opposite side of Earth as well
3.) The two bulges create high tides and between the two bulges are low tides.
b. The sun’s force on the tides is less than half of the effect of the Moon.
1.) It creates two additional bulges
a.)
Spring Tide - the sun, moon, and earth align during a new and full moon and high-tide waters are
higher than normal
b.)
Neap Tide - when the moon is in the first or third quarter and high tides are lower than normal and
low tides are higher than normal
C. The Sun
1. Solstice - the day when the Sun reaches its greatest distance north or south of the equator
a. Summer Solstice - occurs June 21 or 22 in the northern hemisphere
b. Winter Solstice - occurs December 21 or 22 in the northern hemisphere
2. Equinox - the day when the Sun is directly over Earth’s equator
a. Daylight and nighttime hours are equal all over the world
b. Spring Equinox occurs on March 20 or 21 in the northern hemisphere
c. Fall Equinox occurs on September 22 or 23 in the northern hemisphere
D. Life Cycle of Stars
1. Nebula – how a star begins as a large cloud of gas and dust; gravitational force causes the nebula to contract; it breaks into smaller
pieces when gas and dust become so hot that nuclear fusion starts; A STAR IS BORN. Stars spend many years in a relatively constant
state. The center shrinks, and the outer part of the star expands
2. All average stars, including our Sun, eventually becomes a Red Giant.
3. Planetary Nebula – the outer part of the red giant grows larger until it eventually drifts into outer space.
4. The hot outer core left behind is a White Dwarf. A white dwarf is about 1 million times as dense as the Sun. Most of its fuel is gone,
so it not longer produces energy. It gives off enough leftover heat to glow faintly for perhaps a billion years. It continues to cool until it
becomes cold and dark. It is then called a Black Dwarf.
5. If the star is a massive star, it becomes a Supergiant.
6. The core eventually collapses violently, sending a shock wave outward through the star. The outer portion explodes producing a
Supernova. This can be million of times brighter than the original star.
7. Material left from a supernova is called a Neutron Star. These are about twice as massive as the Sun and very dense.
8. If material left over from the supernova is more than three times as massive as the Sun, it becomes a Black Hole because the core
collapses. The gravity from this mass is so strong that nothing can escape from it, not even light.
Stars take different lengths of time to go through their life cycle. The length of a star’s life depends on its mass. The most massive stars live the
shortest lives because they use up their fuel more quickly than stars with less mass. The life cycle of a star is often compared with that of the
Sun, which is an average star. In about 5 billion years, the Sun will become a giant. Now, our Sun is a main sequence star, between an average star
and a red giant. The Sun has an expected lifetime of about 10 billion years.
•
All stars are huge spheres of glowing gas. Made up mostly of hydrogen, stars produce energy through nuclear fusion.
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•
•
Stars are classified according to color, temperature, size, composition, and brightness.
The brightness of a star is described in two ways:
1. apparent magnitude – is a star’s brightness as seen from Earth
2. absolute magnitude – is the brightness the star would have if it were a standard distance from Earth; actual brightness
Main Sequence- diagonal band on H-R diagram (about 90% of stars)
* Upper Left – hot, blue, bright stars
* Lower Right – cool, red, dim stars
* Middle – average yellow stars like the Sun
The other 10% are dwarfs, giants and super giants.
The inner planets are small, solid, rocky, and have iron cores, warm, few to no moons. The outer planets are large, lightweight, and gaseous,
colder, have many moons and rings. (review your notes on the planets)
_____________________________POSSIBLE SHORT ANSWER
QUESTIONS___________________________
1. Explain why it is warmer near the equator than it is near the poles.
2. Describe what happens to an average star and a massive star when each runs out of fuel.
3. Describe the source of energy for the forces that move the Earth’s plates.
4. Explain why the oceanic plate travels beneath the continental plate instead of the two plates smashing
together and buckling.
5. A geologist finds an area of undisturbed sedimentary rock. Which layer would be the oldest and how would
he/she know it’s the oldest?
6. How would a metamorphic rock change into an igneous and sedimentary rock on the rock cycle?
7. What is the theory of plate tectonics and what causes it?
8.
Label the phases of the moon.
9. Name and describe the three types of plate boundaries.
10. What is the difference between a lunar and solar eclipse?
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Answers to the short answer questions:
1.
The areas around the equator get more direct sunlight/radiation from the sun and therefore, those areas
around the equator are warmer.
2. The star collapses under the force of its own weight. Very massive stars can go supernova and leave
behind a neutron star or black hole. Small or average-sized stars (like our Sun) leave behind a white
dwarf.
3. The source of energy that move the Earth’s plates are convection currents.
4. The oceanic plate is more dense, therefore, it will travel beneath the continental plate.
5. Due to the law of superposition, the oldest layer is at the bottom and each higher layer is younger than
the layers below.
6. Metamorphic rock forms due to heat and pressure. In order for metamorphic rock to change into
igneous rock, the rock would go through a cooling process and become igneous rock. The igneous rock
would become sedimentary rock through a process of weathering and cementation.
7. The theory of plate tectonics is when the Earth’s crust and upper mantle are broken into plates, or
sections, that move around on a plasticlike layer of the mantle.
8. New moon, waxing crescent, 1st quarter, waxing gibbous, full, waning gibbous 3rd quarter, and waning
crescent.
9. Convergent boundary-when plates move together, divergent boundary-when plates move apart, and
transform boundaries- plates slide past one another
10. Lunar eclipse occurs when earth passes directly between the Sun and the Moon and earth’s shadow falls
on the Moon. Solar eclipse occurs when the Moon passes directly between the Sun and Earth and casts
a shadow over part of Earth.
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