CSET Practice Test Subtest II Science

The Earth's Layers

The Four Layers
The Earth is composed of four different layers. Many 
geologists believe that as the Earth cooled the heavier, 
denser materials sank to the center and the lighter 
materials rose to the top. Because of this, the crust is 
made of the lightest materials (rock- basalts and 
granites) and the core consists of heavy metals 
(nickel and iron).

The crust is the layer that you live on, and it is the 
most widely studied and understood. The mantle is 
much hotter and has the ability to flow. The Outer 
and Inner Cores are hotter still with pressures so 
great that you would be squeezed into a ball smaller 
than a marble if you were able to go to the center 
of the Earth.

The Crust
The Earth's Crust is like the skin of an apple. It is 
very thin in comparison to the other three layers. 
The crust is only about 3-5 miles (8 kilometers) 
thick under the oceans(oceanic crust) and about 
25 miles (32 kilometers) thick under the continents 
(continental crust). The temperatures of the crust 
vary from air temperature on top to about 1600 
degrees Fahrenheit (870 degrees Celcius) in the 
deepest parts of the crust. You can bake a loaf of 
bread in your oven at 350 degrees Fahrenheit, at 
1600 degrees F. rocks begin to melt.

The crust of the Earth is broken into many pieces 
called plates. The plates "float" on the soft, plastic 
mantle which is located below the crust. These 
plates usually move along smoothly but sometimes 
they stick and build up pressure. The pressure 
builds and the rock bends until it snaps. When this 
occurs an Earthquake is the result.

The crust is composed of two basic rock types granite 
and basalt. The continental crust is composed mostly 
of granite. The oceanic crust consists of a volcanic 
lava rock called basalt. Basaltic rocks of the ocean 
plates are much denser and heavier than the granitic 
rock of the continental plates. Because of this the 
continents ride on the denser oceanic plates. The 
crust and the upper layer of the mantle together make 
up a zone of rigid, brittle rock called the Lithosphere. 
The layer below the rigid lithosphere is a zone of 
asphalt-like consistancy called the Asthenosphere. The 
asthenosphere is the part of the mantle that flows and 
moves the plates of the Earth.

The Mantle
It is the largest layer of the Earth, 1800 miles thick. The 
mantle is composed of very hot, dense rock. This layer 
of rock even flows like asphalt under a heavy weight. 
This flow is due to great temperature differences from 
the bottom to the top of the mantle. The movement of 
the mantle is the reason that the plates of the Earth 
move! The temperature of the mantle varies from 1600 
degrees Fahrenheit at the top to about 4000 degrees 
Fahrenheit near the bottom!

Convection Currents
The mantle is made of much denser, thicker material, 
because of this the plates "float" on it like oil floats on 
water.

Many geologists believe that the mantle "flows" because 
of convection currents. Convection currents are caused 
by the very hot material at the deepest part of the 
mantle rising, then cooling, sinking again and then heating, 
rising and repeating the cycle over and over. The next 
time you heat anything like soup or pudding in a pan you 
can watch the convection currents move in the liquid. 
When the convection currents flow in the mantle they 
also move the crust. The crust gets a free ride with 
these currents. A conveyor belt in a factory moves boxes 
like the convection currents in the mantle moves the 
plates of the Earth.

Outer Core
The core of the Earth is like a ball of very hot metals. 
(4000 degrees F. to 9000 degrees F.) The outer core is 
so hot that the metals in it are all in the liquid state. 
The outer core is located about 1800 milesbeneath the 
crust and is about 1400 miles thick. The outer core is 
composed of the melted metals nickel and iron.

Inner Core
The inner core of the Earth has temperatures and 
pressures so great that the metals are squeezed together 
and are not able to move about like a liquid, but are 
forced to vibrate in place as a solid. The inner core begins 
about 4000 miles beneath the crust and is about 800 miles 
thick. The temperatures may reach 9000 dgrees F. and 
the pressures are 45,000,000 pounds per square inch. 
This is 3,000,000 times the air pressure on you at sea level!

The Life Cycle

Life cycle: The series of forms that an organism takes 
as it lives and reproduces.
All organisms have ways of growing up and reproducing. 
The forms that an organism takes during this process 
are called stages of the life cycle.

The Life Cycle of a Frog

Egg Stage:
Adult frog lays eggs in the water.

Tadpole Stage:
An egg hatches into a tadpole. Tadpoles swim in the 
water and breathe using gills.

Froglet Stage:
The almost mature frog, about 2 - 4 months old, still 
has some of its tail but can now breathe air using lungs.

Adult Frog:
The tail has been reabsorbed by the body.

The Life Cycle of a Butterfly 

The life cycle of a butterfly is arguably one of the most 
bizarre and impressive examples of nature at work on 
the planet - one could be forgiven for believing that 
caterpillars and butterflies were entirely separate species. 
They have very dissimilar features and not only feed on 
different parts of plants but usually, within the same 
species, on different actual plants. 

Egg Stage:
The tiny eggs reveal a variety of shapes under a 
microscope - they are laid by the female on the 
relevant foodplant, found by a combination of shape 
or colour recognition and chemical examination and 
then are abandoned by the parent.
Around 5 days later, a tiny wormlike creature will 
hatch.

Caterpillar Stage:
The newly emerged  caterpillar has biting jaws, six real 
legs plus a number of extra 'prolegs' but no compound 
eye.

It gets to work quickly devouring its food source and 
shedding its skin (a process called ecdysis) in order 
to grow. After usually four moultings, the skin removed 
reveals the chrysalis or pupa.

Some caterpillars spin a cocoon first but most just 
fasten themselves to a plant with a silken thread. 

Pupa Stage:
Although the pupa outwardly looks inert and resting, 
inside it is a bubbling cauldron of activity as the 
caterpillar is literally liquefied, then reassembled, over 
about two to three weeks, into a very different 
creature. It's is still not fully understood how this 
process occurs.

Some species hibernate in this state, although the 
transforming chemistry is suspended for most of the 
winter period in this case. 

Butterfly Stage:
The usual first evidence of the butterfly being ready to 
emerge is the translucency of the pupa skin showing 
the colouring of the wings beneath.

When the pupal skin splits, the limp, damp butterfly 
crawls out - now with compound eyes, a proboscis for 
feeding and very clearly six legs - the initially stubby 
wings are expanded by pumping blood into them and 
using gravity to help them enlarge. A little warming in 
the sun and it is ready to fly off to feed and mate.