Earth’s History Unit Test 1 Study Guide
Earth’s interior structure is divided into layers because the materials inside of Earth have different _____densities______.
The four main layers from the outer most to the inner most are the ____crust___________, ____mantle__________,
_______outer core___________ & ______inner core___________.
The ___lithosphere___________________ is made up of the crust and the solid upper portion of the mantle and sits on top
of the liquid portion of the mantle known as the ________asthenosphere____________________. The layer that is
broken into tectonic plates is the _________lithosphere____________________.
The Law of __Uniformitarianism________ states that Earth is _________always____ changing, by the same
__forces__________. Some changes are gradual and some are _____fast_________.
German scientist ________Alfred Wegener____ _____________ hypothesized that Earth’s continents were once connected
into one supercontinent called ___Pangaea____________ and that they slowly moved apart which is why his theory is
called The Theory of _________Continental Drift_______. Several pieces of evidence helped support his theory such as
___________continents fit like puzzle pieces, matching rock layers, matching fossils, evidence of climate change, seafloor spreading, mid- ocean ridge _________________________________.
Exploration of the sea floor helped support this later as a geologist named _Harry Hess___ realized that new
____crust_____ was being formed at _divergent_______________ boundaries as _magma__________ was rising up
and cooling, creating a feature on the ocean floor known as a _mid-ocean ridges___________. The rock closest to the
crack was the ___youngest_____________ and the rock farther from the crack was __oldest______________.
Even though new crust is being formed when _sea-floor________ spreading occurs, the Earth doesn’t get any bigger
because crust is being ___recycled_____________ at __convergent_______________ boundaries where
_____subduction_________ is occurring, or one plate is sinking beneath another plate.
Scientists also discovered that __minerals_________ in the magma aligned itself with one of the Poles and sometimes
caused the North and South Pole to switch. This strange occurrence is called _magnetic reversal______ ____________.
A “plate boundary” is a very general term for where __2___ plates meet, but there are really 3 specific types of boundaries:
__convergent________________, ____divergent______________ & ____transform________________. Different
landforms are formed at each type of boundary based on the directions the plates move. _Convergent___ = collide,
_____Divergent________ = divide, and ____Transform______________ = slide.
_Earthquakes can occur at any type of boundary whenever there is plate movement, but are most common at
___transform_________________ boundaries along with large cracks called _faults_______________.
At ____divergent____________ boundaries, ____rift_____ valleys, __mid-ocean_____ ridges, __new______ crust, &
_volcanoes___ form.
At __continental-continental___ convergent boundaries, _hig___mountains form. At _oceanic -oceanic__________
convergent boundaries, deep _ocean____ _trenches____ & __volcanic___________ islands form. At ___oceaniccontinental____ boundaries, deep ocean trenches and ___coastal____________mountains form.
Sometimes other features can form __far______ from plate boundaries where magma rises and melts the crust above. This
is called a ___hot______ ___spot_______. __Hot________ __spots________ stay in one place while the plate moves
across the top of it allowing __island_________ chains like Hawaii to be formed.
Earth is approximately ___4.6_____ billion years old, but how do we know?
_Fossils_______ are traces or remains of living things from long ago. These are created over long periods of time, only
when the conditions are just right. Remember, MOST organisms die and decay without leaving a trace of their
existence; so discovering one of these is pretty cool, and very ____rare_______.
_Index_______ ____fossils_____ are used as a reference because they are animals or plants that were known to exist at a
very _specific__________ time, in a very specific __location__________. They are useful for estimating the age of the
_layer_______ they were found in.
In addition to fossils, __ice______ ___cores_____ and __tree______ __rings______ are types of natural evidence that
are used to study Earth’s past, especially the __climate_________. Tree rings vary in width, according to the tree’s
yearly _growth___________. Thick rings indicate a _good______ year of growth, while thin rings indicate a
_poor________ year of growth due to environmental conditions such as the amount of _rainfall_______.
Ice cores are __tubular__________ samples of layers of snow and ice that can be used to analyze past events by using the
things found frozen inside of them such as ___ash___, ___sediment_________ and ___pollen_____ just to name a few.
Layers of sedimentary rock show general, or __relative______ age because they form in horizontal layers, with the
___oldest______ layer on the bottom and the __younges_______ layer on the top. This idea is called the Law
of___Superposition______________.
When the layers may no longer be in the correct order, or are missing information that is called an
___unconformity________. Examples are Igneous rock __intrusions_______ that cut through sedimentary rock,
making the igneous rock __younger________ than any layers it cuts through. Other examples of include when the rock
layers fold or _____overturns________________ and when the layers actually shift or crack due to a
_fault___________ which are usually caused by ______earthquakes_______________.
____Radioactive______ _dating_______ is a process that can show absolute age. This process involves using the rate of
change of a radioactive element, or its _half-life _______. This process can be used to date items that were never
___alive________, or items that are extremely ___old_______. While ___carbon_- dating can only be used for items
that were once _alive_______, and do not pass the age of __60,000_______ years.
The ____Geologic Time Scale ____________divides Earth’s history into intervals defined by __catastrophic events_or
changes on Earth. The 4 divisions of time from largest to smallest are: ____eon______, ____era______,
____period________, _____epoch_______.
For the first 4 billion years of Earth’s history, Earth had no plants or animals – only volcanic ash, dust, and single-celled
organisms. This was known as ___Precambrian______________ Time.
The “Age of Amphibians,” or The ___Paleozoic____________ Era, is when all life lived in the ocean until the end when some
creatures started to move onto _land________.
The “Age of Dinosaurs,” or The ___Mesozoic_______ Era, was when the dinosaurs lived along with flowering plants, birds,
and the first mammals. This era ended with a _meteor strike_____ off the coast of ___Mexico______ that blocked out
the ____sun__________.
The “Age of Mammals,” or The __Cenozoic___ Era, is the current era. Many important things happened such as the major
climate changes of the ___ice ages_______ and the first __humans______ appeared as well.
In general, throughout the Geologic Time Scale life forms went from __simple_____ to more complex. Humans have only
been here for a very small portion of Earth’s History!
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