Download There was a very important event that occurred early in Earth`s

3. There was a very important event that occurred early in Earth’s history. Do you remember what it is
called? What happened during that event? (hint: there are around 6 or so major changes to the
Earth that occurred)
a. The Iron Catastrophe!
i. The Earth became differentiated (layered)
ii. Dense material “sank”; iron migrated downwards to form the core, and silicate minerals
floated to form the crust and upper mantle
iii. A crust formed as magma oceans of the Earth cooled
iv. Outgassing; volcanoes expelled gases like CO2, H2O
v. The atmosphere formed from these gases
vi. The hydrosphere (ocean) formed as a result of H2O condensing in the atmosphere and
precipitating
vii. The biosphere (life-containing “layer”) resulted
4. Draw a large circle (or semi-circle) that represents the Earth. Then draw in the continental crust,
oceanic crust, mantle, and core. What type of material (rock or element) is each layer mostly made
of? What are the most common elements in the crust? In the Earth?
a. The core is made of iron-nickel
b. The mantle is largely peridotite (an ultramafic rock)
c. Oceanic crust is made of basalt (mafic)
d. Continental crust is made of granite (felsic)
7. Pretend you are a geologist (unless, of course, you would rather be a student who simply wants to
pass the class…but who doesn’t like rocks?!). You take a sample of a basalt flow and send it to a lab.
You find that there is 6.25% of a parent isotope left, and 93.75% daughter isotope. You know that
the half-life for this isotope is 50my (million years) old. How old is this basalt? What Era is this?
What Period? Try changing around the numbers (i.e. 12.5% parent, HL = 120my) and try the
problem again.
a. Remember that you started with 100% of the parent isotope/rock.
b. After one half-life (how long it takes for half of the isotope to decay), there would be 50%
parent and 50% daughter. Two half-lives: 25% parent and 75% daughter. Three half-lives:
12.5% parent and 87.5% daughter. Four half-lives: 6.25% parent and 93.75% daughter.
c. So if four half-lives have passed, and each half life take 50my, multiply 4*50=200my. The
basalt is 200my old. This would place it in the Mesozoic Era, specifically the Jurassic Period.
9.
(This is a long one!) There are two types of atomic bonding we talked about in class. What are
they, and what is the definition of each? What makes them different from each other?
a. Define cation and anion.
i. A cation is a positive ion, an anion is a negative ion. I write my ‘t’ like a plus sign, so
think of ca(+)ion. Then think of ‘i’ as being a sideways negative sign. An(i)on.
b. You know that Si (silicon) has a +4 charge, and O (oxygen) has a -2 charge. What type of
bond would they make? Which would lose an electron(s), and which would gain
electron(s)?
i. They would make an ionic bond
ii. Silicon would lose 4 electrons to become a positive cation, and each oxygen would
gain 2 electrons to become a negative anion.
c. What important rock-forming compound have you just created? Draw a diagram of the
compound.
i. (SiO4)-4, the Silica Tetrahedron