Download Formation of Planets III

Formation of Planets III
Integrated Science
We have looked at general characteristics of the 4 inner and outer planets. We
found that the 4 inner planets have less ________ but a higher ____________.
This is because the solid material that inner planets formed from did not include
_____________ which are lighter but very abundant, whereas temperature
conditions during the formation of the outer planets were much ____________
so the abundant ices were solid and became part of the planets.
Today we will examine the composition of the 4 inner planets in more detail.
The densities of most rocks at the Earth’s surface are between _______ and
______ g/cm3. However, if we look at the overall density of the earth, the value
is approximately ______ g/cm3. There must be some density change beneath
the earth’s surface.
Smaller objects in space can give us some information. An asteroid is a rocky
object in space, varying in size from several meters up to about ______ km. An
asteroid group is a collection of asteroids moving in a similar orbit. Most
asteroids are found in a belt between _____________ and _______________,
although some are outside of this region, including some near-Earth asteroids.
A ____________ is a space rock that hits the earth’s atmosphere, sometimes
called a ____________. Most of these vaporize, but some reach the earth’s
surface. Those reaching the surface are called _______________. Most
meteorites are from parts blasted from asteroids that have collided with one
another. Meteorites are the oldest objects known and some are thought to be
pieces of the solar nebula that avoided incorporation into a planet, so they give
us information about the original material from which planets were formed.
Evidence for this is that some meteorites, _______________ meteorites, contain
spheres called _____________ of millimeter size that are thought to have
formed from liquid material in the solar nebula that solidified. A magnified
view of a chondrule is shown below.
Because the chondrules were once liquid, they formed around the melting
temperature of rock and metal, about 11000C. Material between the chondrules
in meteorites was often formed under different conditions. One type is called a
_______________ chondrite, which has a high carbon concentration between
the chondrules. The portion with the high carbon concentration could have
formed only under temperature conditions less than _________. Carbonaceous
chondrites have a composition of nonvolatile elements (elements other than
those which vaporize at low temperatures) that is identical to the nonvolatile
composition of the sun as determined by spectral analysis. Therefore, these
provide information to us about the elements that formed the _________ 4
planets.
The relative metallic abundance in chondrites is shown in the table below.
These abundances, then, give us some idea of the proportion of metals for the
inner planet’s compositions. These metals all combine with oxygen in forming
minerals, so oxygen is an important element. Looking at the mineral
composition of the chondrites provides some indication about the high density
of the inner planets. Some iron is combined with silicon to form silicate
minerals that are oxides (remember that silicate minerals have SiO4 as their
basic building blocks, other iron is combined with sulfur to form iron sulfides,
and other iron is by itself. Iron has a density of _______ g/cm3 while the others
have a density of about _______ g/cm3. Combinations of these can help explain
the density values for the inner planets.
There are meteorites that do not have chondrites are called ________________.
Some of these have a composition similar to volcanic rocks at the earth’s
surface. Others are primarily of solid __________ with some nickel mixed in.
These are probably from asteroids that were broken apart. If an asteroid has a
liquid iron silicate and iron mixture, the __________________ will float to the
top and the ________ will sink.
We can therefore explain the reason for the lower density of rocks at a planet’s
surface compared to the density of the entire planet. The sulfides and silicates
with the metals have a lighter density and are near the surface. The metals by
themselves are more dense and form the center or ___________.
The figure below summarizes the formation of the solar system:
There are two questions that remain to be answered. The first deals with
angular _______________. The sun contains 99.9% of the solar system’s mass,
yet, in looking at its slow spin speed, it has only 2% of the angular momentum.
The second question is that hydrogen and helium gas by themselves made up
the majority of the material away from the sun, yet, because they were a gas,
they would never become part of a planet (which only gathered ___________
material). Today, however, most space between planets has no elements, it is
empty. What happened to this gas?
A possible solution has been found from observations of the early stages in life
cycles of newly forming stars. Before the fusion of hydrogens to form helium
begins, the star emits a large wind, called a ________________, named after the
star where it was first observed. This wind would push out all the gas from the
solar system and also cause the spin of the sun to slow down.
We can now look at a list of the elements in the original nebular cloud and see
how they relate to Earth. The first is _____________. Most hydrogen was
either as a gas or liquid in the region of the inner planets, so for the most part it
was not part of the formation of our planet. Helium also was a gas, and should
not have been present. There is only a small amount of helium on earth today,
most coming from the _________________ decay of uranium and thorium.
Lithium, beryllium, and boron were not produced in significant amounts in
stars, so there abundance is minor. Carbon and nitrogen mostly joined with
hydrogen to form CH4, NH3, and CO, which were gases, so they did not form
the Earth. Oxygen readily combines with ______________, so it is abundant on
the Earth. Fluorine combined with hydrogen, and HF was a gas, so was not part
of the Earth’s formation. Also, Neon is a noble gas, so was not involved in the
Earth’s formation. Of the 10 first elements, then, 6 formed __________, so
were not involved in the earth’s formation, and 3 were not abundant in the solar
nebula, so are present only in minor amounts. Only _____________ is
abundant.
The next 5 elements are all _____________ and join with ____________.
Sodium is rather volatile, so is not very abundant. __________, ____________,
____________, and _____________ were in solid form, so were part of the
Earth’s formation. ____________ and ___________ are produced in greater
abundance that the other two elements in stars, so they are important. ________
and _______ are very abundant in the Earth.
Next is Sulfur. A significant amount of this was captured by ________, so it is
present in a significant amount on Earth. Most Chlorine and Argon were lost as
gases. Next are potassium, K, and calcium, Ca. Potassium is largely volatile,
so was lost. Calcium combined with oxygen, so is relatively abundant. Of the
second set of 10 elements, then, 5 (_____, _____, _____, _____, and _____)
were largely captured, 3 were partially captured (_____, _____, and _____), and
two were lost (_____ and _____). None of the elements between calcium and
iron were largely produced in stars, so they are not very abundant.
Remembering that ___________ was the last element to be produced in the
regular cycle in stars, it is available in abundance, close to magnesium and
silicon. After iron, the abundance drops off significantly, with only ______
fairly abundant.
One question that still remains, though, is to explain the presence of carbon and
hydrogen on the Earth today. Although we are not sure, it is thought that
shortly after the Earth formed there were many ___________ (the equivalent of
asteroids, but composed primarily of ices) that struck the earth. These would
provide the Earth a source of some of the more volatile elements.