EPSC201 - Lecture 4 Notes
Creating a galaxy and creating a solar system are similar. The disk of mass is rotating; the gravity pulls
the mass to- wards the center, which forms a sun or a black hole.
The rings spinning around the sun will become the planets.
There are separate rings. The larger particles are
dragging in the smaller ones, which makes
them even bigger. These particle clumps are
called partitesimals. The composition in
each each ring will be different. The ring
is colder on the outside, hotter on the
inside. That makes certain gases con-
dense at different distances. Olivine
and iron condense around 1800 Celcius
which forms metallic iron and olivine. The snowball goes around and
gathers more dust, making planet earth. Going further out, the tempera-
ture drops lower, making water vapour condense into liquid and ice.
Carbon dioxide become solid at -56 Celsius and is dry ice. Methane be-
comes solid at -182 Celsius. Ammonia is also a composition of the gas planets. The
gas planets are actually not gas, but solids that would be gas on Earth. The inner core of gas giants con-
tain elements that would be on earth, such as iron and olivine. The lighter elements like methane and wa-
ter are on the surface, and make up a large part of the planet.
If the object is fairly small, it will have an odd potato shape. The larger it is, the more gravity there is to pull
it into a sphere. Gravity slowly shapes the object into a sphere. Planets are effectively spherical, some of
the smaller moons on Mars and Jupiter are not spherical.
Io, one of the moons of Jupiter, is the
most active ob-
ject in our
There is lots of
Almathea, formed 4.6 billion years ago,
has craters because the surface is not active like Io is. Almathea
is also a moon of Jupiter. Earths Moon has not had much volcanic activity for
about 3 billion years.
Our moon is the result of the collision of Earth with another object about the size of Mars, the heavier
parts of the incoming planet joined into the Earths core, and the outer part of the Earth got melted along
with the lighter parts of the incoming planet. A lot of the material got put into orbit, which eventually be-
come the moon. The force of gravity took over and snowball effected. Points of Evidence
1. The Moon does NOT have an iron core, it is much less dense then the Earth. If you exclude the core
of Earth, the densities are similar. Both about 3.1 g/mL dense. THE MOON DOES NOT HAVE A
2. The isotopic ratios of the Moon and Earth are the same.
Earth also has lots of material from Mars due to meteorites. It is isotopically different then Earth and lunar
material. This also supports the collision theory for the formation of the moon.
Pluto was demoted in 2006 from a planet to not. Its orbit does not fit in line with the disk orbit of the other
planets. It is now officially a dwarf planet. Pluto has five moons. It now joins other dwarf planets in the
Iron and Oxygen dominant the chemical composi-
tion of Earth. In the core there is a lot of Iron and
Olivine (Fe,Mg)2SiO4 Olivine has lots of oxygen.
Magnesium and silicon are part of olivine.
The Composition of the Crust:
The crust varies from 6-70 km deep, which isn’t that deep.
A good analogy of the Earth is that it is like an egg. The yolk is the core. The shell is the crust. and the
egg white is the mantle. The outside is brittle, but the inside is ductile like a hard boiled egg.
Iron core, olivine surrounds core.
The core is the most dense part of the earth, 15 g/mL. The mantle is much less dense, about 3.3 g/mL .
Professor said not to memorize numbers, just have a rough idea. The outer crust is much less dense the the core, about 2.5 g/mL.
Volcanoes give clues about the composition of the mantle. Volcanoes can go up to a couple hundred km,
melting grabs a piece of mantle and brings it up to the surface. These pieces are called xenoliths. (for-
eign bits of rocks) The volcano is erupting foreign pieces of rock from the mantle. A good example is dia-
monds. Diamonds come from considerable depth in the mantle. They come from about a 100 km deep
but they get carried up towards th