Geology of the Solar System 1: Origins of the universe, the elements, and our solar system


The exam for my geology of the solar system is fast approaching, so I’m putting together some blog posts on the materials to help me study. But first, a few notes about my notes:

They will be a hundred times more awesome if you can get your hands on a pair of anaglyph 3D glasses.


Red goes over the left eye. Blue goes over the right eye.

A number in brackets indicates the presence of a footnote.

This stuff barely scratches the surface, and it doesn’t even contain everything that’s in my class notes. This is because a. I don’t want to bore you, b. I don’t want to bore myself, c. I only want to focus on the main points I need to know for the exam for the sake of saving time and energy, d. I don’t think my professor would appreciate me posting almost verbatim his class notes.

I’m following the scientific, not the religious, aspect of this topic (there will likely be at least a few mentions of things like the Big Bang and the Solar Nebula Hypothesis), because that is what is dealt with in my class, my notes, and the upcoming exam. Deal with it.

Now, onto the notes!

Some general context

I’m going to blast through this stuff, providing only the most general of information, as I don’t particularly need it for the exam and it can get pretty tedious if you are only a partial nerd about this stuff, as opposed to a complete nerd.

The matter of the universe is subdivided/collected into galaxies.
Ours is called the milky way, and is a spiral galaxy like this one, NGC 300 (1).
anaglyph spiral galaxy NGC 300
To put this into context, galaxies come in many shapes and sizes (2).


Here’s a fun, short video to segway from galaxies to the next topic.

The origin of the universe and the elements

The universe originated between 14 and 13 billion years ago (when talking about dates in the past, the oldest are mentioned first) with a Big Bang. This age has been determined using two methods: by assuming everything originated at a single point and began expanding outward, we can measure distances and rates of separation; we can also measure the cooling rate of white dwarf stars. Both of these methods come out with similar numbers, so it seems reasonable to assume that this time frame is correct.

Galaxies were formed from the hydrogen, helium, and neutrons present after the Big Bang by mutual gravitational attraction. When such attraction becomes strong enough, stars are formed and additional elements are created by hydrogen burning which, for the sake of holding your attention, I won’t describe here.  You can, however, watch this short video about the life cycle of a star. The dramatic ending is priceless.

The heavy elements that make up our solar system were created by other stars at the end of their life cycle, not by ours.

The origin and age of our solar system

The currently accepted theory is called the solar nebula hypothesis.

(This is a nebula)

anaglyph nebula
As gravitational contraction of nebular gas and dust occurred, collision of matter increased and concentration of matter increased, producing heat, increasing gas pressure, and retarding collapse/contraction. Rotation produced a disk of matter in the equatorial plane, which led to the formation of planets and other bodies.


This explains why the planets all rotate on the equatorial plane.

Eventually It got hot enough for hydrogen burning to begin.

Over time the hot nebular gas began to cool and condense into solid materials over a huge range of temperatures. In general, elements that can condense at high temperatures form materials closer to the sun, and those that condense at low temperatures form materials farther from the sun, hence the planets close to the sun are rocky (called terrestrial planets) and those farther from the sun are gassy (called Jovian planets).

(Objects in picture are not to scale, and Pluto is not a planet)

It is thought that the planets were formed by cold accretion. This process involves solid (not molten) grains of materials collecting together by mutual gravitational attraction to form planetesimals, which would have eventually become hot and molten as a result of the incredible heat generated by gravitational and frictional energy during the accretion process.

There are of course some problems with this theory.
First, as you may have noticed in your own life, solids colliding at high velocity tend to fragment and break each other apart, not stick together.
Second, for accretion to be possible there must be very small velocity differences between the particles coming together in order for it to work.
Third, the small gravitational fields of the small particles planet formation would have started out with would mean that said particles would have to be extremely close together in order to act gravitationally upon each other.
In other words, the whole process seems a bit unlikely, but it’s the best idea we currently have, and it’s not impossible.

All the same, planets were formed. Hooray!

Assuming a common origin of all planets and other bodies in the solar system, meteorites should be able to help us determine the age of the earth by virtue of being the same age as solid materials in the solar system, so that’s what we use. Radiometric dating of meteorites called carbonaceous chondrites help us determine how old the solar system, and therefore the earth, is.


(Radiometric dating in my mind)

half life

(Radiometric dating in reality)

The oldest dated material in the solar system is about 4.56 billion years old.

And now we have some sort of foundation off of which to base our understanding of the geology of the universe.

Now onto the planets! Yay!


1. The 3D pictures of outer space came from You can go there to look at much larger versions of the images in this post, as well as many others.  I highly recommend it if you are wanting to have your mind blown today.

2. You can view a large, high resolution version of the picture of the different types of galaxies here:


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