The Geology 101 series is an idea I’ve been kicking around for some time now. The reason for this is two-fold: to communicate the basic underpinnings of geology to the public and to keep those concepts fresh in my mind as I continue my own studies. However, it seemed like such a massive undertaking that I wasn’t sure where or how to start such a task, so I put it on the back burner. And then, my dear friend Dana wrote this. (I’m not going to summarize her excellent post because I can’t do it justice. Just read it and thank me later).
I knew I had to dust off the Geology 101 series, not just for Dana, but for all those who want to learn more about the earth and its comings and goings. I’m still unsure on how to convey the grandeur of the earth sciences, but I have my trusty Essentials of Geology by Stephen Marshak to give me some ideas. I’m planning for this to be once a week like Meteorite Monday, but that could change depending on my school/work schedule. With that being said, let’s get to the fun stuff!
We’re going to start at the beginning- not with the formation of the earth, nor the solar system, but the universe itself. This may seem like a strange starting point, but you need an idea of how it all truly began to appreciate how the earth came to be. 14 billion years ago (and not 6,000 like some cranks teach), soon after the Big Bang, there existed a whole lot of hydrogen, some helium and probably a smidgen or two of lithium floating about. These atoms formed the first stellar nurseries, what are commonly referred to as nebulas. Of course, it’s much more complicated than that, but I’m not an astrophysicist so I’m not going to delve into the details. So, if you want a better explanation I’m going to suggest you watch this video from our friend Carl Sagan.
These nebulas began to churn out the first round of stars. As these stars grew, they began to form heavier elements. At the end of their life-cycles, these stars became supernovas. Stephen Marshak writes that this violent end is how elements heavier than iron are formed (P.16). As the stars went supernova, the elements were peppered all across the solar system. Then the process repeated. More stars formed, created heavier elements and became supernovas just like the previous generation. This continued on and still continues today. This is the material from which we and our earth were formed. To quote Carl Sagan “We are all made of stardust”.
Approximately 8 billion years after the Big Bang our solar system began to take shape. At this point it was just a huge disk of gravity bound dust and ice that circled around our proto-star. This is referred to as an accretionary disk or protoplanetary disk and can actually be found throughout the universe.
Gravity began to pull this space dust together and form planetesimals (or baby planets, if you will), in a process called accretion. These nascent planets grew by sweeping up other pieces of rocky material in their path. A few of those planetesimals grew large enough to develop iron cores in a process called differentiation. Wanna hear something really interesting? As I’ve mentioned in other posts, iron meteorites represent the core of these planetesimals. Currently, there are 26 different types of iron meteorites and some researchers have suggested that these came from 26 distinct planetesimals.
However, most of these planetesimals didn’t survive the turbulent beginnings of the Solar System. In a game of galactic bumper cars, the planetesimals collided with one another and broke apart. Some of this material reaccreted (or came back together) to form brecciated asteroids such as Itokawa. All this left over building material can be found in the asteroid belt, a planetary graveyard of sorts.
I’m not going to speculate much on the formation of the gas giants. That’s beyond the scope of this post, but I will leave you with some nice tidbits of info that I’ve picked up in my studies. It’s been suggested that the formation of Jupiter could be responsible for Mars’ stunted growth. Any material that Mars could have swept up to increase its size was taken by Jupiter’s immense gravitational influence. This would suggest that Jupiter probably had a head start in its formation if it had sufficient gravitational force to sweep up the potential building blocks of Mars. But this is all speculation so, if your curiousity is piqued, I would suggest starting with Wikipedia to suss out some of the material.
So, with the creation of our Solar System, and subsequently our earth, out of the way I’m going to wrap up this first installment of Geology 101. Feel free to leave your questions or even suggestions for future topics in the comment section below.
More resources for learning:
1. Iron meteorites as remnants of planetesimals formed in the terrestrial planet region. (subscription required or possibly an #icanhazpdf plea on the twittersphere)
2. The Big Bang (from Wikipedia)
3. Cosmos (Hulu has the entire series. There’s really no excuse to not watch it)
4. Solar System Formation (A well put together, easy to understand website)