The Origin of the Earth

Note: This blog post is taken from a series of posts that I originally posted on the Skepchick blog back in 2007. These posts came from a paper that I wrote for a Marine Geology & Geophysics class back in 2007, so the information here may be slightly out-of-date since the early Earth and Cosmos is a hot research topic. If you spot any errors (this is just a classroom paper, and I am not an early Earth expert) or want to add anything, please do so in the comments. Finally, I apologize that some of the figures do not have proper references. In my early blogging days, I stole figures and images from the interwebs with wild abandon. These days, I am more careful and try to reference sources. I eventually hope to go through this post and reference or replace the ambiguous figures. Most of the figures are hosted on image shack (I'll move them once I have fast, non-African internet again), so you may need an image shack account to view them properly. For now, I'll have to leave the post as is.  This post is long, but I've broken it up into 5 parts if you wish to digest it in pieces. Enjoy!

For the past couple of weeks [note: back in Spring 2007], I have been busy with final projects at school. For one of my geology classes I did a research project about the early Earth and Cosmos and wrote a paper on the subject, which I find fascinating. I thought some of the readers here might enjoy reading my early Earth paper, so I’m going to post it in installments along with appropriate images stolen from various websites and research articles. This paper is just a class research paper and is by no means comprehensive or perfectly polished, but I think many of you may enjoy it nonetheless.

The Origin of the Earth

Part I: Introduction, the Scientific Toolbox, and Cosmic Starstuff

The Cosmos is all that is or ever was or ever will be. Our feeblest contemplations of the Cosmos stir us; there is a tingling in the spine, a catch in the voice, a faint sensation, as if a distant memory, of falling from a height. We know we are approaching the greatest of mysteries; in the last few millennia we have made the most astonishing and unexpected discoveries about the Cosmos and our place within it; they remind us that humans have evolved to wonder, that understanding is a joy, that knowledge is prerequisite to survival. I believe our future depends on how well we know this Cosmos in which we float like a mote of dust in the morning sky.
-Carl Sagan, Cosmos

Introduction:
The study of the origin and development of the early Earth is one of the most intriguing and important research topics in science today. Understanding Earth's history in the context of the larger Cosmos is both awe-inspiring and humbling. Earth is but a tiny speck in the solar system and is dwarfed by the greater Cosmos. Yet, Earth is our home and harbors the only life of which we know. So, to us, study of the Earth-- both past and present-– is fascinating and also essential for our survival as a species. Psychologically, there is also something especially powerful about studying the early Earth. Just as we value learning about our ancestors and family histories, we value learning about the history of our planet. More practically, a better understanding of early Earth may provide information on how our planet will respond to stresses such as pollution, greenhouse gas emissions, and magnetic field reversal. Furthermore, if humans ever colonize planets in other solar systems, knowing what conditions and processes lead to an Earth-like planet may help scientists locate habitable planets. Study of early Earth is also relevant because today, at least in America, religious creationism has a strong hold in many places. Better understanding Earth's long history will aid those who confront the creationists and fight to teach valid science in our school systems.

The goal of this paper is to summarize the processes that scientists believe, to the best of their current understanding, led to the formation and development of the Earth. Because Earth formed from stardust, this paper will begin with an overview of nucleosynthesis, which occurs primarily in stars. The processes leading to the formation of various elements in the Cosmos will be described and trends in elemental abundances explained. Much information about Earth's history can be gleaned from a comparison of the abundances of elements in the Cosmos and solar system with the abundances of elements on Earth. Therefore, differences in the composition of the Cosmos, the sun, and the Earth will be noted and comments made about how elements are fractionated and concentrated in the solar system. Similarly, a general discussion of the solar nebula and the early development of the sun and solar system will be provided in order to put the Earth in a larger context.

Next, a brief overview of meteorites will be provided as Earth is believed to have accreted from planetesimals with compositions similar to meteorites, in particular carbonaceous chondrite meteorites. Understanding why and how geologists use meteorites to estimate the intial composition of the Earth is crucial to understanding the assumptions inherent in any geophysical or geochemical model using chondrite values for the composition of the early Earth. Following this discussion of meteorites, the accretion of the Earth from planetesimals will be discussed. The importance of late-stage collisions between large planetesimals will be emphasized. At the same time, the origin of the Moon from Earth via a Mars-sized impactor will be examined. Theories about a magma ocean that may have formed as a result of this giant impact will be presented as this magma ocean may have played a significant role in the differentiation of Earth's iron core.

Finally, the formation of Earth's core and the subsequent differentiation of the upper Earth into an enriched continental crust and a depleted mantle (which now melts and forms oceanic crust) will be described. Possible evidence for an early protocrust, supposedly subducted deep in Earth's mantle, will also be analyzed. Clearly, discussing all these topics related to the origin and development of the Earth is a large task for a small paper. However, this paper will hopefully at least provide a sense of how scientists are able to decipher the early history of our home planet and a general overview of Earth's origin and history.

Geology Word of the Week: V is for Vesicle (and Vug)

Vesicles in basalt, image courtesy of Ron Schott of the Geology Home Companion Blog.

def. Vesicle:
A small cavity in a volcanic rock that was formed by the expansion of a bubble of gas that was trapped inside the lava.

Munich in Pictures

Because of mechanical problems with an airplane, I took an unexpected route to South Africa. Travel is often this way; you have to be prepared for the unexpected. Often, the unexpected makes for the best travel stories. Now that I've recovered from jetlag and travel exhaustion, I have a good story... even if still I don't have my luggage four days after my arrival.

As a result of my changed travel schedule, I had a seven hour layover in beautiful Munich, Germany on April 21st.  Fortunately, the airport was not very busy, and I had enough time to make my way through customs, take the hour long train ride into the city, walk around the Marienplatz area for a few hours, and take the train back to the airport to check in for my flight to Cape Town. While I was having an early lunch in the Marienplatz, I was lucky enough to see the remarkable animation and music of the Rathaus-Glockenspiel.

Below are some pictures of my few hours in Munich. Click on any of the pictures to enlarge.

Statue man. If you come too close he threatens you with his sword!

Horse mural 1.

Geology Word of the Week: U is for Uraninite

Botryoidal uraninite. Image taken from wikipedia commons here.

def. Uraninite:
A uranium-rich mineral with the formula UO2 (uranium oxide). Often, part of the uraninite is oxidized with the formula UO3. Uraninite is the primary ore for uranium and can also be mined for other elements such as radium, thorium, and lead, which are decay products of radioactive uranium. Uraninite deposits are generally a dark steel black with a slight metallic luster. The shape of uraninite is typically botryoidal (looks like a bunch of grapes) or amorphous, but rare cubic and octahedral crystals can form in certain environments. Uraninite often forms when hydrothermal circulation picks up uranium from a uranium-rich rock (such as granite or syenite) and concentrates this uranium in a hydrothermal ore deposit. The primary reason that uraninite is mined is to provide fuel for nuclear power plants.

Off to South Africa...

In a few hours I begin about 30 hours of travel, starting with an 8am bus to the Boston Airport. I then take four flights: Boston-DC-Dakar-Johannesburg-Cape Town. I actually like traveling and airports and airplanes and such, but even for me this is a long, tiring trip.This is actually my sixth trip to South Africa. My fiance lives in South Africa (he's from Joburg originally), so we commute back-and-forth between Cape Cod and Cape Town as part of our very long distance relationship. I'm very excited to be traveling to Cape Town once again-- Cape Town is already a second home to me, and I plan to move there later this year. Traveling regularly on 24 to 36 hour trips to Cape Town, I can say this: those trips to Europe and cross-country are a breeze now.

In true busy grad student form, I spent the last few days reducing data and finishing up things in lab rather than preparing for my trip. So, I need to stay up a couple more hours to pack and wash dishes and such. Somehow in the midst of hours upon hours of data reduction, I never noticed the tornado that whipped through my apartment, scattering clothes and books and coffee cups everywhere. I need to try to reassemble my apartment into relative order before I leave. It's okay-- in my experience sleeping little the night before the trip can lead to some tolerable on-flight sleep. And at least on South African Airways the flight attendants are friendly, the food is edible, and you can drink as much beer and wine as you want.

I often work on my trips to South Africa, but I'm just bringing a few papers with me this time. I'm taking some much-needed vacation after 4 months of hard work in lab with very few days off and too much time spent indoors. When I return, I hope to be refreshed and ready to finish up the very last of the labwork for my PhD thesis.

Blogging may be a little light the next two weeks. I will post the Geology Word of the Week, and I will re-post an "Origin of the Earth" series which I wrote awhile back for Skepchick. When I return from my vacation, I promise to post some pictures from South Africa. I'll also finish up the Oklo natural nuclear reactor post and finish putting together the Lulu book of my interviews with my dad, a nuclear engineer, about the Fukushima Daiichi nuclear power plant disaster in Japan.

Okay, time to pack and wash dishes!

Lost Wonder of the World: Pink and White Travertine Terraces

Pink terraces, near Rotorua, New Zealand. Painting of the terraces done prior to 1886. Image taken from here.

Last week's geology word of the week was travertine. In response to the word of the week, a blog reader named Michael sent me a link to a wikipedia article about the spectacular-- but lost-- pink and white travertine terraces in New Zealand. I had never heard of these terraces before, but I clicked on the link to wikipedia and was immediately awestruck by paintings of these enormous travertine deposits. Intrigued, I began obsessively googling these travertines and found several more paintings and even a few grainy, late 1800s, black-and-white photographs. Often called the lost "Eighth Wonder of the World," these travertines attracted many European tourists back in the 1800s, no easy feat in an age when reaching New Zealand required a long ship voyage.

Good Hotplate

On Wednesday there was a bad hotplate incident that melted two of my samples. As scary and destructive (for my poor Oman rocks...) as this incident was, I'm happy to report that there is some good resulting. I've filed a full safety report, and with the help of a safety person I've been in touch with Thermo Scientific, the company that manufactured the defective hotplate. Maybe it's because Woods Hole Oceanographic Institution is a big client, but I've been very impressed at Thermo Scientific's response so far. We have a representative working with us on our case, and the company is launching an investigation of the incident to see if there is a problem with this model of hotplate. I really hope the company follows-through with the investigation. Thermo Scientific is also offering to buy me a new hotplate, though I told them I don't want another Cimarec hotplate since I don't trust this hotplate. I almost said, "I don't want your crappy unsafe hotplate," but I managed to put it a little more tactfully than that on the phone with the representative.

So, you might be wondering, what hotplate do I want? I want a PicoTrace safety hotplate, a geochemist's dream:

The dreamy PicoTrace hotplates. Image taken from here.

What a gorgeous hotplate.... separate temperature control outside of the corrosive environment, multiple safety features and temperature limits, a maximum temperature of 265 degrees C... I could go on and on about this dreamboat hotplate.

Alas, these beautiful hotplates start at about $3,000. I'm not sure if Thermo Fisher will spring for that, but perhaps they'll at least refund our money for the two hotplates that malfunctioned, and we can put that money towards the expensive hotplate. Also, I'm pretty sure the hotplate incident has convinced everyone involved in the lab re-design and money budgeting that it's worth it to pay for the $3,000 model hotplates. Yes, the PicoTrace hotplates are expensive, but they're worth it for safety.