Thu., Aug. 28 notes

Thursday Aug. 28, 2014

A nice selection of music from Sergio Mendoza y La Orkesta recorded in Austin, TX, this past summer during the SXSW festival. They're a local group and will be playing downtown this coming Sunday night, I believe, as part of the HOCO Fest.

Experiment #1 materials checkout
About 45 sets of Experiment #1 materials were checked out before class today. Those of you that have materials will eventually find your name on the Expt. #1 signup list. Even though your report isn't due until Sep. 23, the experiment can take several days, maybe even a week, to run to completion so don't wait too long to get it started; this weekend would be a perfect time. You may need to check the experiment fairly frequently at the beginning (every hour or two). It slows down somewhat as it progresses and eventually you will only need to look at it once or twice a day. You'll find more information about the experiment here.

Once you have collected your data, return your materials and pick up the supplementary information handout. Try to do this before the experiment report is due because the handout will help with the analysis portion of your report. It will also make materials available for someone else that wants to do the experiment. Your name should turn this rust color on the signup list when you have returned your materials.

Signup sheets for the remaining experiments were circulated in class. If you didn't get a chance to signup don't worry, I'll bring the lists to class again next week. And remember you only need to do one of the experiments. You can check on the appropriate list to see if your name is there (it will take a few days to enter all the names)

Storm photographs

Close to an inch of rain fell on campus during Tuesday afternoon's storm. The Arizona Daily Star has some pretty good photographs of flooded streets.

And speaking of photography you really should spend a few minutes looking at some of Mike Olbinski's Storm Photography. He really has some amazing pictures.

Here's the list of the 5 most abundant gases in our atmosphere again together with what we learned about them in class on Tuesday.

We'll be learning more about some of these gases today and will be filling in the open circles with new information.

The earth's original atmosphere and the origin(s) of our present atmosphere

Our present day atmosphere is very different from the earth's original atmosphere which was mostly hydrogen and helium with lesser amounts of ammonia and methane.

I'm not sure I mentioned how/why the earth lost its first atmosphere. It probably either escaped (the earth was hot and light weight gases like hydrogen and helium were moving around with enough speed that they could overcome the pull of the earth's gravity) and was swept into space by the solar wind (click on the link if you are interested in learning more about the solar wind, otherwise don't worry about it).

With the important exception of oxygen (and argon), most of our present atmosphere is though to have come from volcanic eruptions. In addition to ash, volcanic eruptions send a lot of water vapor, carbon dioxide, and sulfur dioxide into the atmosphere. Carbon dioxide and water vapor are two of the main gases in our present atmosphere.

Volcanoes also emit lots of other gases, many of them are poisonous. Some of them are shown on the right side of the figure (I found the gases in the "also" list mentioned in a lot of online sources, the gases in the "perhaps" list were mentioned less frequently).

As the earth began to cool the water vapor condensed and began to create and fill oceans. Carbon dioxide dissolved in the oceans and was slowly turned into rock. Smaller amounts of nitrogen ( N₂ ) are also emitted by volcanoes.. Because nitrogen is relatively nonreactive it remained in the air and its concentration was able to built up over time.

The photo above shows the Eyjafjallajokull volcano in Iceland photographed on Apr. 17, 2010 (image source)

Here are some additional pictures of the Eyjafjallajökull volcano. It caused severe disruption of airline travel between the US and Europe. Here's another set of photos also from the Boston Globe.


Water has filled the Askja volcano caldera forming Oskjuvatn Lake. The lake covers 12 sq. kilometers and is 220 m deep. The small lake in the foreground is Viti lake.	Closeup of Viti geothermal lake. Source of both images

There has been an increase in earthquake activity around the Bardarbunga volcano in Iceland (which lies underneath a glacier) and there is concern that magma might move from Bardarbunga into the nearby Askja volcano (shown above) and cause it to erupt (see this Aug. 27 reference for more information).

Friday Aug 29 update
We didn't have to wait very long to hear about activity coming from Iceland. A small fissure eruption was observed overnight at the Bardarbunga volcano.

Midnight fissure eruption at the Bardarbunga volcano in Iceland (source of this image)

A much bigger eruption at the Tavurvur volcano on New Britain Island in Papua New Guinea also occurred overnight sending ash and dust up to 60,000 feet.

The Tavurvur eruption (source of this photograph)

Tavurvur is a pretty active volcano. The town of Rabaul is located nearby. I spend some time there as part of a field experiment in 1992. The same volcano erupted in 1994 and buried Rabaul.

Where did the oxygen in our atmosphere come from?
Volcanoes didn't add any of the oxygen that is in the atmosphere. Where did that come from? There are a couple of answers to that question.

1st source of atmospheric oxygen

The oxygen is thought to have come from photo-dissociation of water vapor and carbon dioxide by ultraviolet (UV) light (the high energy UV light is able to split the H₂0 and CO₂ molecules into pieces). The O and OH then react to form O₂ and H.

By the way I don't expect you to remember the chemical formulas in the example above. It's often easier and clearer to show what is happening in a chemical formula than to write it out in words. If I were to write the equations down, however, you should be able to interpret them. Ultraviolet is a dangerous, high energy, potentially deadly form of light and it's probably also good to remember that ultraviolet light is capable of breaking molecules apart.

Once molecular oxygen (O₂) begins to accumulate in the air UV light can split it apart to make atomic oxygen (O). The atoms of oxygen can react with molecular oxygen to form ozone (O₃).

Ozone in the atmosphere began to absorb the dangerous and deadly forms ultraviolet light and life forms could then begin to safely move from the oceans onto land (prior to the buildup of ozone, the ocean water offered protection from UV light. A molecule of O₃ absorbs some UV preventing it from reaching the ground.

O₃+ UV light ---> O₂ + O

You might think the O₂ and O would recombine, but they usually go flying off in different directions. This ozone destruction reaction wasn't shown in class.

2nd and most important source of atmospheric oxygen.
Photosynthesis is now the main source of atmospheric oxygen.

Photosynthesis in its most basic form is shown in the chemical equation above. Plants need water, carbon dioxide, and sunlight in order to grow. They can turn can turn H₂0 and CO₂ into plant material. Photosynthesis releases oxygen as a by product.

Combustion is really just the opposite of photosynthesis and is shown below.

We burn fossil fuels (dead but undecayed plant material) to generate energy. Water vapor and carbon dioxide are by products. Combustion is a source of CO₂. We'll see these two equations again when we study the greenhouse effect (CO₂is a greenhouse gas ) and global warming.

And a detail that I didn't mentioned in class (and something you probably don't need to remember). The argon we have in the atmosphere apparently comes from the radioactive decay of potassium in the ground. Three isotopes of potassium occur naturally: potassium-39 and potassium-41 are stable, potassium-40 is radioactive and is the source of the argon in the atmosphere.

Stromatolites, banded iron, red beds - geological evidence of oxygen on earth

The following figure is the first page in the packet of photocopied ClassNotes.

This somewhat confusing figure shows some of the important events in the history of the earth and evolution of the atmosphere. There were 5 main points I wanted you to take from this figure, and really 1-3 are the most important.

First, Point 1: the earth is thought to be between 4.5 and 4.6 billion years old. If you want to remember the earth is a few billion years old that is probably close enough. Something I didn't mention in class, it's in small type above. The formation of a molten iron core was important because it gave the earth a magnetic field. The magnetic field deflects the solar wind and keeps the solar wind from blowing away our present day atmosphere.

Stromatolites (Point 2) are column-shaped structures made up of layers of sedimentary rock, that are created by microorganisms living at the top of the stromatolite (I've never actually seen a stromatolite, so this is all based on photographs and written descriptions). Fossils of the very small microbes (cyanobacteria = blue green algae) have been found in stromatolites as old as 2.7 B years and are some of the earliest records of life on earth. Much older (3.5 to 3.8 B years old) stromatolites presumably also produced by microbes, but without microbe fossils, have also been found.

Blue green algae grows at the top of the column, under water but near the ocean surface where it can absorb sunlight. As sediments begin to settle and accumulate on top of the algae they start to block the sunlight. The cyanobacteria would then move to the top of this sediment layer and the process would repeat itself. In this way the stromatolite column would grow layer by layer over time. Now, this isn't a geology class; we're learning about stromatolites because the cyanobacteria on them were a very early form of life on the earth and were able to produce oxygen using photosynthesis.

Living stromatolites are found in a few locations today.The two pictures above are from Lake Thetis (left) and Shark Bay (right) in Western Australia (the two photos above and the photograph below come from this source). The picture was probably taken at low tide, the stromatolites would normally be covered with ocean water. It doesn't look like a good place to go swimming, I would expect the top surfaces of these stromatolites to be slimy.

Living stromatolites at Highborne Cay in the Bahamas.

Point 3 refers to the banded iron formation, a type of rock formation. These rocks are 3 billion years old (maybe older) and are evidence of oxygen being produced in the earth's oceans. Here are a couple of pictures of samples of banded iron formation rock that I passed around in class (thanks for being careful with them and not stealing them). Thanks also for being careful with the glass graduated cylinders. I don't believe any were broken in either of the sections.

The main thing to notice are the alternating bands of red and black. The next paragraph and figure explain how these formed.

Rain would first of all wash iron ions from the earth's land surface into the ocean (at a time before there was any oxygen in the atmosphere). Oxygen from the cyanobacteria living in the ocean water reacted with the dissolved iron (the iron ions) to form hematite or magnetite. These two minerals precipitated out of the water to form a layer on the sea bed. This is what produced the black layers.

Periodically the oxygen production would decrease or stop (rising oxygen levels might have killed the cyanobacteria or seasonal changes in incoming sunlight might have slowed the photosynthesis). During these times of low oxygen concentration, red layers of jasper would form on the ocean bottom. The jasper doesn't contain as much iron.

Eventually the cyanobacteria would recover, begin producing oxygen again, and a new layer of hematite or magnetite would form. The rocks that resulted, containing alternating layers of black hematite or magnetite and red layers of jasper are known as the banded iron formation. In addition to the red and black layers, you see yellow layers made of fibers of quartz in the samples passed around class. The rocks are fairly heavy because they contain a lot of iron, but the most impressive thing about them in my opinion is their age - they are a few billion years old!

Eventually the oxygen in the oceans reacted with and used up all of the iron ions. Oxygen was then free to move from the ocean into the atmosphere. Once in the air, the oxygen could react with iron in sediments on the earth's surface. This produced red colored (rust colored) sedimentary rock. These are called "Red Beds" (Point 4). None of these so-called red beds are older than about 2 B years old. Thus it appears that a real buildup up of oxygen in the atmosphere began around 2 B years ago.

Red State Park near Sedona Arizona. An example of "red beds" that formed during the Permian period 250-300 million years ago.

Oxygen concentrations reached levels that are about the same as today around 500 to 600 million years ago (Point 5 in the figure).

Here's our earlier list with some additional details added

We had time to add to the list also.
Trace gases in air - pollutants and greenhouse gases

Carbon monoxide, nitric oxide, nitrogen dioxide, ozone, and sulfur dioxide are some of the major air pollutants. We'll cover 3 of these in more detail next week.

Water vapor, carbon dioxide, methane, nitrous oxide (N₂O = laughing gas), chlorofluorocarbons, and ozone are all greenhouse gases. Increasing atmospheric concentrations of these gases are responsible for the current concern over climate change and global warming. We'll discuss this topic and learn more about how the greenhouse effect actually works later in the course.

Ozone has sort of a Dr. Jeckyl and Mr. Hyde personality

(i) Ozone in the stratosphere (a layer of the atmosphere between about 10 and 50 km altitude) is beneficial because it absorbs dangerous high energy ultraviolet (UV) light coming from the sun. Without the protection of the ozone layer, life as we know it would not exist on the surface of the earth. It was only after ozone started to buildup in the atmosphere that life could move from the oceans onto land. Chlorofluorocarbons are of concern in the atmosphere because they destroy stratospheric ozone.

(ii) In the troposphere (the bottom 10 kilometers or so of the atmosphere and where we live) ozone is a pollutant and is one of the main ingredients in photochemical smog.

(iii) Ozone is also a greenhouse gas.

Finally, I wasn't being entirely honest when I said that gases are invisible. Some gases can be seen, here are some examples. I would like to bring some actual samples to class, but some are very toxic and require careful handling.


Bromine in both liquid and gaseous phases. Bromine and mercury are the only two elements that exist as liquids at room temperature. The bromine is in a sealed glass ampoule inside an acrylic cube. Bromine could be safely brought to class in a container like this. This photo was taken by Alchemist-hp and was Picture of the Day on the English Wikipedia on Oct. 29, 2010.	Chlorine (Cl₂) I found this image here	Iodine Also an element that is normally found in solid form. The solid sublimates, i.e. it changes directly from solid to gas (you would probably need to heat the solid iodine to produce gas as dense as seen in the picture above). source of this image	Nitrogen dioxide (NO₂) An important pollutant. source of this image