Fri., Jan. 15 notes

Friday Jan. 15, 2016

Music to check experiment materials by: Mona's Hot Four: "Temptation Rag" (3:51), "My Blue Heaven" (5:14), "Comes Love with Rachael Price" (9:20), "Tuesdays at Mona's (Documentary)" (19:11)

Close to 40 sets of Experiment #1 materials were distributed in class today. A 3-day weekend is the perfect time to start (and most likely finish) this experiment. Experiment materials and instructions and a data collection sheet are inside the cylinder. You should eventually find your name and the number on the cylinder you checked out on the Report Signup List for Experiment #1. Some additional information about the experiment can also be found there.

Something I forgot to mention in class: Try to finish the experiment well before the due date. That way you can return the materials and pick up a supplementary information sheet that will help with the analysis portion of your report. Returning the materials early also makes them available for someone else that wants to do the experiment.

Signup sheets for the other experiments, the scientific paper and book reports were passed around class. Those names will also make their way to the appropriate signup sheets. If you didn't have a chance to signup you can do so next week. And you're not locked into what you chose to do today.

Three 1S1P report topics are now available for you consideration. If you were to turn reports on all 3 topics and earned average grades on each, you'd have 22 pts and would be half way to the 45 pts by the end of the semester goal.

An Optional (Extra Credit) Assignment is also available. If you make an honest attempt to answer all the questions and have the assignment complete before coming to class on the due date (next Friday, Jan. 22) you will receive full credit on the assignment (even if you don't answer the questions correctly).

We had a couple of topics from Wednesday to finish up.

Tucson's summer monsoon

Tucson usually gets between 11 and 12 inches of rain per year. About half of that comes during the summer monsoon, i.e. the summer thunderstorm season. Many people mistakenly think the term monsoon is just another word for thunderstorm.

For most of the year in SE Arizona winds come from the west and are relatively dry. For 2 or 3 months every summer the winds switch direction and start to blow from the east and southeast. This air is much moister. The combination of moist air and summertime heating make it much easier for thunderstorms to form.

Tucson residents generally look forward to the start of the summer thunderstorm season because the rain brings some relief from the hot dry weather of May and June. Recall that the dew point temperature gives you an idea of how much water vapor is in the air. The switch in wind direction and the arrival of moister air is often indicated by a fairly abrupt increase in the daily average dew point temperature.

The figures below are from the Tucson National Weather Service Office and shows a plot of average daily dew point temperatures (red curve) for June - September 2015.

Traditionally the summer monsoon would start when the daily average dew point remained at or above 54 F green line for 3 days in a row. Using the chart above we can see that occurs on July 9 on average. The average dew point temperature drops below 54 F around Sept. 11. Using this traditional definition, the summer monsoon season normally extends from July 9 through 11.

In any given year the measured daily dew point values can depart appreciably from average. The four figures below show measured daily dew point values from summer 2015. Measured values are in blue. The red line again shows average daily dew point values and the green line is 54 F.


Measured and average dew points in Tucson for June and July 2015.

The average dew point value reached 54 F on June 25 in 2015. That was an earlier than normal start to the summer monsoon. Measured dew points for August and September are shown below.


Measured and average dew points in Tucson for August and September 2015.

The measured dew point fell below and remained below 54 F on Sept. 25 in 2015.

That's how meteorologists used to identify the start and end of the summer monsoon. Beginning in 2008 a monsoon of fixed duration, June 15 through Sept. 30, began being used regardless of what the actual dew point values were.

Dew point temperature continued

Now let's go back to the cup of liquid nitrogen

Two things are going on here.
First, the liquid nitrogen is evaporating. We can see the liquid nitrogen, but the nitrogen gas is invisible.

Second invisible water vapor (gas) is coming into contact with the cold cup of liquid nitrogen. The moist air cools enough that water vapor begins to condense and form a forming a cloud consisting of very small drops of liquid water and small crystals of ice. The cloud is visible.

We're seeing a demonstration of the dew point's "second job."

If you cool air next to the ground to its dew point, water vapor will condense and coat the ground (or your car) with water. The ground will be covered with dew. If a little thicker layer of air is cooled fog will form. A soda bottle in the refrigerator cools to about 40 F. In the summer in Tucson the dew point will be in the 50s or 60s. The soda bottle is cold enough that when removed from the refrigerator it can cool the air to and below its dew point and water vapor will condense onto the side of the bottle as shown below. (source of the photo)

Except for the summer, the air is usually too dry in Tucson for this to happen. Dew points might only be in the 20s. The 40 F soda bottle isn't able to get the air cold enough and dew doesn't form on the bottle.

I'm going to try something for the first time this semester. I'm going to cover a topic in class and also make it a 1S1P topic. We'll probably cover the material in class a little more quickly than I normally would. Concentrate on how the material is organized. Don't worry too much about all the details. You might create an outline (that's what I tried to do in class). That will give you an idea of the breadth of material that you'll need to fit into your report. Then, if you choose to write a 1S1P report on this topic, work back through the reference the material. Focus on understanding some of the details at that point so that you can add them to your report.

The earth's original atmosphere and our present day atmosphere

I've stuck what I think is a reasonable outline of this topic at the very end of today's notes.

Our present day atmosphere (shown below at left) is very different from the earth's original atmosphere (at right below) which was mostly hydrogen and helium with lesser amounts of ammonia and methane.

The early atmosphere either escaped into space (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) or was swept into space by the solar wind.

The earth's magnetic field protects our present atmosphere from the solar wind. Mars does not have a magnetic field and the solar wind is stripping away its thin atmosphere. The MAVEN space mission to Mars has been measuring how quickly this is occurring. I'm mentioning Mars mostly so that I can insert the picture below which is an artist's impression of the solar wind blowing away the atmosphere of Mars (source of this image, the article also includes a solar wind animation and more information about the MAVEN mission).

An artist's impression of the solar wind blowing away the atmosphere of Mars (source of this image)

Volcanoes
With the important exception of oxygen (and argon perhaps), most of our present atmosphere is though to have come from volcanic eruptions. In addition to ash, volcanoes send a lot of water vapor, carbon dioxide, and sulfur dioxide into the atmosphere. Carbon dioxide and water vapor are two of the 5 main gases in our present atmosphere.

Volcanoes also emit lots of other gases, many of them are very poisonous. Some of them are shown on the right side of the figure. The gases in the "also" list were mentioned in a lot of online sources, the gases in the "perhaps" list were mentioned less frequently. The relative amounts of these "also" and "perhaps" gases seems to depend a lot on volcano type.

As the earth began to cool the water vapor condensed and began to create and fill the earth's oceans. Carbon dioxide dissolved in the oceans and was slowly turned into rock. Nitrogen containing compounds like ammonia ( NH₃ ) and molecular nitrogen ( N₂ ) are also emitted by volcanoes. I'm guessing that the nitrogen in NH₃reacted with other gases to produce N₂. Molecular nitrogen is pretty nonreactive so once in the air 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 which you should really have a look at.
Eyjafjallajökull caused severe disruption of airline travel between the US and Europe.
Here's another set of photos also from the Boston Globe)

Comets

This photograph is a mosaic of 4 images taken over a roughly 20 minute period from an altitude of 28.6 km (17.8 miles). Photo credit: "Comet 67P on 19 September 2014 NavCam mosaic" by ESA/Rosetta/NAVCAM found a Wikipedia article on the Rosetta mission.

A mosaic of the first two images showing the Philae lander on the comet's surface. photo credit: ESA/Rosetta/Philae/CIVA photo source

These photographs of Comet 67P/Churyumov-Gerasimenko taken by the European Space Agency Rosetta spacecraft. The spacecraft was launched on March 2, 2004 and went into orbit around the comet on August 6, 2014. On November 12, the Rosetta spacecraft deployed the Philae lander which successfully landed on the surface of the comet and operated for a brief time. How amazing is that. The lander was not able to fully deploy its solar panels and used up its battery power and went into "sleep" mode after about 60 hours of operation. In June 2015 the comet had moved into a sunnier part of its orbit and the lander began sending data again. The comet has just reached perihelion (shortest distance between the comet and the sun). The Rosetta spacecraft has photographed material being ejected from the comet (you'll find a nice animation here).

I've included this photograph of a comet because some researchers don't believe that volcanic activity alone would have been able to account for all the water that is on the earth (oceans cover about 2/3rds of the earth's surface). They believe that comets and asteroids colliding with the earth may have brought significant amounts of water. The Rosetta spacecraft has determined that the water on this particular comet differs from the composition of the water in the earth's oceans (this reference reports "The ratio of deuterium to hydrogen in the water from the comet was determined to be three times that found for terrestrial water." Deuterium is a hydrogen isotope, the nucleus contains one proton and one neutron; the nucleus of "normal" hydrogen just contains a proton) This suggests that comets like 67P anyways were probably not an important source of the earth's water.

Where did the oxygen in our atmosphere come from?

Oxygen is in H₂O, CO₂, and SO₂ (and many of the other gases emitted by volcanoes) but volcanoes don't emit molecular oxygen ( O₂ ) like is found in air air. Where did the O₂ come from? There are a couple of answers to that question.

1. Photodissociation

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). Two of the pieces, 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.

Production and destruction of ozone

Once molecular oxygen (O₂) begins to accumulate in the air ultraviolet (UV) light in sunlight can split the O₂ apart to make atomic oxygen (O). The atoms of oxygen can react with molecular oxygen to form ozone (O₃). This is shown in the top part of the figure below.

This is an important step. Ozone in the upper atmosphere began to absorb the dangerous and deadly forms ultraviolet light and prevented it from reaching the surface. 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). The absorption of UV light by ozone is shown at the bottom of the figure above and repeated below

O₃+ UV light ---> O₂ + O

You might think the two "pieces" O₂ and O would recombine. But if you picture hitting something with a hammer and breaking it, the pieces usually fly off in different directions. That's essentially what happens with the O and O₂ .

2. Photosynthesis

Once plant life had developed sufficiently and once plants had moved from the oceans onto land, photosynthesis became 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 essentially 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 (photosynthesis is a "sink" for atmospheric CO₂ , it removes CO₂ from the air). Carbon dioxide is the subject of an upcoming 1S1P assignment and we'll see these two equations again there and when we study the greenhouse effect and global warming.

This is also in its most basic form what we (people) are doing. We eat food (fuel) and breathe in oxygen. The food is "burned" to generate the energy needed to keep our bodies functioning, we exhale carbon dioxide.

Here's a detail that I often forget to mention when this material is covered 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.

You could probably end your 1S1P report at this point (depending on how much detail you add). Or you could add some of what follows to your report.

This was also about where we were starting to run out of time in class. We covered a portion of what follows though in a little bit too much of a hurry and it probably wasn't very clear (sorry about that).

Geological evidence of early oxygen in the earth's oceans and atmosphere

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 are 5 main points I want you to take from this figure. Points 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. A relatively minor point shown in the figure: the formation of the earth's molten iron core was important because it gave the earth a magnetic field. The magnetic field deflects the solar wind and prevents the solar wind from blowing away our present day atmosphere.

Stromatolites (Point 2) are geological features, column-shaped structures made up of layers of sedimentary rock, that are created by microorganisms living at the top of the stromatolite (I'm not a geologist and 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 year old) stromatolites presumably also produced by microbes, but without microbe fossils, have also been found.

Stromatolites

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.

You might be wondering why we are learning about stromatolites. It's because the cyanobacteria on them 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. Hamelin Pool in Western Australia is a World Heritage Area, the stromatolites there are the oldest and largest living fossils on earth (see this source for more information)

Living stromatolites at Highborne Cay in the Bahamas.

Banded iron formation
Point 3 refers to the banded iron formation, a type of rock formation. These rocks are 2 - 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.

The main thing to notice are the alternating bands of red and black. The rocks are also relatively heavy because they contain a lot of iron. The next paragraph and figure explain how these rocks formed.

Rain would first of all wash iron ions from the earth's land surface into the ocean (this was at a time before there was any oxygen in the atmosphere). Once in the ocean, the iron ions reacted with oxygen from the cyanobacteria living in the ocean water 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, would 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.

Red beds
Eventually the oxygen in the oceans reacted with all of the iron ions in the water. Oxygen was then free to diffuse 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 Rock 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 a cleaner version of the outline of this topic that we were working on in class.

Add a few details and some explanation and turn all this information into sentences. It really helps, also, to split even a 1 page report into a few shorter paragraphs with one main idea per paragraph.