Friday Jan. 12, 2018

Music from Brandi Carlile this morning: "Someday Never Comes" (2:44), "It's Over" (3:58), "Touching the Ground" (3:37), "Losing Heart" (3:35),
"The Joke" (4:56).

The Experiment #1 materials were checked out in class today.  Try to get started on the experiment as soon as you can.  A weekend is perfect, a 3-day weekend is even better.  The experiment can take a few days to run to completion.  You should check it every hour or two at the beginning, but it slows down as it goes and you may only need to check it once or twice during the day toward the end.  Once you've completed the experiment return the materials so that you can pick up a copy of the supplementary information handout.  It will help with the analysis of your data and will make materials available for someone else that wants to do the experiment.

Signup sheets for the remaining experiments and the Scientific and Books reports were also passed out in class.

The first of this semester's 1S1P topics are now online.  You can write reports on as many or as few of these as you wish.  I would suggest writing at least one report just to get some idea of how they are graded.


Dew point temperature continued

Here's a picture again of the cup of liquid nitrogen.  There are several things, both visible and invisible, to be aware of.






First of all the nitrogen.  We can see the liquid nitrogen.  Once the liquid has evaporated and turned to gas it is invisible.  You can't see the nitrogen gas.


Another invisible gas in air, water vapor, is coming into contact with the cold cup of liquid nitrogen.  The moist air cools enough that water vapor begins to condense and forms 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 are often only in the 20s. The 40 F soda bottle isn't able to get the air cold enough, the relative humidity stays below 100%,  and dew doesn't form on the bottle.

A little extra information added after class.
The air has been a little moister than normal following the rain earlier in the week and temperatures last night were a little cooler than normal.  It didn't quite cool to the dew point overnight but it came close.  Here are some data collected at the weather station set up near and on top of the PAS Bldg.


The low temperature overnight was about 41F, the dew point about 35 F.  80% relative humidity isn't high enough for fog to form but I could see that the air was noticeably hazy during my morning bike ride to campus.  

My car was covered with dew this morning much like the soda bottle in the picture above.  The car cooled to and maybe a little below 35 F overnight.

How to write a 1S1P report
Next we're going to cover a topic in class.  Then you'll have the option of writing a 1S1P about the same material.  We'll probably cover the subject 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 'll try to do in class).  That will give you an idea of the breadth of material that you'll need to fit into your one page report.  Then, if you choose to write a 1S1P report on this topic, read through the online reference material (the notes below are pretty nearly identical).  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

The information below wasn't presented very clearly in class, I apologize for that.  That's why we have online 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. 






Click here to learn more about Pluto's Gate to Hell.

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)  

Where did today's atmosphere come from?
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 NH3 reacted 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 argon found in air 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.




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 that 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.  When the comet had reached perihelion (the shortest distance between the comet and the sun), the Rosetta spacecraft 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 (you can read more about the composition of comets at https://www.universetoday.com/40692/what-are-comets-made-of/ ).  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.

The Lunar and Planetary Laboratory here at the U of A is one of the lead teams on the ORISIS - REx, mission which was launched in Fall 2016.  The goal of that mission is to send a spacecraft to Bennu, a near-earth asteroid, collect a sample of the asteroid and return it to earth.  If all goes according to plan the spacecraft will rendezvous with the asteroid in Aug. 2018 with sample acquisition occurring in July 2020.  The return capsule, containing the sample from the asteroid, should land in Utah on Sept. 24, 2023.

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 ) the stuff we need in order to survive.  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 break 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 atmospheric CO2 (photosynthesis is a "sink" for atmospheric CO2 , it removes CO2 from the air). Carbon dioxide will probably be 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.

This is as far as we got in class today but we did cover the main points that should go into a 1S1P report on the Origin and Evolution of the Earth's atmosphere.

 Here's a cleaner version of the outline of what we covered today:



Add a few details and some explanation to this outline, turn it all into sentences and paragraphs and you'll have a pretty good report.

We'll cover the remaining material at the start of class next Wednesday.

 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 is what 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.   They're evidence of an early form of life on earth being 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 (some forms of blue green algae may be toxic).  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 pictures of the two 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).