Cuesta College, San Luis Obispo, CA
Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.
(The following question was asked following the lecture on star formation, evolution, novae, type Ia supernovae, and type II supernovae, but before the lecture on planetary formation in nebular disks.)
_________ produced the gold and silver in Earth's crust. (Graded for completion.)
(A) Nucleosynthesis in the first few minutes after the start of the big bang.
(B) Fusion reactions in the sun's core.
(C) Fusion reactions in the core of another main-sequence star.
(D) Nuclear reactions during a type Ia or type II supernovae explosion.
(E) (More than one of the above choices.)
(F) (None of the above choices.)
(G) (I'm lost, and don't know how to answer this.)
Student responses
Sections 70158, 70160
(A) : 9 students
(B) : 10 students
(C) : 6 students
(D) : 16 students
(E) : 10 students
(F) : 4 students
(G) : 9 students
Correct answer: (D)
Stars fuse hydrogen into heavier elements in their cores. Medium-mass stars have carbon as their end product of fusion; while massive stars have iron has their end product. However, type Ia supernova of these medium-mass stars as white dwarfs would result in heavier elements than carbon being made, and especially the type II supernova of massive stars would result in much heavier elements than iron, such as gold and silver. These heavy elements from a previous generation star's remnants would then be incorporated into the formation of Earth in the early solar system.
(Students were then prompted to fill in a text box online to justify their answer.)
Briefly explain your answer for the above question (what produced the gold and silver in Earth's crust). (Graded for completion.)
The following are all of the student responses to this question, verbatim and unedited.
"It all started a long time ago.... It was a simpler time back then-- the air seemed a little cleaner, the days a little brighter. All was well and all were happy... Then one fatefull day, all of that changed. The people of this careless little planet were doomed.. for little did they know an evil was growing, the likes of which would never be met in this storyteller's lifetime. And it all started on a little island in the pacific, on an average day, in an average house, a child born to two average people. But this was no average child. He didn't play in the sandbox, he measured the amount of meteorite particals in the sand. And he didn't watch tv, he watched the sky, plotting; biding his time till be would one day conquor all!!! Coming this summer.
One man. One lecture hall. Highlander IV- the wrath of P-Dog!!! Did ya enjoy the plug for my new movie?"
"Gold and silver in the Earth's crust is produced by the fusion reactions in the core of another main-sequence star and the fusion reactions in the sun's core."
"the reaction in the suns core produced the gold and silver"
"idk i guess"
"guessed"
"yep"
"Atoms heavier than iron were created during rapid nuclear reactions during supernova explosions, gold and silver being two of them."
"supernova's release neutrons and they have no repulsion"
"Stars fuse elements up to iron, heavier elements are formed during supernovae."
"how can exploisions from other stars add gold and silver to the Earth's crust? doesn't seem right"
"The fusion of two nuclei with lower mass than iron generally releases energy while the fusion of nuclei heavier than iron absorbs energy; vice-versa for the reverse process, nuclear fission"
"Heavy metals were created at the big bang"
"I think i read it in the book."
"Both fusion and nuclear reactions were involved."
"The heavier elements were created in the suns core through fusion. When the solar system was formed these elements attached to the earth."
"through all the tempetures in the the earth heips create it as well"
"Lots of heat and fusion"
"The explosion created heavy metals like gold and silver which became the basis of earth's crust."
"i put i'm lost....because i'm lost"
"Gold created as byproduct of supernovae, flung through space to other developing stars/planets."
"the gold and silver within minutes nucleosynthesis occurs"
"I used deductive reasoning."
"normal matter and particles of antimatter."
"just gussing"
"i guessed"
"fusionism centralates the central nalgistic and forms collaberation in the drantaieeasm which travels from the core fusion to the crust and disscombobulates the balance of elements a and b...(a being gold and b being silver) thus proving why i chose my answer"
"The elements are scattered out after a supernova."
"I'm lost, and don't know how to answer this."
"I looked it up"
"im not sure.."
"Star starts to collapse. The collapse can trigger a supernova explosion which will seed the interstellar medium and the dust clouds with the elements created during its lifetime. And the intense heat and pressure of the explosion can create elements heavier than iron (gold, silver, uranium, lead, etc.) and those are also expelled into the interstellar medium."
"As usual I have no idea."
"i really dont know"
"Not too sure!"
"dont knwo"
"I don't know, I figured that a supernovae could create that."
"As the sun gets older the heavier the elements the sun will start to fuse and when it explodes all of these elements are released and created all the elements of the periodic table"
"I'm not sure it makes since to me that it would happen in the core of something."
"i just guessed"
"Because boom = money"
"heavier elements than hydrogen or helium form in the cores of other stars, so one of these stars may have gone through a supernova. The intense heat make the elements heavier than iron and the explosion shoots the material out and maybe creating the earth."
"Well I selected it because, I was lost. And didn't know how to answer it."
"I am not really sure."
"kjdakd;sa"
"dont got a clue"
"I feel it would take a combination of things, to create both gold and silver as they are two different things."
"i guessed? didnt want to cheat and look at text book"
"I don't know! Me can't find it in book! If you give me full point I'll be your best friend. jk
it was the supernovea cuz it was the only time to fuse the lighter and heavier elements"
"Fusion reactions in the core of any star."
"actually to be quite accurate i'm not ready to give a definitive answer. were it "____ is a widely accepted theory for why..." i would say D because it is widely accepted."
"idk"
"I don't know"
"I can't find the answer!"
"I don't know if thats the answer, but I think I remember hearing that."
"Only nuclear reactions from a type Ia or type II supernovae explosion can create enough energy to fuse lighter elements into elements as massive as gold and silver."
"i dont really know the answer to the question"
"i'm not sure how to answer this"
"Help?"
"...???"
"The earth's crust is so complex...i cant exactly remember what the reading said caused it...
because nuclear reactions create gold and silver."
"umm well the gold and silver were made from fusion but it couldn't have been from the sun because the sun is still fusing its hydrogen together."
"Not sure, figured gold could be created from fusion reations from either"
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