Despite taking over 23,000 breaths
per day, you probably don’t often wonder where the oxygen necessary for your
survival comes from. In fact, this
question is still being asked by scientists and many are currently working to better
understand how and when oxygen arose in our atmosphere. The term Great
Oxidation Event, or GOE, is used to describe the point (or period) when the
Earth’s atmosphere began to accumulate oxygen and is thought to have
occurred about halfway through Earth’s lifetime, around 2.4 Ga (Ga = billion years ago).
One of the methods used to
constrain the timing of the GOE is to track where the element molybdenum (Mo) is found
throughout Earth history. While uncommon, Mo is produced in the igneous rocks
in the Earth’s crust as magmas rise towards the surface and is often associated with hydrothermal alteration of igneous rocks. It is thought to
concentrate in sulfides, as it has been shown to have an affinity to the element sulfur. One of the most common sulfides in the crust is pyrite, FeS2,
as pictured below. The uniqueness of Mo lies in its sensitivity to oxygen –
when exposed to oxygen in the atmosphere, the soluble Mo6+ ion will weather out
of pyrite in the crust and will be carried to rivers and oceans through erosional
processes.
Geologists
measure Mo concentrations in shales throughout time to determine when Mo began to appear in ocean sediments, an analog to when free oxygen accumulated in the
atmosphere. While this method has timed
the GOE in concordance with other approaches, the use of Mo as an oxygen proxy is a method
that is still being refined.
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Really good intro to relate the accumulation of oxygen in the atmosphere to something as simple as breathing. It is an excellent opening to introduce the GOE.
ReplyDeleteYou have some pretty tough concepts to get across to a general audience with a discussion of Mo enrichment, and did a good job overall. I especially like the sentence about why geologists use Mo concentrations (paragraph 3) . Maybe it would be better a little earlier in the blog, though, as a transition in paragraph 2.
There are still some terms that could be defined/explained a little, or replaced with simpler language--what is a sulfide? exsolved chalcopyrite? hydrothermal alteration? what does 'Mo+6' mean?
The photomicrograph is an awesome image, and maybe it could be closer to the text in which it is referenced instead of at the bottom.
Last tiny thing--typo in the opening sentence ('wander' instead of 'wonder').
Tom
The "wander" is embarrassing... oops. Thanks for the comments! Very helpful
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ReplyDeleteThis is a pretty good simplification for someone already familiar with geology. And it's nice to see what your research is covering, really cool stuff. It's just that my grandparents would be scratching there heads at about the 2nd or 3rd sentence.
ReplyDeleteExamples of more simplification:
Why use 'atmosphere,' instead of just 'the earth.' Most lay people I know don't realize that the atmosphere is also right around us, but instead as 'that place in the sky that planes go.'
"point (or period)" how about simply "time"
Why even use 'Ga,' or 'Ma?' Why not spell out 'billion and million years exclusively?
And the figure is completely useless to a lay person. Heck, I don't even understand it. Everything before 500 Ma looks the same to me...
I think "earth" would be just as confusing as "atmosphere". Maybe just briefly explaining what is meant by atmosphere would help. Many people think atmosphere means ozone layer or that boundary spacecraft "hit/scrape" in movies, so I agree with what you are saying, but there is a limit to how much you can dumb something down in finite space, and still retain the correct meaning.
DeleteThis helped me understand Mo in the crust a lot better but I agree with others on some of the jargon. Also, a little picky but the two captions for figure 1 are a little confusing
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ReplyDeleteThis is a great start to a difficult concept, and the air we breath introduction is wonderful. You need to simplify some of the terms to reach a general audience, and not rely simply on geological terms. The figure captions need to be as general and accessible to the audience as the main text, which could be a bit longer to improve understanding and provide insight about the processes that could be occurring. Mo has an important biological function as well for photoautotrophs, so you might weave an evolutionary idea into the story.
ReplyDeleteIt is really helpful for me to learn how Mo is studied in GOE. It took me a while to understand figure 1, as well as some word, such as pyrite, hydrothermal alteration. Some of the word are really basic geology, but I doubt if all the readers will be able to follow.
ReplyDeleteI liked it. So, where did the O come from? Minerals with O in them? Plant life in the ocean? These aren't just suggestions of things to talk explain, I actually don't know these answers( I have forgotten them long ago at least). I am guessing that most people would wonder this too then, who do not know a lot about early earth evolution.
ReplyDeleteAs a commoner, ive always assumed we got the O we breathe from plants. You use words like soluble and hydrothermal, my grandma would have no clue what that means. Also the figure caption for the first figure is super dense and uses terms like "non-euxinic"...I don't even know what that means. Maybe drop it and write your own. Otherwise...cool topic!
ReplyDeleteAs a commoner, ive always assumed we got the O we breathe from plants. You use words like soluble and hydrothermal, my grandma would have no clue what that means. Also the figure caption for the first figure is super dense and uses terms like "non-euxinic"...I don't even know what that means. Maybe drop it and write your own. Otherwise...cool topic!
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