A very unscientific explanation of how shells are formed

Ever since I’ve started working for this MOOC, I can’t help but see it everywhere. Walking around the Tate Britain this past weekend I came across these six shelfs of shells – carbon cycle anyone?

In between some funny letters and a video of a man without pants, Damien Hirst – Forms Without Life (1991) at the Tate Britain. Last week’s reflection finished with this question: How do certain organisms form shells by grabbing carbon from the ocean and layering it onto their backs?
This curiosity comes from previous weeks when it was mentioned that certain organisms make skeletons and shells that they use during their lives and when they die *sad face*, these structures sink to the deep ocean floor and with time and pressure become part of what today we buurrrrrn relentlessly: fossil fuels.
Well, the process by which organisms form minerals is called biomineralization. If you are familiar with the specialised language of this discipline, then go ahead and read this paper and skip to the last bit of this post (Questions for upcoming weeks and other stuff),  if you’re not and you want to get a brief overview, here is my digest about how this magical (biochemical) process works.
There are two types of biomineralization processes:
• Biologically induced: comes from the interaction of biological activity and the environment.
• Biologically controlled: the organism controls the creation of the biomineral.

Shells correspond to the second type of biomineralization, as do our teeth and bones. We make biominerals too!
This type of biominerals are characterized for having complex morphologies, controlled aggregation and texture, preferential crystallographic orientation, well defined structures and compositions and high levels of spacial organisation. I think we can tell all this from just looking at them, dreamy and full of math.

Biominerals are made from, well, both mineral and organic components. 50% of biominerals contain calcium with calcium carbonate as the most abundant compound. Carbon dioxide near seawater breaks down into carbon and sea organisms like molluscs and fish turn some of it into calcium carbonate (CaCO3).
How do shells grow? An answer by a non-artist & non-conchologist:
Shells contain 2% protein and the rest of the material precipitated (or layered) is a mix of different biominerals, I came across this very useful metaphor to understand the role of protein in building shells: the steel and concrete analogy. Protein works as steel forming the matrix and the mineral acts as the concrete that will be poured onto this matrix. Shells have 3 layers, the top layer is called periostracum and is made from a protein called conchiolin. The layer closest to the mantle is also known as nacre, the iridescent substance made from crystal aragonite platelets which disperse light and make it so beautiful. Mantle tissue inside the shell secretes the mineral and protein from the inside out – the oldest layer is on the outermost part of the shell and youngest layer is closest to the mantle tissue. Questions for upcoming weeks and other stuff
So, some questions have been answered. However, calcium carbonate is alkaline (pH 9.91) and since carbon dioxide is absorbed by seawater lowering carbonate ion concentration, a.k.a. ocean acidification, what’s the relationship between this and all the living systems in the ocean that produce and use calcium carbonate?
Week 5 I look forward to you.
In the mean time, let me finish this post by saying that I share the same sentiment as fellow blogger Penny Insole who said that she didn’t find this week’s content as challenging as week 2. Me too! Everything was pretty straightforward, except the bit about how Antarctica loses mass and how its ice melts.
I’d like to add that I found some of the resources useful because my dissertation (still cold as Snowball Earth) involves climate change and trying to link it to the recent coffee rust outbreak in the American continent, particularly in Colombia. Coffee rust is a fungus that needs free moisture to germinate and guess what I found on the extreme events tool? Well, well, well, if it isn’t an extreme rain and flood event in 2011 in Colombia related to La Niña. Heavy rainfall and floods related to La Niña in 2011 – this is an awesome clue. Anyway, statistics will tell if there is a true relationship between this extreme rainfall event and the devastating coffee rust outbreak. I’ll definitely talk more about my dissertation in September when it’s done.
If you enjoy climate tools like this, why not check out the great climate analogues tool.
See you next week and I’m always happy to read your blogs too so please link to them in the comment section below. Josh, another MOOC assistant, is blogging to create a glossary of key terms, check out his blog here. Thank you for reading.



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