How do oysters make pearls? - Rob Ulrich
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Shells and pearls are examples of biominerals. Biominerals are complex biomaterials that are made of both organic (sugars and proteins) and inorganic (minerals) materials. Living things form biominerals to survive and include things like bones, teeth, and phytoliths: they are all around us and inside of us.
Understanding biominerals and biomineralization (the name for the process of forming biominerals) are active areas of research. The current earliest known record of biomineralization is ~810 million years-old unicellular eukaryotes––150 million years older than the first complex life (more than one cell).
Windows to the past
Through death, biominerals record life, and due to their durability, remnants or impressions of biominerals typically get preserved in sediment, forming what we know as fossils. When crystals grow, they record information about the environment they formed in. For biominerals, this means information about the animals and plants that formed them and/or the environments that they grew in. This can help scientists decipher what past environments and life what like. To find out more read this article about how measurements of dinosaur body temperatures shed new light on 150-year debate. If you're into climate change or the environment, check out this article abouthow biominerals are stepping stones for climate change research
Biominerals can be similar to their abiotic crystal counterparts; however, they can differ in size, shape, level of crystallinity, impurities, and properties. The difference in the information that gets recorded in biominerals depends on the level of control an organism has over its biomineralization process. The control over this process lies on a spectrum (To leaner more, head over to An Overview of Biomineralization Processes and the Problem of the Vital Effect.) For example, the Halimeda green algae appears to simply induce aragonite formation: there is some determination of where the crystals form, but there is no control over the composition or orientation of the crystals (See Biominerals and Fossils Through Time to learn more.)
Organisms that possess less control over their biomineralization tend to grow crystals similar to their inorganically-formed counterparts, and in turn, their chemistry correlates more directly with the conditions of their environment. On the other side of the spectrum, there are biominerals that form under high levels of control. Think about our bones: there are processes actively moving the building blocks––calcium, phosphate, and carbonate––from our food and inhaled air to the different parts of our body.
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