Lightnews — Scholar-powered news

Cara Giovanetti @idontevencara.bsky.social · 3d

You're right it's definitely too bad that a lot of the references are behind paywalls--but it's extra frustrating when it's stuff that was written for broad audiences. But SciAm gives a few free articles a month, right? At least I was able to access this one without a subscription

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Cara Giovanetti @idontevencara.bsky.social · 3d

References
pubs.geoscienceworld.org/gsa/gsabulle...
www.nature.com/articles/s41...
onlinelibrary.wiley.com/doi/full/10....

Further reading
www.scientificamerican.com/article/tree...
phys.org/news/2019-06...
www.discovermagazine.com/the-first-tr...

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Cara Giovanetti @idontevencara.bsky.social · 3d

The same thing happens with phosphorous fertilizers today; there’s a huge dead zone in the Gulf of Mexico where fertilizer runoff is deposited by the Mississippi river. But when trees did it, it likely helped fuel the Devonian extinction, where at least 70% of all Earth’s species perished.

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Summer satellite observations showing the Gulf of Mexico dead zone. Redder regions have higher concentrations of sediment and phytoplankton, contributing to an environment with less oxygen for marine life.

Image and caption information obtained from https://serc.carleton.edu/microbelife/topics/deadzone/general.html, which includes credits to NASA and the NASA Mississippi Dead Zone web site.

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Cara Giovanetti @idontevencara.bsky.social · 3d

But trees aren’t the only plants who need phosphorous! Algae got a free lunch out of the trees’ hard work—when soil ran off into waterways, the algae population exploded due to this huge nutrient boost. And when the algae died, the decomposition process sucked all of the oxygen out of the water

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An algal bloom in a river at Anderson Lake State Park in Washington, USA.

Image credit wikipedia user ECTran71 via wikimedia commons, CC BY-SA 4.0

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Cara Giovanetti @idontevencara.bsky.social · 3d

Trees dredged up tons of phosphorous out of the ground when their root systems evolved ~370 million years ago. All of that phosphorous, once packed tightly below the surface, scattered easily once these trees started dying and creating soil. Eventually that phosphorous ran off into waterways.

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Soil runoff to a waterway in Costa Rica.

Image credit wikipedia user Kentmanning via wikimedia commons, CC BY-SA 4.0

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Cara Giovanetti @idontevencara.bsky.social · 3d

But to get this to work, trees need to concentrate minerals. The tree gets a boost from minerals dissolved in the water it draws into itself, but it needs to spend a lot of energy on pumps in its cells that draw minerals in—a worthwhile expenditure since the tree needs minerals to survive.

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Cara Giovanetti @idontevencara.bsky.social · 3d

Water absorption in trees can occur pretty passively. Trees concentrate minerals in their roots, which means the ratio of minerals to water is almost always higher in the tree root than it is in the surrounding environment. This means water naturally diffuses into the root via osmosis.

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A diagram of osmosis--the natural, equilibrium state of this system is for the water column to be taller on one side of the barrier than the other, because nature wants to have the same concentration on both sides of the barrier.

Image credit wikipedia user Llywelyn2000 via wikimedia commons, CC BY-SA 4.0. Image has been cropped to remove text.

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Cara Giovanetti @idontevencara.bsky.social · 3d

It turns out humans aren’t the only living creatures to dredge up ancient material and spew it all back over the planet’s surface. When trees evolved deep root systems, they started to access all kinds of minerals in addition to the water they needed to survive.

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Cara Giovanetti @idontevencara.bsky.social · 3d

Trees: a symbol of a healthy ecology, clean air, and a tranquil environment.

And also maybe responsible for a mass extinction.

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A creepy-looking tree standing tall on a farm. It might have murderous intent!

Image credit Eric Johnson via wikimedia commons, CC BY-SA 3.0

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Cara Giovanetti @idontevencara.bsky.social · 11d

arXiv app when

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Cara Giovanetti @idontevencara.bsky.social · 11d

Recently it occurred to me that you can check the arXiv on your phone, and I went from never checking it to checking it on *Saturday*

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Reposted by Cara Giovanetti

Katie Langin @klangin.bsky.social · 12d

Today was a hard day for Ph.D. students who found out that they can no longer apply for NSF's prestigious Graduate Research Fellowship Program. "Devastating“ was how one student described it to me. #GradSchool #NSFGRFP

www.science.org/content/arti...

‘Completely shattered.’ Changes to NSF’s graduate student fellowship spur outcry

The announcement comes months later than usual, leaving many would-be applicants stranded

www.science.org

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Cara Giovanetti @idontevencara.bsky.social · 12d

Really torn up about whether I want to apply for Hubble again this year--of course the funding would be great, but I just can't bring myself to take half the broader impacts items off my CV

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Cara Giovanetti @idontevencara.bsky.social · 13d

LESS PROFICIENCY
MORE JOY

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Cara Giovanetti @idontevencara.bsky.social · 16d

Yes! I had to be really careful about how I discussed the reactivity of titanium oxide--it's not completely inert. In water it continues to react and forms a sort of porous structure that encourages bone growth into its gaps

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Cara Giovanetti @idontevencara.bsky.social · 16d

Yes, titanium implants are also generally considered safe when getting an MRI! Though apparently there's been some questions recently about whether skull/facial implants are safe in that setting

pmc.ncbi.nlm.nih.gov/articles/PMC...

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Cara Giovanetti @idontevencara.bsky.social · 17d

it's giving

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Cara Giovanetti @idontevencara.bsky.social · 17d

Good question! You're right that the orbital structure is similar, but there are more protons in the Zr nucleus and more electrons before you get out to the valence band. This leads to different properties of the solid metal--Zr is much more brittle than Ti, despite also being corrosion resistant.

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Cara Giovanetti @idontevencara.bsky.social · 17d

References

link.springer.com/content/pdf/...
journals.aps.org/prb/abstract...?
pmc.ncbi.nlm.nih.gov/articles/PMC...
www.aimspress.com/article/doi/...
link.springer.com/article/10.1...

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Cara Giovanetti @idontevencara.bsky.social · 17d

And its small number of electrons in its outer shell lead to only weak magnetic response. Paramagnetism, or magnetism induced by an existing magnetic field, works by aligning electron spins along the magnetic field—with few free electron spins, and those electrons spread out, the effect is weak

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A diagram showing the magnetic moments in a paramagnetic material. In the case of titanium, the moments are electron spins. The spins are disordered when a magnetic field is absent and ordered when a magnetic field is applied. Image credit wikipedia user ACGrain via wikimedia commons, CC BY-SA 3.0

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Cara Giovanetti @idontevencara.bsky.social · 17d

This means that, when titanium does bond, the result is usually pretty homogeneous. So you get a tough sheen of titanium oxide TiO2 that leads to corrosion resistance (rather than flaky rust on iron, which is the result of the formation of both FeO and Fe2O3 on the iron surface).

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A close-up of flaky rust on iron, which flakes off easily because multiple compounds of iron and oxygen form at the surface of the metal. Image credit Laitr Keiows for wikimedia commons, CC BY-SA 3.0

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Cara Giovanetti @idontevencara.bsky.social · 17d

Titanium has a nearly-empty outermost shell, which can hold a lot of electrons when full (2 electrons in 3d for those who remember their chemistry lessons). This means the number of ways titanium can bond with other elements are quite limited.

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Electron orbital diagram for titanium. The valence shell has only two electrons in it, and they're unpaired.

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Cara Giovanetti @idontevencara.bsky.social · 17d

But why does it have all of these magical properties?

They can all be traced back to the electronic orbital structure of titanium.

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Cara Giovanetti @idontevencara.bsky.social · 17d

Titanium’s durability is owed to small grain sizes—since the metal isn’t uniform over large scales, it’s harder for fault lines to spread. And it has low magnetic susceptibility, meaning in small quantities it doesn’t disrupt the magnetic fields conventional metal detectors use to detect metal.

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$Microstructure of a titanium alloy Ti–6Al–4V in a coarse-grained state. The grain sizes are very small, making it hard for fracture lines to spread through the material. Image credit Ratochka et al 2008, https://link.springer.com/article/10.1007/s11182-008-9093-3$

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Cara Giovanetti @idontevencara.bsky.social · 17d

Titanium is in fact so reactive that as soon as it's exposed to air, it reacts with oxygen and forms a thin, nearly-impenetrable, self-healing layer of titanium oxide, which is stable. After this reaction occurs, the titanium implant won’t continue to react in ways that could harm the recipient

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Optical microscope photo of stainless steel surface covered by titanium oxide colloid solution. Image credit Iuliia Karlagina for Wikimedia commons, CC BY-SA 4.0

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