https://en.wikipedia.org/wiki/Orbit_(anatomy)#/media/File:Ey...
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Looking at yourself in a mirror, if you hold your finger over the top of your nose your eyes will see under your finger. Move your finger just low enough so you’re seeing over it and you should be touching the bottom of your nasal bone. At that point your nose should be more than a finger width froward from the bottom of your orbital socket which is where the hole in skulls starts in those skulls.
Why is there a hole? Because your nasal canal extends inside your skull to connect with the back of your throat. I guess I don't fully understand the question there.
From memory it’s more like the stiff parts of your nose running near/along the bone and unlike your ears in any way.
Blood pH is regulated mainly by dissolved carbon dioxide and bicarbonate [1]. There's an order of magnitude less calcium in the blood, usually in the form of calcium phosphate, than either of those, and the amount is extremely tightly regulated within a very narrow concentration range -- far too narrow to have a notable effect on pH.
https://en.m.wikipedia.org/wiki/Calcium_buffering
I raised and homeschooled two kids and watched a lot of when dinosaurs ruled the earth type stuff. That's my source for the idea that a store of calcium was critical for allowing life to leave the ocean and I've tried repeatedly to search for additional info on this and can never find it.
I have no problem imagining that calcium is essential for buffering pH in land mammals and that free calcium ions simultaneously are tightly regulated and not directly used to move that number for the blood in short time frames. That actually fits perfectly well with my mental models that cellular acidosis is a more fundamental problem that fuels acidosis of bodily fluids.
If anyone has any good sources that might clarify this relationship for me, that would be cool.
HN != YC.
Except that’s not what’s going on.
The Wikipedia article lays it out. The amount of hydrogen ions someplace is what PH means, so controlling PH is controlling the number of hydrogen ions.
The same thing happens with calcium, but rather than doing the buffering it’s the number of calcium ions being controlled. Calcium buffering is controlling the number of calcium ions.
> Calcium buffering describes the processes which help stabilise the concentration of free calcium ions within cells, in a similar manner to how pH buffers maintain a stable concentration of hydrogen ions.[1] The majority of calcium ions within the cell are bound to intracellular proteins, leaving a minority freely dissociated.[2] When calcium is added to or removed from the cytoplasm by transport across the cell membrane or sarcoplasmic reticulum, calcium buffers minimise the effect on changes in cytoplasmic free calcium concentration by binding calcium to or releasing calcium from intracellular proteins. As a result, 99% of the calcium added to the cytosol of a cardiomyocyte during each cardiac cycle becomes bound to calcium buffers, creating a relatively small change in free calcium.[2]
In layman's terms, pH is a scale for measuring alkalinity vs acidity. Calcium is supposedly alkaline and high levels of intracellular calcium is associated with cell death (apoptosis).
So, for example, some people with CF avoid calcium because they think excess calcium causes cell death. But I think most likely excess calcium -- along with high levels of intracellular glutathione -- are a desperate attempt to buffer against something, including but not limited to excess acid.
So that's really what I'm interested in understanding. And also would love to see confirmation that calcium stores helped life leave the ocean and that wasn't something stupid and stated in error.
Though people with CF also likely misprocess sodium bicarbonate, in addition to being prone to very early onset osteoporosis (as early as their teens).
More precisely, calcium is an alkali earth metal (second column from the left in the periodic table), and those metals are so named because the compounds in which they were first discovered were alkalis. But that does not mean all calcium compounds are alkalis. For example, calcium citrate, which is a common way to convey calcium in supplements, can be weakly acidic in water solution (because of the citrate ion).
Most reliable sources of information describing calcium as alkaline stem from PRAL (potential renal acid load) and other kidney literature. Combined with the right chemicals (as you find in the kidneys), calcium does reduce acidity (contrasted with a buffering agent, the formulae are more linear, and a linear amount of other shit requires a linear amount of calcium or other alkalizing compounds to compensate) in the kidneys.
As something of a fun aside, most "alkaline diets" recommend a diet of weakly to strongly acidic foods which have an alkalizing effect on the kidneys and nearly no pH impact anywhere else in the body.
No comment on the rest. I just want to reiterate that acid/alkaline in one context (most commonly a description of the hydrogen concentration or other related ions) absolutely does not translate without extra effort and math and chemistry to other contexts (like anything describing calcium as alkaline). When those two ideas are mixed in presentation, a correct interpretation absolutely requires you to understand the details of what/where/why an author means when they refer to pH as something other than hydrogen/hydroxide concentration.
Breathing air came with challenges, though. A major one was getting rid of the air's carbon dioxide, which, when it builds up, reacts with water in the body and forms an acid.
Insects and friends manage to live on land just fine without any calcium bones.
What works once life is established on land can be different from what it took to transition to land and that's what I'm asking about.
https://forces.si.edu/atmosphere/02_02_06.html says
> As plants became firmly established on land, life once again had a major effect on Earth’s atmosphere during the Carboniferous Period. Oxygen made up 20 percent of the atmosphere—about today’s level—around 350 million years ago, and it rose to as much as 35 percent over the next 50 million years.
The high oxygen levels you mentioned occurred long after life had successfully made its way on land.
I'll take wikipedia as a reference (with reservations), but children's television shows?
Most land animals don't have a skeleton. Most land animals are insects and similar critters.
Well, the other reason sea life doesn't require rigid bones is that water provides a lot more buoyancy than air. Jellyfish work fine in the water; on land they're immobile puddles of glop.
The two ions that are present most often in seawater are chloride and sodium. These two make up over 90% of all dissolved ions in seawater.
The other ten percent are micronutrients that are also essential to life.
Most land animals have a skeleton not just to provide physical scaffolding to hang tissue on but because we need a store of calcium to mediate blood pH, something sea life doesn't require thanks to those minerals in the water. That's why you can have sharks which are mostly supported by cartilage with one set of bones: Their jaws.