Comment by chasil | Hacker News Reader

Comment by chasil | Hacker News Reader

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As far as I understand, keeping such creatures alive would require facilities with enriched oxygen. If the large ones escaped, they would suffocate.

"...large dinosaurs really required to be living in an oxygen tent. An atmosphere in the neighborhood of 35 percent oxygen would be considerably more compatible with large dinosaurs than one in the neighborhood of 28."

Volcanic activity in the Cretaceous enabled these high oxygen levels.

"The Cretaceous is clearly a green house period as opposed to the present ice house that we have... One of the problems that people have always suggested about these high levels of oxygen at various times in the past, is that this is comparable to what you have in an oxygen tent in a hospital. And what about wildfires? What they forget is that the reason for this high oxygen is that there is also a high carbon dioxide level. We are talking about carbon dioxide levels 6 to 10 times the present carbon dioxide level. And that is more than enough to essentially combat wildfires."

https://profjoecain.net/wp-content/uploads/2018/06/robert-e-...

Oxygen only one part and for all we know there were other trace gasses in the air they required that we don't even know about.

There are all kinds of animals today we cannot keep alive in captivity because they require some sort of unknown sequence of environmental triggers to activate or deactivate various processes in their body.

For instance cheetahs are nearly impossible to breed in captivity because their mating process requires running for many miles to exhaustion. Without this the pregnancy rate is in the abyss even with artificial methods. There are endless examples thats just one off the top of my head.

We just need to create a cheetah racing league. Problem solved.

Makes me wonder what the evolutionary benefit of keeping such triggers are and makes me wonder if part of the reason for the drop in human fertility in parts of the world is due to us removing some of those triggers for ourselves.

Wait, why would carbon dioxide levels have any effect on wildfires more than, say nitrogen?

For wildfires, I would expect the proportion of oxygen to matter much more than other gasses not involved in combustion.

Perhaps there's a difference in humidity levels, and therefore specific heat of the air?

Nitrogen is inert. Combustion doesn't need nitrogen. It just basically fills space.

As far as wildfires go, so is carbon dioxide. CO2 is not a typical reactant of combustion.

Sure it does, it's a "product", so in principle it participates in the reverse reaction. This probably doesn't actually make a difference for combustion, although CO2 does apparently work a bit better than N2 for firefighting in spite of the added weight, but that seems usually attributed being heavier-than-air (heavier than O2!) and somewhat polar. Not sure how applicable that is to wildfires when it's the atmosphere, though.

Why would a 2% CO2 atmosphere combat wildfires? It's a non-reacting gas, but so is nitrogen... And yet, wildfires still happen, despite our 79% nitrogen atmosphere.

Venus has a CO2 atmosphere, so the upper bar is very high.

While it is true that there are no wildfires on Venus, there is also no wood, or oxygen. Any oxygen released immediately reacts with the dirt to make, largely, more CO2.

If you wanted to terraform Venus, you would need to make diamonds out of the air so the carbon wouldn't just burn again. The oxygen you release would then react with the dirt and rocks to make more familiar minerals, and more CO2, of course. For a long time.

The whole surface would be a mile deep in diamonds before you finished. Hardly any water: the solar wind, not deflected by a magnetic field, carried most of that off. She probably had a field when she still rotated fast enough.

Earth gets to keep her water because the moon keeps us rotating enough to keep a magnetic field. Mars lost his because he is too small to keep a liquid core to generate the field with.

Yeah, I was pointing out that atmos can store a ton of CO2, past a certain point life be damned. Our lungs only work on the differential in the air lower to our body's.

Hmm… I have a question inspired by your choice of phrases:

Is there a graph somewhere of Earth's mean sea level atmospheric pressure over time? Was it significantly different e.g. a billion years ago?

On mobile so I'll let other ppl sezrch. My $0.02: atmos pressure is a resultant of gravity, which is a result of mass.

The mass has reduced over time, due to solar wind blowing away our atmosphere. But compared with the mass of the friggin' earth, my intuition says atmos pressure has reduced only slightly

I see where you're going with that, but gravitational force is GMm/r^2, so the mass of the air column halving would halve the pressure, and the shell theorem implies that is exactly half and not even a rounding error on M because none of the air above (the only bit contributing to the pressure) can contribute to the gravity field.

First part is also why Venus, with a lower mass, is able to have about x89 Earth's atmospheric pressure.

This doesn't directly answer your question but adds some interesting context. Some dinosaurs shouldn't be able to fly in the current atmosphere:

https://lru.praxis.dk/Lru/microsites/hvadermatematik/hem1dow...

Luckily they evolved feathers and manage just fine.

They had feathers when they were dinosaurs, and they’re smaller now.

I can’t usefully comment on most of the actual science in that paper, but I already had reasons to expect significant changes to the total mass of the atmosphere before reading it — the difference between today and the pre-oxygen apocalypse era (~2.4 Gy) implies at least a change of either 0.21 bar (if the oxygen came from the water) or 0.07 bar (if it all came from CO2).

I have no idea what to also anticipate from geology, impacts, or other things life might do besides the GOE.

When they were feathered dinosaurs, though, they couldn’t fly.

Both unclear[0], and also given the end of that sentence, unimportant.

[0] https://en.wikipedia.org/wiki/Archaeopteryx#Flight

Well, maybe, but humans can live at altitudes with about to half our normal oxygen levels, so maybe dinosaurs would have similar tolerances.

Humans tolerate those altitudes very poorly. They suffer from health problems and miscarriages.

High-altitude genetic adaptations have been the subject of a fair amount of study; there are three major groups bearing such adapations: Tibetans, Ethiopians, and Andeans.

The Andean adaptation suite is noticeably more primitive and lower-quality; this is generally thought to be the result of having evolved only very recently, after humans made it to the Americas.

The Tibetan suite is so effective that part of it has been proposed to be the result of interbreeding between arriving homo sapiens and a different hominid species native to the Tibetan plateau.

Thanks. I didn't know Ethiopians were also in the altitude mutant club!

My anecdote is I travelled in Bolivia for 3 weeks. Never under 3700 meters. One day we climbed Uturunku (6008 meters) as part of a jeep tour, You start at 5100 meters, so it's less crazy than it sounds.

Of the 6 tourists starting, only 3 made it up, with some real struggles.

Meanwhile, our native guide seemed to just have a relaxing walk...

Humans are really exceptional in their ability to survive in a large range of environments. If you do some reading about just how fragile many if not most animals are in regards to their environment you will surprised that they exist at all.

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