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Comment by roenxi | Hacker News Reader

> Each of those iron 60–enriched layers marks a time during the past nine million years when Earth was bombarded by a nearby supernova.

As the article notes, this sounds like it is a remarkably common event. Dinosaurs only died out around 100 mya.

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Note that there are only 2 such layers. "60" refers to the Iron-60 isotope.

> Dinosaurs only died out around 100 mya.

Isn't 66 mya the generally accepted value?

At the time scales we're considering that's not even a rounding _error_.

40% is a rounding error? I hope not ;) (edit, fine 34%... but I'll say THAT might be a rounding error grin)

It's not 40%, though; the relevant 100% is not 100 million years, it's "several billion years".

I said specifically it's not a rounding error. You would, at minimum, round to the nearest hundred million years, which was done.

No. First, if the best known number is 66 mya, why throw away almost all the precision and call it 100 mya?

Second, the number it was being compared to in roenxi's comment was 9 million years, not 4 billion years.

So, yes, it is in fact a rounding error.

;-)

As numbers get bigger the amount of rounding gets more acceptable. 100 to 101 is as 1e100 to 1e101, despite te latter technically being off by 90%.

I think 100mya is perfectly fine. It doesn't undermine the point and this isn't trivia I plan to remember more accurately than that.

Yes, the Cretaceous–Paleogene extinction is agreed to be 66 mya with some surprisingly tight error bars of about 50k years.

But for the purpose of discussion 100 mya is close enough in terms of orders of magnitude so there's not a need to be pedantic.

I disagree. When one is only concernde about the order of magnitude, it should be given as 1*10^2 mya or as 0.1 bya. What the OP said is analogous to saying that one's grandfather died at the age of 100, when in reality he only lived to be 66.

I don't know if it will make you feel better or worse, but when writing the comment I looked up wikipedia, saw "66", thought "eh" and wrote 100.

If my grandfather had made it to 66 million I would have done the same thing.

According to this there would be 250,000 stars within a 250 light year radius from Earth: https://www.icc.dur.ac.uk/~tt/Lectures/Galaxies/LocalGroup/B...

So if all of those will explode eventually, that's a lot of supernovas (if the Earth is still around for all of those...)

Not all of those explode eventually, rather it's a small amount. Only the most massive stars explode into a supernova. The majority of stars are smaller, and will have different lifetimes. For example, the sun, an unusually bright star (brighter than about 95% of stars) will eventually turn into a red giant, slough off material then collapse to a white dwarf. It's estimated that the majority of stars are brown dwarf (very small, some not too-too much larger than Jupiter), and less than 1% of stars are massive enough to go supernova. The problem is that only the big stars go super nova, and the big stars also have the short lifetimes because they're burning fuel so quickly.

White dwarfs can also explode, if they are in a binary system. It's a different kind of explosion (more akin to a thermonuclear bomb) but it also produces iron.

> Dinosaurs only died out around 100 mya.

They did? I need only step into my back yard to see birds and lizards.

> remarkably common event

Probably not normally distributed but depends on the age of a given galaxy. But indeed, it does look like they are not super uncommon in our neighborhood.

I think parent meant the kind of dinosaur that can eat you.

The correct term is "non-avian dinosaur" for the ones that died en masse, but making that point in the first place is already pretty pedantic, doing it with snark is just being annoying for the sake of being annoying.

We're far off the topic of the thread which is iron-60 supernova paleoarchaeology but I can't help myself from pulling things even further off-course. Did you know there were flying dinosaurs in the medieval era that hunted humans from the skies?

- "'[Haast's] eagle had the possibility to hunt people,' Joanne says. 'It's hard to imagine a bird in that role but if it could successfully hunt a 250kg moa, then 80kg humans were possibly on the menu. There is oral tradition which suggests it was the case.'"

https://www.nhm.ac.uk/discover/news/2021/december/worlds-lar...

https://en.wikipedia.org/wiki/Haast%27s_eagle

> It's hard to imagine a bird in that role

What? People have been imagining birds in that role for as long as there have been people.

Has Joanne never heard of rocs?

>> It's hard to imagine a bird in that role

Do they have to fly? Have you ever meet Ostrich or Rheas?

(Protip: Keep your fingers, food and everything shinny hidden. They will not eat your fingers, but I can't guaranty that.)

A giant Ostrich would make me very afraid, but the giant versions are extint.

PS: Goose are smaller but very mean. I'd be even more afraid of a giant goose if they were real.

While birds are technically a kind of dinosaur, lizards are not.

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