Plutonium isotopes in the North Western Pacific sediments found | Hacker News Reader

Plutonium isotopes in the North Western Pacific sediments found

nature.com

71 pointsnixass19 comments

This is an impressive feat of analytical chemistry. Note the extremely low radioactivity of plutonium contained in their samples, which peaked at just over 7 millibecquerels per gram:

Total 239Pu + 240Pu activities in BMC19 core reach their maximum of 7.14 mBq/g at 48.5 cm bsf and then sharply drop to ca. 2.09 mBq/g.

For comparison, a single banana contains approximately 2000 times more radioactivity just from its naturally occurring potassium content:

https://en.wikipedia.org/wiki/Banana_equivalent_dose#Source_...

To be fair, how many single bananas were in their sample?

A banana's mass is on the order of 100g, so it's 20x as radioactive in terms of mBq/g, not 2000x

It's comforting to know that after we inevitably destroy ourselves in nuclear fire whatever crawls out of the leftovers will eventually find a strange plutonium signature at this moment in time and argue vigorously on their version of the internet about what it means.

Half-life seems to short, only ~88 years.

You appear to be referring to plutonium 238. This work analyzes the ratio between plutonium 239 and 240, which respectively have half lives of 24110 years and 6561 years.

https://en.wikipedia.org/wiki/Isotopes_of_plutonium#List_of_...

Unless it's a post WW-whatever-we-nuked recovery of humans or an offshoot again, the 6500 years halflife sounds likely to expire before a new scientifically intelligent species arises. Though I really hope things don't come to that.

Probably correct.

In most cases, isotopes can be detected for up to about ten half-lives, after which prevalence is reduce to 1/1,000th the initial concentration. In this case, that would be about 240,000 to 650,000 years.

For comparison, h sapiens seems to have diverged from its common ancestor to the other great apes about 2 million years ago, and achieved modern anatomical form about 200,000 years ago.

The period 240kya -- 650kya corresponds roughly to h. heidelbergensis.

https://en.wikipedia.org/wiki/Homo_heidelbergensis

The well-known organic-material radiodating isotope carbon-14 has a half-life of about 5,730 years, and is effective in dating materials to about 60,000 years ago.

We're going to need a bigger boat ^W^W longer half life.

Probably on the order of 200,000 to 10 million years.

But even if we cannot detect the original plutonium, we could detect the product of it’s decay - right?

For dating what's necessary is to measure the ratio of the elements.

Daughter / decay elements of plutonium don't indicate the initial quantity, and might (I'm not sure of this) also be the result of other decay chains.

Radiodating used to determine the age of the Earth relies on uranium-lead dating using samples found within zircon crystals. The crystals cannot form in the presence of lead, so any lead found within a crystal must have appeared there after the crystal formed. As both the mother uranium and daughter lead are within the same sample, the ratio can be clearly determined.

https://en.wikipedia.org/wiki/Uranium%E2%80%93lead_dating

Absent a similar containment for plutonium in the formations being described in TFA, that may not be possible.

For C-14 dating, the ratio of carbon isotropes within living tissue is known. The residual C-14 is what's left after the original organism has died, and the ratio then determines age. Given the short timespans afforded by C-14 dating, concerns with contamination or loss are lower.

Oh, well there goes any small comfort, into the void then!

You Maniacs! You blew it up! Ah, damn you! God damn you all to hell!

I hope that we do not destroy ourselves.

Whether we do or do not, it is sombering to know how much time our universe will spend without life, dark, bleak, and pointless.

https://m.youtube.com/watch?v=uD4izuDMUQA

Ah shucks ... I was hoping the Pu dated to sometime before the Holocene.

This is the earliest report of terrestrial plutonium predating the Holocene:

Nature volume 234, pages 132–134 (1971)

"Detection of Plutonium-244 in Nature"

Mass spectrometric measurements of plutonium isolated from Precambrian bastnasite confirm the presence of 244Pu in nature. Although the existence of 244Pu as an extinct radioactivity has been postulated to explain the xenon isotope ratios observed in meteorites, this is the first indication of its present existence in nature.

Plutonium 244 of course has a much longer half life (80 million years) than the isotopes analyzed in these sediments.

https://www.nature.com/articles/234132a0 (https://sci-hub.ru/10.1038/234132a0)

Good find, had never heard of that (discovered by Darlene Hoffman of Los Alamos in some CA phosphate). Guess the word didn't get around very fast, the 'man-made element' claim was around for a long time.

Here's some more, from Sci.American Mar 1998: [https://www.scientificamerican.com/article/do-transuranic-el...]

Would someone be willing to explain why this is important/significant? Asking genuinely.

It's about making the marker between geological epochs official.

Specifically the line between the Holocene (the past 12,000 years since the last glacial epoch) and the Anthropocene Epochs (the most recent period in Earth's history when human activity started to have a significant impact on the planet's climate and ecosystems).

The marker they are looking to make official is one that will survive for thousands of years and be independant of paper and electronic records, buildings, etc.

The paper fleshes out the properties and expected long term behaviour of the approximately 3 tons of Pu-239 released to the environment from above ground tests, which commenced in 1945 CE, and peaked in the Northern Hemisphere between 1961 and 1962 CE prior to being banned in 1963.

( assuming no additional above ground releases from the NATO-Russia exchanges of late 2022 | 2023 )

Thanks for the clear and concise explanation.

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