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Comment by jolmg | Hacker News Reader

I guess kiloyear is the new B.C. with the 2000 marking a new epoch. It really seems too shortsighted.

This comment thread sparked a new Wikipedia tangent for me:

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

Apparently, the "before present" time scale is commonly used in archaeology and geology, and uses an epoch date of Jan 1, 1950. And there're two reasons for this: radiocarbon dating was first standardized in the 1950s, using a reference sample from 1950; and after the 1950s, widespread nuclear testing made radiocarbon dating inaccurate.

It's actually less arbitrary and shortsighted than it seems. Future civilizations are going to face a discontinuity in the archaeological record, and it'll be roughly at the Before Present epoch date.

Makes you think about the impact of nuclear testing... What else is impacted by these tests?

> Low-background steel is any steel produced prior to the detonation of the first nuclear bombs in the 1940s and 1950s. With the Trinity test and the nuclear bombings of Hiroshima and Nagasaki in 1945, and then subsequent nuclear weapons testing during the early years of the Cold War, background radiation levels increased across the world. Modern steel is contaminated with radionuclides because its production uses atmospheric air. Low-background steel is so-called because it does not suffer from such nuclear contamination. This steel is used in devices that require the highest sensitivity for detecting radionuclides.

https://en.wikipedia.org/wiki/Low-background_steel

Apparently one source of low-background steel are ships built before 1945, especially military ships as they are large and can be in use for decades. The US navy has scraped a few old ships for this use and there are theories that some WW2 wrecks are being salvaged from the ocean bed for this purpose, but there is no conclusive evidence.

And not just before 1945: lead is used for radiation shielding, but freshly-mined lead is slightly radioactive itself... shipments of lead that were mined 2000 years ago and sitting at the bottom of the Mediterranean since then, much less so: https://www.nature.com/news/2010/100415/full/news.2010.186.h...

Not a lot globally and at this timescale. Radionuclides is about it.

Nuclear bombs put energy and radioactive particulates into the atmosphere. The effects of the radioactive particulates are fairly well understood. The amount of energy from even the largest bombs is negligible at those scales.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4165831/

The zero year for the "Before Present(BP)" timescale is 1950. BP was used by carbon dating scientists first and 1950 was a nice round date a few years before the year when carbon dating[1] no longer worked due to atmospheric nuclear testing.

[1]https://en.wikipedia.org/wiki/Radiocarbon_dating

The number of different dates corresponding to "present" or "modern" is ... dizzying.

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