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Carbon dating challenge, friendship economics — the week in infographics

Carbon dating hampered

The burning of fossil fuels has shifted the composition of carbon isotopes in the air of the Northern Hemisphere enough to cancel out a signal, used in radiocarbon dating1, that stems from nuclear-weapons testing. Radiocarbon dating relies on the fact that living things absorb both stable carbon-12, which is the most common isotope, and a small amount of radioactive carbon-14 from the air. By measuring how much 14C is left in organic materials such as wood, fabric or bone, researchers can date them. In particular, the rapid spike in 14C released by nuclear-weapons testing between 1952 and 1962 has created a diagnostic ‘bomb curve’ that can provide a precise time stamp for organic materials formed between around 1960 and 2020. But the burning of fossil fuels has been rapidly releasing carbon dioxide that does not contain 14C. As of 2021, these two effects have cancelled each other out in the Northern Hemisphere, which could cause problems for valuable carbon-dating techniques.

Altered carbon: Line chart showing the proportion of radioactive carbon-14 in atmospheric carbon dioxide since 1950.

Source: Ref 1.

Friendships that enrich

The degree to which people of low socio-economic status make friends with individuals of higher socio-economic status during childhood is linked to economic mobility later in life, research published in Nature suggests2. Researchers measured this ‘economic connectedness’ in counties across the United States and collected data on the income mobility of people in those counties. They found that higher economic connectedness was associated with greater predicted future income rank. The work could inform policies aimed at improving social mobility.

A graph that shows predicted income rank against economic connectness on Facebook.

Source: Ref. 2

Ketamine’s short-lived buzz

Ketamine is a recreational drug that is also used as an anaesthetic and antidepressant. But how addictive is it? New research in mice suggests that ketamine is less addictive than cocaine — and that this could be because the drug produces a shorter burst of the reward chemical dopamine than does cocaine. Dopamine neurons are inhibited when a neurotransmitter, glutamate, binds to NMDA receptors in a region of the brain called the VTA (a). Writing in Nature, the researchers showed3 that in mice, ketamine blocks this inhibition by binding to NMDA receptors instead, leading to increased activation of dopamine neurons and triggering the release of dopamine (b) — a mechanism of dopamine release that differs from that triggered by addictive drugs such as cocaine. The researchers also found that this mode of dopamine release is rapidly quashed because the dopamine goes on to bind to a receptor that inhibits the dopamine neurons. By contrast, cocaine triggers sustained dopamine release.

Figure 1

Source: Ref. 3.



  1. Graven, H., Keeling, R. & Xu, X. Nature 607, 449 (2022).

    PubMed  Article  Google Scholar 

  2. Chetty, R. et al. Nature (2022).

    Article  Google Scholar 

  3. Simmler, L. D. et al. Nature (2022).

    PubMed  Article  Google Scholar 

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