The end of the Holocene seems near.
Scientists divide the history of the earth into geological eras. Well-known eras are for example the Cretaceous and Permian. We currently live in the Holocene. At least: officially. Because there are more and more voices to embrace a new geological era: the Anthropocene. This era would clearly distinguish itself from the Holocene; it is characterized by the significant impact that human beings have on the earth. Although the evidence for that significant impact is abundant, the Anthropocene is still not official and we therefore still live in the Holocene. This is mainly due to the fact that an era is only officially recognized if a globally occurring, characteristic of the Anthropocene can be identified. And that has not convincingly succeeded to date.
But a new study appeared in the magazine Scientific Reports, can change that. This is because the researchers are presenting the first precise global signal for the Anthropocene from the southern hemisphere. This is a peak in radio carbon originating from aboveground nuclear bomb tests.
The researchers studied a Sitka fir on Campbell Island (New Zealand). The fir is also called the lonely tree in the world, because the closest tree is more than 200 kilometers away (on the Auckland Islands). The researchers found a peak in radio carbon in the wood of this lonely tree. The peak dates from 1965 and is caused by repeated nuclear bomb testing in the northern hemisphere in the 1950s and 1960s.
"We are incredibly excited that we have found this signal in the southern hemisphere, on a remote island," says researcher Chris Turney. “Because for the first time it gives us a clearly defined global signal for the new geological era that can also be preserved in the geological archive; thousands of years from now, this peak can still be a perceptible marker for the human-induced transformation of the earth. "
Previous research has already shown that the peak in atmospheric radio-carbon in the northern hemisphere was reached in 1964. This peak can be read in the wood of European trees (which recorded the signal through photosynthesis). The same peak was therefore recorded in the southern hemisphere at the end of 1965. With that discovery, there is now a worldwide, precise and perceptible signal in the geological archive. And with that, the signal now meets all the requirements for a marker for a new era.
It is remarkable that it is precisely this Sitkaspar that provides us with evidence for such a global marker that bears witness to the impact of people on the planet. The tree does not occur naturally on Campbell Island, but was planted there by people in 1901. Although the tree has reached a height of ten meters and apparently does well in this climate that is unusual for it, it has never produced pine cones, suggesting that it actually never grew up. "It seems appropriate that this extraordinary tree, planted by people far from its normal habitat, also becomes a marker for the changes we have made on our planet," said researcher Mark Maslin. "It is further proof - if we already needed it - that in this new era no part of our planet has been affected by humans."