Can nuclear weapons fallout mark the beginning of the Anthropocene Epoch?

摘要

Many scientists are making the case that humanity is living in a new geological epoch, the Anthropocene, butudthere is no agreement yet as to when this epoch began. The start might be defined by a historical event, such asudthe beginning of the fossil-fueled Industrial Revolution or the first nuclear explosion in 1945. Standard stratigraphicudpractice, however, requires a more significant, globally widespread, and abrupt signature, and theudfallout from nuclear weapons testing appears most suitable. The appearance of plutonium 239 (used in post-ud1945 above-ground nuclear weapons tests) makes a good marker: This isotope is rare in nature but a significantudcomponent of fallout. It has other features to recommend it as a stable marker in layers of sedimentary rock andudsoil, including: long half-life, low solubility, and high particle reactivity. It may be used in conjunction withudother radioactive isotopes, such as americium 241 and carbon 14, to categorize distinct fallout signatures inudsediments and ice caps. On a global scale, the first appearance of plutonium 239 in sedimentary sequencesudcorresponds to the early 1950s. While plutonium is easily detectable over the entire Earth using modern measurementudtechniques, a site to define the Anthropocene (known as a Ògolden spikeÓ) would ideally be locatedudbetween 30 and 60 degrees north of the equator, where fallout is maximal, within undisturbed marine or lakeudenvironments.