The Laschamp or Laschamps event was a
geomagnetic excursion (a short reversal of the Earth's magnetic field). It occurred between 42,200 and 41,500 years ago, during the end of the
Last Glacial Period. It was discovered from geomagnetic anomalies found in the Laschamps lava flows in
Clermont-Ferrand
Clermont-Ferrand (, ; ; oc, label= Auvergnat, Clarmont-Ferrand or Clharmou ; la, Augustonemetum) is a city and commune of France, in the Auvergne-Rhône-Alpes region, with a population of 146,734 (2018). Its metropolitan area (''aire d'attrac ...
,
France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
in the 1960s.
The Laschamp event was the first known geomagnetic excursion and remains the most thoroughly studied among the known geomagnetic excursions.
Background and effects
Since its discovery, the magnetic excursion has been demonstrated in geological archives from many parts of the world.
The transition from the normal field to the reversed field lasted approximately 250 years, while the magnetic field remained reversed for approximately 440 years. During the transition, Earth's magnetic field declined to a minimum of 5% of its current strength, and was at about 25% of its current strength when fully reversed. This reduction in geomagnetic field strength resulted in more
cosmic rays
Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our ...
reaching the
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's sur ...
, causing greater production of the
cosmogenic isotopes beryllium-10 and
carbon-14
Carbon-14, C-14, or radiocarbon, is a radioactive isotope of carbon with an atomic nucleus containing 6 protons and 8 neutrons. Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and co ...
, a
decrease in
atmospheric ozone
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
, and changes in atmospheric circulation.
This loss of the geomagnetic shield is claimed to have contributed to the extinction of
Australian megafauna, the extinction of the
Neanderthals
Neanderthals (, also ''Homo neanderthalensis'' and erroneously ''Homo sapiens neanderthalensis''), also written as Neandertals, are an extinct species or subspecies of archaic humans who lived in Eurasia until about 40,000 years ago. While ...
and the appearance of
cave art
In archaeology, Cave paintings are a type of parietal art (which category also includes petroglyphs, or engravings), found on the wall or ceilings of caves. The term usually implies prehistoric origin, and the oldest known are more than 40,000 ye ...
.
However, the lack of corroborating evidence of a causal link between the Laschamp event and
population bottleneck
A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as specicide, widespread violen ...
s of many megafauna species, and the relatively moderate radio-isotopic changes during the event, have cast significant doubt on the real impact of the Laschamp event on global environmental changes.
Because it occurred approximately 42,000 years ago, the period has been termed the Adams Event or Adams Transitional Geomagnetic Event, a tribute to
science fiction
Science fiction (sometimes shortened to Sci-Fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel uni ...
writer
Douglas Adams, who wrote in ''
The Hitchhiker's Guide to the Galaxy'' that "42" was the answer to life, the universe and everything.
Research
The Australian Research Council is funding research to analyze a
kauri tree found in New Zealand in 2019.
Radiocarbon dating
Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon.
The method was de ...
reveals that the tree was alive from 42,500–41,000 years ago, within the timeframe of the event.
See also
*
Solar cycle
The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surf ...
*
Solar cycle 1
Solar cycle 1 was the first solar cycle since extensive recording of solar sunspot activity began. The solar cycle lasted 11.3 years, beginning in February 1755 and ending in June 1766. The maximum smoothed sunspot number observed during the so ...
Notes
:1. The name derives from the Laschamps lava flows from which it was discovered, but appears as 'Laschamp' in most scientific literature.
References
{{Reflist
Geomagnetic reversal
Pleistocene events