Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their characteristic remanent magnetization (ChRM), that is, the polarity of Earth's magnetic field at the time a stratum was deposited. This is possible because volcanic flows acquire a thermoremanent magnetization and sediments acquire a depositional remanent magnetization, both of which reflect the direction of the Earth's field at the time of formation. This technique is typically used to date sequences that generally lack fossils or interbedded igneous rock. It is particularly useful in high-resolution correlation of deep marine stratigraphy where it allowed the validation of the Vine–Matthews–Morley hypothesis related to the theory of plate tectonics.
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Magnetostratigraphy in the context of Early expansions of hominins out of Africa
Several expansions of populations of archaic humans (genus Homo) out of Africa and throughout Eurasia took place in the course of the Lower Paleolithic, and into the beginning Middle Paleolithic, between about 2.1 million and 0.2 million years ago (Ma).These expansions are collectively known as Out of Africa I, in contrast to the expansion of anatomically modern humans (Homo sapiens) into Eurasia, which may have begun shortly after 0.2 million years ago (known in this context as "Out of Africa II").
The earliest presence of Homo (or indeed any hominin) outside of Africa dates to close to 2 million years ago.A 2018 study identified possible hominin presence at Shangchen, central China, as early as 2.12 Ma based onmagnetostratigraphic dating of the lowest layer containing what may possibly be stone artefacts.The oldest known human skeletal remains outside of Africa are from Dmanisi, Georgia (Dmanisi skull 4), and are dated to 1.8 Ma. These remains are classified as Homo erectus georgicus.
Magnetostratigraphy in the context of Shangchen
Shangchen (Chinese: 上陈) is a Lower Palaeolithic archaeological site in Lantian County, Shaanxi, China, some 25 km south of Weinan.It was discovered in 1964, and excavated during 2004 and 2017.
Stone tools found at the site were dated based on magnetostratigraphy in a 2018 study. Possible artefacts were found in 17 layers, tentatively dated by their discoverers to between 1.26 Ma (palaeosol S15) and 2.12 Ma (loess L28). The date of 2.12 Ma predates the earliest known fossils of archaic humans in Eurasia (Homo erectus georgicus) by 300,000 years. Whether these potential tools were made by an early species in the genus Homo or another hominin species is unknown.
Magnetostratigraphy in the context of Paleomagnetism
Paleomagnetism (occasionally palaeomagnetism) is the study of prehistoric Earth's magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called paleomagnetists.
Certain magnetic minerals in rocks can record the direction and intensity of Earth's magnetic field at the time they formed. This record provides information on the past behavior of the geomagnetic field and the past location of tectonic plates. The record of geomagnetic reversals preserved in volcanic and sedimentary rock sequences (magnetostratigraphy) provides a time-scale that is used as a geochronologic tool.