Editing Earth's magnetic field (section)

=== Crustal magnetic anomalies ===
{{Main|Magnetic anomaly}}
[[File:Magnetic Field Earth.png|thumb|A model of short-wavelength features of Earth's magnetic field, attributed to lithospheric anomalies<ref>{{cite web |last=Frey |first=Herbert |title=Satellite Magnetic Models |url=http://core2.gsfc.nasa.gov/terr_mag/sat_models.html |work=Comprehensive Modeling of the Geomagnetic Field |publisher=[[NASA]] |access-date=13 October 2011}}</ref>]]

[[Magnetometer]]s detect minute deviations in the Earth's magnetic field caused by iron [[Artifact (archaeology)|artifacts]], kilns, some types of stone structures, and even ditches and [[midden]]s in [[archaeological geophysics]]. Using magnetic instruments adapted from airborne magnetic anomaly detectors developed during World War II to detect submarines,<ref>{{cite book|title=Geologic Applications of Modern Aeromagnetic Surveys|publisher=[[United States Geological Survey|USGS]]|year=1987|page=66|author=William F. Hanna|url=https://pubs.usgs.gov/bul/1924/report.pdf|access-date=3 May 2017}}</ref> the magnetic variations across the ocean floor have been mapped. Basalt — the iron-rich, volcanic rock making up the ocean floor<ref>{{cite journal|title=Basalts from the Deep Ocean Floor|author=G. D. Nicholls|journal=Mineralogical Magazine|volume=34|issue=268|year=1965|pages=373–388|url=http://www.minersoc.org/pages/Archive-MM/Volume_34/34-268-373.pdf|access-date=3 May 2017|bibcode=1965MinM...34..373N|doi=10.1180/minmag.1965.034.268.32|archive-url=https://web.archive.org/web/20170716230404/http://www.minersoc.org/pages/Archive-MM/Volume_34/34-268-373.pdf|archive-date=16 July 2017|url-status=dead}}</ref> — contains a strongly magnetic mineral (magnetite) and can locally distort compass readings. The distortion was recognized by Icelandic mariners as early as the late 18th century.<ref name="Kious">{{cite book |author=Jacqueline W. Kious |url=https://pubs.usgs.gov/gip/dynamic/developing.html |title=This Dynamic Earth: The Story of Plate Tectonics |author2=Robert I. Tilling |author-link2=Robert I. Tilling |publisher=USGS |year=1996 |isbn=978-0-16-048220-5 |page=17 |access-date=3 May 2017}}</ref> More important, because the presence of magnetite gives the basalt measurable magnetic properties, these magnetic variations have provided another means to study the deep ocean floor. When newly formed rock cools, such magnetic materials record the Earth's magnetic field.<ref name="Kious" />