title: Geodynamo, solar wind, and magnetopause 3.4 to 3.45 billion years ago.
abstract: Stellar wind standoff by a planetary magnetic field prevents atmospheric erosion and water loss. Although the early Earth retained its water and atmosphere, and thus evolved as a habitable planet, little is known about Earth's magnetic field strength during that time. We report paleointensity results from single silicate crystals bearing magnetic inclusions that record a geodynamo 3.4 to 3.45 billion years ago. The measured field strength is approximately 50 to 70% that of the present-day field. When combined with a greater Paleoarchean solar wind pressure, the paleofield strength data suggest steady-state magnetopause standoff distances of < or = 5 Earth radii, similar to values observed during recent coronal mass ejection events. The data also suggest lower-latitude aurora and increases in polar cap area, as well as heating, expansion, and volatile loss from the exosphere that would have affected long-term atmospheric composition.
authors.affiliation: Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY 14627, USA. john@earth.rochester.edu
authors.forename: John A
authors.initials: JA
authors.lastname: Tarduno
authors.forename: Rory D
authors.initials: RD
authors.lastname: Cottrell
authors.forename: Michael K
authors.initials: MK
authors.lastname: Watkeys
authors.forename: Axel
authors.initials: A
authors.lastname: Hofmann
authors.forename: Pavel V
authors.initials: PV
authors.lastname: Doubrovine
authors.forename: Eric E
authors.initials: EE
authors.lastname: Mamajek
authors.forename: Dunji
authors.initials: D
authors.lastname: Liu
authors.forename: David G
authors.initials: DG
authors.lastname: Sibeck
authors.forename: Levi P
authors.initials: LP
authors.lastname: Neukirch
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Usui