Australia: The Land Where Time Began
A Geodynamo of Hadean to Palaeoarchean Age recorded by Single
According to Tarduno et al.
it is important for understanding the evolution of Earthís core,
atmosphere and life on Earth, to know when the Geodynamo began to
operate. In this paper Tarduno et
al. report full vector palaeointensity measurements of
zircons from the Archaean
to Hadean which bears magnetic inclusions from the
Jack Hills conglomerate, Western Australia, to reconstruct the early
history of the Geodynamo. Magnetic fields that vary between 1.0 and 0.12
times the recent field strengths at the equator have been recorded from
zircons dating to between 4.2 Ga and 3.3 Ga. A core-mantle heat flow
that exceeds the adiabatic value and suggests plate tectonics and/or
advective magmatic heat transport is required by a
Hadean geomagnetic field.
Terrestrial nitrogen isotope evidence supports the existence of a
terrestrial magnetic field earlier than the Late Heavy Bombardment, and
implies that the evolution of an atmosphere on both Earth and Mars was
regulated by dynamo behaviour.
The oldest geomagnetic field values that were previously reported,
dating to 3.45 to 3.2 Ga from magnetite bearing single feldspar and
quartz phenocyrsts from igneous rocks of the Nondweni and Barberton
Greenstone Belts, Kaapvaal Craton, South Africa (1-3), indicate a field
that was relatively strong, though the earlier history of the Geodynamo
is unknown. It is predicted by some thermal evolution models that a
geodynamo didnít exist prior to about 3.5 Ga (4).
Tarduno, J. A., R. D. Cottrell, W. J. Davis, F. Nimmo and R. K. Bono
Hadean to Paleoarchean geodynamo recorded by single zircon crystals."
Science 349(6247): 521-524.
|Author: M.H.Monroe Email: firstname.lastname@example.org Sources & Further reading