Abstract:Geodynamic Mantle Modeling and its Relation to Origin and Preservation of Life
Geodynamic Mantle Modeling and its Relation to Origin and Preservation of Life
Uwe Walzer and Roland Hendel
Institut für Geowissenschaften, Friedrich-Schiller-Universität,
Humboldtstr. 11, 07743 Jena, Germany, u.walzer@uni-jena.de
Summary.
Section 1 refers to hypotheses on the origin of life. These different
hypotheses require distinct geodynamic and structural-geology prerequisites. E.g.,
in case of chemoautotrophic metabolism-first hypotheses, a plate-tectonic mechanism
is necessary that contains sites of reducing volcanic exhalations. It was shown
that the mass extinctions of biological species are influenced by the convectiondifferentiation
mechanism of the endogenic evolution of the Earth’s mantle. Especially
LIP-producing eruptions appear to be the principal reason for mass extinction
events. Occasionally, bolide impacts cause an extinction event in an ecologically
stressed, LIP-generated situation. Section 2 reports on our efforts pertaining to the
self-consistent modeling of plate tectonics. To facilitate plate-like motions, two conditions
are required, namely a low-viscosity asthenosphere and a deviation from the
purely viscous constitutive equation of the lithosphere. Our modeling results show
that already relatively simple additional assumptions in a 3-D spherical-shell model
of the Earth’s mantle produce oceanic lithospheric plates moving along the Earth’s
surface and changing their shape and size as a function of time. Section 3 describes
a new model of episodic growth of continental crust (CC). In the case of geneticsfirst
hypotheses or of metabolism-first hypotheses with solar irradiation or lightning
energy supply, the existence of CC with epicontinental seas, lagoons and ponds is
directly determining for the origin of life. Furthermore, the most important sources
of nutrients originate from the upper CC. We put a water-concentration dependent
solidus model of mantle peridotite into a 3-D spherical-shell, dynamic mantle model
with chemical differentiation that redistributes the heat-producing elements. As a
result, we obtain a set of temporal distributions of CC growth episodes that show
a certain temporal invariance for a variation of the melting-criterion parameter, f3.
The laterally averaged surface heat flow density qob, the Urey number Ur, and the
kinetic creep energy Ekin show temporally sinusoidal components superposing a
monotonously decreasing curve. Section 4 discusses partly unknown distributions of
physical quantities, the knowledge of which is necessary for the computation of a dynamic
Martian convection-differentiation system. It is ambiguous whether the early
strong Martian magnetic dipole was generated by the more effective core cooling
due to a plate-tectonic mode of solid-state convection in the Martian mantle during
the first 500 Ma. Section 5 outlines the numerical progress in the advancement of
2 U. Walzer and Hendel
the Terra code that was achieved by cooperation of the international group of Terra
developers.