scholarly journals A Rapid Change in Earth’s Mantle Geochemistry at 3.2 Billion Years ago Points to an Early Start of Plate Tectonics

2020 ◽  
Author(s):  
Hamed Gamal El Dien ◽  
Luc Doucet ◽  
J. Brendan Murphy ◽  
Zheng-Xiang Li
Keyword(s):  
Plate Tectonics ◽  
Rapid Change ◽  
Early Start ◽  
Earth’S Mantle ◽  
Mantle Geochemistry

scholarly journals Constraining crustal silica on ancient Earth

2020 ◽  
Vol 117 (35) ◽  
pp. 21101-21107 ◽  
Author(s):  
C. Brenhin Keller ◽  
T. Mark Harrison
Keyword(s):  
Continental Crust ◽  
Plate Tectonics ◽  
Incompatible Element ◽  
Silica Content ◽  
Efficient Mechanism ◽  
Element Abundances ◽  
Terrigenous Sediments ◽  
Earth History ◽  
Crustal Composition ◽  
Earth’S Mantle

Accurately quantifying the composition of continental crust on Hadean and Archean Earth is critical to our understanding of the physiography, tectonics, and climate of our planet at the dawn of life. One longstanding paradigm involves the growth of a relatively mafic planetary crust over the first 1 to 2 billion years of Earth history, implying a lack of modern plate tectonics and a paucity of subaerial crust, and consequently lacking an efficient mechanism to regulate climate. Others have proposed a more uniformitarian view in which Archean and Hadean continents were only slightly more mafic than at present. Apart from complications in assessing early crustal composition introduced by crustal preservation and sampling biases, effects such as the secular cooling of Earth’s mantle and the biologically driven oxidation of Earth’s atmosphere have not been fully investigated. We find that the former complicates efforts to infer crustal silica from compatible or incompatible element abundances, while the latter undermines estimates of crustal silica content inferred from terrigenous sediments. Accounting for these complications, we find that the data are most parsimoniously explained by a model with nearly constant crustal silica since at least the early Archean.

scholarly journals GEODYNAMICS

GEODYNAMICS ◽  
2011 ◽  
Vol 2(11)2011 (2(11)) ◽  
pp. 315-316
Author(s):  
V. V. Furman ◽  
◽  
M. M. Khomiak ◽  
Keyword(s):  
Finite Element ◽  
Numerical Modelling ◽  
Thin Plate ◽  
Thermal Convection ◽  
Plate Tectonics ◽  
Driving Forces ◽  
Finite Element Approach ◽  
Earth’S Mantle ◽  
Elastic Thin Plate ◽  
Element Approach

Thermal convection in Earth’s mantle are driving forces of plate tectonics. Combine model –viscous uncompressed mantle and thermo-elastic thin plate – is developed. The finite element approach in numerical modelling of geodynamical processes is presented.

scholarly journals Plate tectonics got an early start

Nature ◽  
2014 ◽  
Vol 506 (7489) ◽  
pp. 411-411
Keyword(s):  
Plate Tectonics ◽  
Early Start

Plate tectonics may have got a very early start

2020 ◽  
Vol 248 (3310) ◽  
pp. 12
Author(s):  
Michael Marshall
Keyword(s):  
Plate Tectonics ◽  
Early Start

High time resolution enzyme cytochemistry of rod outer segment

1990 ◽  
Vol 48 (3) ◽  
pp. 878-879
Author(s):  
Takuma Saito ◽  
Toshihiro Takizawa
Keyword(s):  
Enzyme Activities ◽  
Outer Segment ◽  
Rapid Change ◽  
High Time Resolution ◽  
Visual Cell ◽  
Enzyme Cytochemistry ◽  
Activation Effect ◽  
Rod Outer Segment ◽  
Enzymatic Cascades ◽  
Rapid Drop

Cells and tissues live on a number of dynamic metabolic pathways, which are made up of sequential enzymatic cascades.Recent biochemical and physiological studies of vision research showed the importance of cGMP metabolism in the rod outer segment of visual cell, indicat ing that the photon activated rhodopsin exerts activation effect on the GTP binding protein, transducin, and this act ivated transducin further activates phosphodiesterase (PDEase) to result in a rapid drop in cGMP concentration in the cytoplasm of rod outer segment. This rapid drop of cGMP concentration exerts to close the ion channel on the plasma membrane and to stop of inward current brings hyperpolarization and evokes an action potential.These sequential change of enzyme activities, known as cGMP cascade, proceeds quite rapidly within msec order. Such a rapid change of enzyme activities, such as PDEase in rod outer segment, was not a matter of conventional histochemical invest igations.

Sign in / Sign up

Export Citation Format

Share Document