Biogeochemical cycles - The lithosphere

Lithosphere = crust + upper portion of the mantle

Rocks and Minerals of the crust

Crust is the interface with the other geospheres

Heterogeneous mixture of different kind of rocks

Rocks are mixture of minerals (crystalline solid of specific chemical composition).

Formed from molten magma

Formed from compaction of sediments

Sedimentary that have undergone chemical transformations (high temp and pressure).

Plate tectonics

In the theory of plate tectonics, the outer part of the lithosphere is a composite of 20 separate rigid plates that move independently along the earth surface under the influence of convective currents driven by geothermal energy. The plates repose on the semi-rigid asthenosphere. Movements of a few to 10 cm per year.

Plate tectonics determines the topography of EarthFormation and spreading of sea floor in divergence zone.

Meanwhile sediments accumulates and are compacted on the sea floor forming rocks.

The sea floor (rocks) is eventually brought back to the surface in convergence zone through mountain building process.

‘Rock cycle’

Rock cycle

Element and nutriments buried as sediments in the oceans eventually return to continents (and to life !) .

Tectonics theory is the final link allowing to ‘close the biogeochemical cycle of elements’ .

…. How the Rock cycle can explain the paradox on the age of the ocean …

First which paradox ?

The global ocean occupies an estimated volume of 1.4E18 m3.This volume is maintained by a balance between input fro rivers and rain and evaporation.However the river erosion brings also some weathered detrital material and some dissolved nutriments to the ocean.It is estimated that the global erosion lowers the continents by 6cm every 1000 years, which equals to removal of 1.E10 m3 of continental material each year, and which eventually ends up in the ocean bottom. At this rate, the dumping of this material should the fill up the ocean within 140 Myears !So since the ocean exists, it should be younger than 140M years.

However the age of Earth is 4.9 Gy and there are geologic evidence that the ocean appeared 3.9 Gy ago. Also some shell fossils have been dated to 600 My … Do you see how plate tectonics and rock solves this paradox ?