1. Introduction

Geology is the study of the Earth’s crust and its continuous process of modification. At the beginning of solidification, approximately 3,9 Ga (giga annum = 109 years) ago, there were only Igneous Rocks, originating from the consolidation of the initial magma. With time these disintegrated due to the atmospheric chemical and physical actions, termed Weathering and Erosion respectively and the altered products were transported by gravity, air or water, and eventually deposited elsewhere, forming the Sedimentary Rocks.

The heat emanating from the Earth’s core is transferred to the mantle, therefore keeping it fluid and giving rise to convection currents which causes the Earth’s crust to be on a continuous reshaping mode. This is magnificently well explained by the Plate Tectonic principle, with plates breaking away from each other at the Diverging Boundaries, and pushing against each other, at the Converging Boundaries. Very briefly, we can have diverging boundaries where a continental mass is being split into two, or the split has a continent on one side and an ocean on the other, or there is ocean on both sides of the split, being the Mid Atlantic Oceanic Ridge the classic example of the latter. With converging boundaries we have for example the Himalayas being a consequence of the convergence between two continents, and the American western coast exemplifies a continental plate overriding an oceanic margin, the Pacific Ocean.

At the converging boundaries, with the impact between two plates, especially if both contain continental masses, we have the development of huge amounts of kinetic energy, a large proportion of which will be converted into heat. This, as well as the contact with the igneous rocks which continue being spewed from the mantle, causes a very marked change in the general characteristics, texture and composition of the rocks affected, thus Metamorphosing them. Finally, the mechanisms involved and the distortion caused to the rock masses when they are broken apart, or pushed together and its consequences, is studied under Structural Geology.

Following is an introductory presentation of these geological principles and mechanisms accompanied by examples photographed by me during my career. The sequence I will use is:

Igneous Rocks – after all these were the first solid substances on the Earth’s surface.

Weathering – which, it is fair to accept, was the initial action on the rocks by the atmosphere.

Erosion – occurring at the same time as weathering and adding to it.

Unconformity – which is a very important stratigraphic reference plane.

Sedimentation – since that is a consequence of the preceding actions.

Structure and metamorphism – topics I know even less about.

Prospecting – because, after all, in my days, that was what geologists were for.

Mining – again, that was why prospecting was done.

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One Response to 1. Introduction

  1. João Silva says:

    Great blog!

    Helpfull and interesting to read.

    obrigado from lisbon 😉

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