Oceans; an unsustainable pollution
Every day 8 million tons of waste resulting from human activities reach the oceans! The slow degradation of most of these materials ends up in huge dumps that endanger marine ecosystems.
Time of degradation in the oceans:
Paper bag - 4 weeks Milk carton - 100 years
Newspaper - 8 months Aluminum cans - 200 years
Cigarette - 3 to 12 months Carica - 300 years
Cloth - 6 to 12 months Plastic bottle - 450 years
Chewing gum - 5 years Disposable diapers - up to 1000 years
Painted wood - 13 years Fishing line - 650 years
Condom - 30 years Rubber tire - indefinite
Plastic bag - 50 years Battery - thousands of years
Fishing buoy - 80 years Radioactive waste - up to 250,000 years
Glass - 1 million years
See, listen and reach
The study of an ocean implies the use of several methods and techniques that allow the knowledge of the shape of the ocean floor, the observation/audio of what is going on in depth and the collection of the elements that compose it.
The ROV (Remotely Operated Vehicle) is one of the equipments used in oceanic exploration, allowing a diversity of techniques of study...
In the oceanic plate´s spreading zones, where the geothermal gradient is high and the fracture network is dense, the water/rock interaction is intense. As the water circulates through the fractures it warms up, allowing metals in the rocks to dissolve: when this fluid comes into contact with cold, oxygen-rich sea water, metals percipitate, mainly in the form of sulphides.
The interaction between geological and biological processes on the ocean floor induces the slow precipitation (a few millimetres per thousand to million years) of iron and manganese oxides and hydroxides rich in cobalt, nickel and platinum, which generally occur in the form of crusts (between 400 and 4000m depth) or nodules (between 4000 and 6000m depth).
Ocean floor hydrothermal vents were discovered in the late 1970s in the Pacific Ocean and have since been discovered all over the globe, including the Atlantic Ocean. In the 1990s several hydrothermal vents were discovered on the seabed in Portugal along the Mid-Atlantic Ridge and south of the Azores: Menez Gwen (840 to 970m deep). Lucky Strike (1100 and 1750m deep), Rainbow (around 2300m deep) and Saldanha (2200m deep).
an unusual landscape
Although the large terrains of the Moon have been known in some detail since Galileo's time, the same is not true for the ocean floor, which remains hidden by the water column. In fact, it is only very recently that technological advances have allowed the representation of the submarine topography.
The work that has been carried out in the last few years in order to prepare the proposal for the extension of the Portuguese continental shelf has made it possible, to obtain a bathymetric model with a detail never achieved before. It is now possible to take a wonderful virtual voyage of a newly discovered "World".
From the ocean floor of yesteryear to today's resources
On a planet where the tectonic system has been active for billions of years, the oceans are inevitably transient situations that are at the origin of mountain ranges. The deformation of the material accumulated in the oceanic depths represents a fundamental process in the genesis of the orogenic landforms. Therefore, it is not surprising that in many cases, the resources currently exploited on the continents had their initial genesis in processes currently under the ancient ocean floor.
Iberian Pyritic Belt
an iron and copper chain linking the Sado to the Guadalquivir
The Iberian Pyrite belt occupies a vast region of the lower Alentejo and Andalusia where more than 2500 million tons of massive sulphide ores occur. These deposits were formed at the bottom of a sea as a result of the strong hydrothermal activity which characterised this region during the end of the Devonian period, some 350 million years ago. Studies suggest that the metals found here were obtained from the meta-sedimentary rocks below the ore bodies by solubilisation processe of those rocks (leaching). The intense tectonic activity associated with volcanic activity favoured the structural location of the outflow channels of the ascending metal-bearing fluids.
The characteristic deposits of the Iberian Pyritic belt are, in general, strongly pyritic (pyrite is an iron sulphide), with locally significant concentrations of sphalerite (zinc sulphide), chalcopyrite (copper and iron sulphide) and galena (lead sulphide).
The abundance and size of these deposits make the Iberian Pyritic Belt the most important metallogenic province in the world for this type of ores.
The deposit of Neves Corvo? Different among equals?
The deposit of Neves Corvo has exceptional characteristics in the Iberian Pyritic Belt. The deposit contains very high tin contents, mainly in the form of casserite (tin oxide), and the geochemistry of its sulphide ores contrasts with that of the other deposits with regard, for example, to copper contents or copper/zinc carbonate ratios, characteristic of the province. The isotopic data available indicate that the metal supply regime at Neves Corvo diverges significantly from the sources that typify the Iberian Pyritic Belt, including additionally metal contributions related to deep sources, probably of magmatic-hydrothermal nature.
Marble Strip Estremoz-Borba- Vila Viçosa- Alandroal
Ancient coral reefs ???
Between Sousel and Alandroal there are vast marble deposits which have been exploited since Roman times. Understanding its genesis reveals a complex history where oceans and towering mountains were, in a remote past, the dominant landscape of the region where now predominate the Alentejo plains.Marbles are metamorphic rocks, i.e., they resulted from a set of transformations in the solid state that led to the reorganisation at atomic scale of the elements that constitute the preexisting rock.The marbles of the Alentejo were pure limestones deposited, in a shallow ocean, during the lower Paleozoic (somewhere between 400 and 540 million years ago). This means that during metamorphism there was no change in the chemical composition (both marbles and limestones are formed essentially of calcium carbonates in the form of calcite), but only a process of growth of the calcite crystals; the initial crystals reorganised themselves, growing due to the migration of their boundaries. For this process to have occurred, it was necessary that the initial limestones were subjected to temperatures in the order of 200 to 250ºC.
From the depths to the surface
Knowing that on average the temperature increases by about 30 to 40C for every kilometre we penetrate inside the Earth, we conclude that the ancient limestones must have been 6 or 7 km deep in relation to the surface. As in the case of an iceberg, each mountain has a root that is larger than the emerging surface, we wouldn't necessarily have mountains that are 7 km high, but only about 3 km high. Although it may seem strange, the movement of sediments from the ocean floor to greater depths is a normal situation in the formation of mountain ranges where deformation leads to thickening of the sedimentary sequences.Once transformed into marble by the pressure and temperature conditions existing there, it was only necessary to wait for the weathering agents to take effect, millimeter by millimeter, year after year, any mountain, however high it may be, always ends up being a transitory phenomenon in the immensity of geological time: the marbles of the region were finally at the surface.
Geological map of Estremoz
the basis for understanding the region
When we mark the distribution of different geological features on a topographic map with different symbols, we get a geological map.
For the same region, depending on the aspects studied, it is possible to construct several geological maps (e.g. hydrogeological, geothermal, seismic risk, structural or mining maps).
Often, the geologist compiles the maximum amount of information available on the same map in order to make it more useful. This approach is extremely important as geological mapping and is an indispensable aid for correct regional planning.
from rock to soil
How is the SOIL composed?
The composition of the SOIL is one of the most complex in nature...
When we walk on the ground in the middle of a field we can see that the soil is very different from the rocky material from which it was formed. It presents an enormous diversity of constituents, belonging to the three phases of matter (solid, liquid and gaseous).
The solid phase includes mineral matter, organic matter and organisms. In general it forms aggregates of elementary particles and organic matter.
Water and air circulate in the pores and between the particles.
An important soil characteristic is texture, which represents the quantity of sand (between 2 and 0.02mm), silt (between 0.02 and 0.002mm) and clay (less than 0.002mm) in the soil composition.
Several soil properties (eg the ability to supply nutrients) depend on the texture. However, other properties (e.g. permeability to water and air) also depend on the aggregates and the pores between the particles, which is called the soil structure.
These and other soil characteristics, such as colour, show how rock material can undergo changes that leave it unrecognisable in the soil.
Living beings have to adapt to very difficult conditions in about 20% of the total area of continents and islands occupied by permafrost, rocky surfaces and unstable sands. In contrast, living conditions are easier in the remaining 80% of the area that is covered by the soil.