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A practice where the use of a resource is balanced by the renewal of that resource.


If the use of the resource exceeds the renewal of that the resource the resource will be depleted. If the use of the resource greatly exceeds the renewal capabilities of the resource the resource may cease to exist.

The well managed use of forest is an example of a sustainable practice. The rate at which trees are cut down is regulated to equal the rate at which trees can be replanted and grown.

The fishing of salmon is another sustainable practice. The number of fish allowed to be harvested is regulated to allow enough Salmon to make up it upstream to regenerate the population of salmon.

The fishing of anchovies off the coast of Monterey in California is an example of a non sustainable practice. So many anchovies were caught that the breeding population dropped to near zero. Presently there are no anchovies to fish off the coast of Monterey.

The harvest of Otter skins is another example of a non sustainable practice. The otters were hunted to near extinction. Today the otter is still a protected species and no hunting of these scares animals is allowed.

Resources have to be carefully managed so that sustainable practices ensure that the use of the resource does not exceed the ability of the resource to be regenerated.


They are called "contour lines".


The contour lines are used to indicate the elevation on topografic maps. Usually, we use two types of lines to represent the landforms in a map. The regular line and the master line. The master lines, or master contours, are used to indicate, graphically, the elevation of the seccion of the relief, and they are represented in a different color on the map.

For example, in the map, below the contour lines are represented in red, and the master contours are represented in green.

enter image source here


OK ... not simple, but here goes.


I’ll explain a bit about the Sun, then a bit about the Earth, then put it all together.

The sun, whilst it appears to be a gently warming & beneficial, yellowish orb that reappears regularly (unless you live where I do) is actually an unconstrained nuclear fusion reaction of screaming intensity. The power it puts out as radiation is literally unimaginable.

Along with electromagnetic radiation of all frequencies, it also continually emits a stream (doesn’t convey the intensity I’m after, try torrent) of charged particles out into space. These charged particles are particularly intense when there are many sunspots. [It seems to have an 11 year cycle, but I’ll leave that bit.]

Next we need to understand our side. The earth’s outer core is a molten liquid, rich in iron. Due to the heat released by nuclear decay (predominantly in the inner core) there are strong convection currents circulating it. Recent evidence (https://phys.org/news/2016-12-satellites-jet-stream-earth-core.html) suggests this motion is much more energetic than previously thought. The motion of this conducting fluid gives rise to our magnetic field, which extends outwards into space. This is the magnetosphere, the region of space where earth’s magnetic field dominates that of the Sun.

When these charged particles emitted by the Sun, moving at millions of metres per second, collide with the earth’s magnetic field they are made to spiral in towards the poles. As they descend, still moving at tremendous velocities, they collide with atoms and molecules in the atmosphere.

This enetgises the molecules (lifts their electrons into higher orbits) and as they tumble back down, the electrons’ energy is released as light. If the molecule happens to be nitrogen (it often is, as nitrogen makes up about 78% of the air) then a red, violet or blue colour is seen. Oxygen molecules (the majority of the remaining atmospheric particles) tend to produce green or yellow colours.

Here’s the mechanism:

enter image source here

Taken from: http://earthsky.org/earth/what-causes-the-aurora-borealis-or-northern-lights

The whole show appears from the surface of the earth like curtains wafting in a breeze. I’m told it is exceptionally beautiful, but despite years of trying, have yet to see it.

Question #25038

Ms. Worth
Ms. Worth
Featured 4 months ago


a) Fold mountains are pushed up into anticlines and synclines.


Here is a diagram of fold mountainsenter image source here

The section on the right is a diagram of upward foldings called anticlines.

Downward folding creates synclines.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Here's another diagram showing the forces that crunch the earth's crust together so that it folds into mountains

enter image source here
~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Here's a photograph of fold mountains in Crete. It clearly shows the layers of the crust folded up into anticlines and down into synclines.

enter image source here

The European Alps are a famous example of a range of folded mountains.

  • Coniferous forests are well-adapted to the cold, the snow, and the winds, so forestry is economically important.
  • The terrain is too rugged and the weather is too cold for crop farming, but the wide valleys of the synclines are suitable for sheep farming and, at higher elevations, for goat farming.
  • Skiing and the associated tourism are a large source of income.
  • Hydroelectric power is common in the Alps. The numerous watersheds provide an abundance of water flowing into the deep U-shaped syncline valleys, which are dammed for the generation of hydroelectric power
    ~ ~ ~ ~ ~ ~ ~ ~

Other examples of fold mountains are the Himalayas, the Rockies, and the Andes.

Fold mountains are the highest mountains on earth.

You can find out more about folded mountains here:


Extinctions help geologist to establish relative ages for geological strata


Extinctions supply geologist with index fossils. A fossil of an organism believed to have gone extinct at a point in time provides clues about the age of the strata where the fossil is found.

For example all dinosaurs are believed to have become extinct about 65 million years ago ( perhaps by a catastrophic event). If a fossil of dinosaur is found, it dates the strata as being older than 65 million years.

Some index fossils that were believed to be extinct have been found alive even to the present. Still the theory of descent with modification and the proposed ages of extinctions are used by geologists as the primary means for dating strata containing fossils.


divergent plate boundaries are where convections current move upwards, and separate the plates.


At divergent boundaries new crustal material is brought to the surface. As the convection current comes to the surface it also moves outward in both directions (see image below). This causes the crust to separate into two different pieces.

An example of a divergent boundary is the mid Atlantic Ridge (there are mid ocean ridges in the Indian, and Pacific Oceans as well). The Mid Atlantic Ridge creates volcanos where the hot magma erupts from the underlining mantle. Many of these volcanos are undersea volcanos forming the mid Atlantic ridge. However in Iceland the the volcanos reach the surface forming the Island chain.

As the crust is pushed in two different directions it forms magnetic strips that are reflective and symmetrical on both sides of the Mid Atlantic ridge. This was part of the evidence that convinced Scientists that the theory of (Continental Drift) Plate tectonics was correct.

Divergent boundaries also create Rift Valleys and new oceans. The Rift Valley in East Africa is the result of a divergent boundary (image below). The Red Sea and the Dead Sea are thought to have been formed by the same divergent boundary.
Divergent boundaries, create mid ocean ridges, undersea volcanos, islands, rift valleys and new oceans.

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