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## Where are the oldest parts of the oceanic crust found?

David Drayer
Featured 4 months ago

The oldest parts of the oceanic crust are found farest from the mid ocean ridges at subduction zones and continental shelves.

#### Explanation:

New ocean crust is formed at the mid ocean ridges. The new crust is then pushed away from the ridge as newer crust comes to the surface. The ocean crust then spreads out enlarging the ocean.

The farer away from the ridge the ocean crust is the older the crust is. The oldest crust is at edges of the ocean. One place where the crust is the oldest is at edge of a subduction zone. It is here that the oldest ocean crust is pushed under a continental crust and destroyed.

In the image below, the oldest oceanic crust is pink/purple. As you can see, the newest crust (red) is adjacent to where there is seafloor spreading.

The continental shelves like the Eastern coast of the United States is another edge. The continents of Europe and North America are thought to have been connected at one time. A rift valley split the two continental crust apart forming an ocean between them. The continental shelf is where the new ocean started. This is where the oldest ocean crust exists.

Note no where on earth can the are the thick layers of old ocean sediments found in the geological column presently be observed.
The theory of plate tectonics does not seem to allow for the formation of thick deep ocean sediments.

## What do you call the lines on a topographic map that indicate the elevation of the land forms?

Eder Guedes
Featured 3 months ago

They are called "contour lines".

#### Explanation:

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.

## What are the Northern Lights?

Mark C.
Featured 3 months ago

OK ... not simple, but here goes.

#### Explanation:

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:

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.

## What is the relationship between the rock cycle and plate tectonics?

David Drayer
Featured 1 month ago

Plate Tectonics are key to the rock cycle, forming igneous rocks and recycling sedimentary and metamorphic rocks.

#### Explanation:

Basaltic igneous rocks are extruded at mid ocean ridges caused by divergent boundaries. Granite igneous rocks are extruded at volcanos caused by hot spots, and convergent plate boundaries like subduction zones. All igneous rocks the basis of the rock cycle are formed by plate tectonics.

The igneous rocks are eroded and turned into sedimentary rocks.
The sedimentary rocks layers generally tend to be recycled by plate tectonics. The deep ocean sediments are turned back into igneous rocks where they are pushed back into the mantle at subduction zones. This movement from igneous to sedimentary back to igneous is a major part of the rock cycle.

The heat from the mantle that fuels plate tectonics causes both igneous and sedimentary rocks to be turned into metamorphic rocks. The metamorphic rocks can be eroded into sedimentary rocks are remelted back into igneous. rocks. So the movement of metamorphic rocks in the rock cycle is also driven by plate tectonics.

## What are high altitude , high-velocity winds?

Ms. Worth
Featured 1 week ago

High altitude, high velocity winds are called $\text{jet streams.}$
https://quizlet.com/135896449/chapter-19-review-earth-science-flash-cards/

#### Explanation:

According to actforlibraries.org

• Jet streams are very fast moving currents of air found at about 10 km (6.2 miles) above the surface of the earth.
• The major jet streams usually follow an undulating narrow path from west to east.
• There are jet streams on both sides of the equator.
• Jet streams close to the poles are called polar jet streams
• Those at the tropics are known as subtropical jet streams, which are weaker than the polar jets.
• Jet streams form due to the orbital rotation of the planet, along with atmospheric variations in temperature, which produces strong winds.

Here is an image of the jet streams

Here's an AccuWeather illustration of how the jet stream brought the ultra-cold weather down from the Arctic to the eastern United States in the last few weeks

## Which part or Australia typically receives the most moisture?

Ms. Worth
Featured 2 weeks ago

The part of Australia with the most precipitation is the Tropical Climate area in the north

#### Explanation:

Rainfall in Australia tends to decrease as you move from north to south, and as you move from the east coast to the interior.

So the areas of high rainfall tend to generally occur in a curve from the north of the continent, then around to the east side, then down to the south.

Here is a color-coded map that shows the average yearly precipitation in Australia:

According to the web site "Climates to Travel,"
https://www.climatestotravel.com/climate/australia
the precipitation of Australia can be conveniently divided into four large regions:

1. Tropical climate (Darwin, Brisbane) --The rainiest area

3. Arid climate
4. South-east (Canberra, Sydney, Melbourne, Hobart)
$\textcolor{w h i t e}{m m m m m m m m}$_____

1. The Tropical Climate area

The vast northern area has a tropical climate, with a dry and sunny season ("the dry"), usually from May to October, and a rainy and muggy season ("the wet"), usually from November to April.

The annual rainfall exceeds 15.5" and is more abundant along the northernmost and the eastern coasts, where it exceeds 47".

The tropical rains occur mainly in the afternoon or evening in the form of downpours or thunderstorms. In the south-east, where Brisbane is located, the winter is cooler, so the climate becomes sub-tropical. Vegetation is savanna-type in the driest areas, with rainforests in the wettest part of the north-eastern coast.

In Darwin, the capital of the Northern Territory, 58.5" of rain per year fall, mostly between November to early April. The rainiest month is January, with almost 15.5" of rain. But from May to September it almost never rains.

Here is the average precipitation in inches for Darwin:

Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec|  YEAR
———————————————————————————
15 | 12 | 10 |  4  |  tr  | tr  | 0 |  0   |  tr  |  2  |   5  | 10 |    58.5

Here is a map of the Tropical Climate area

$\textcolor{w h i t e}{m m m m m m m m}$_____

2. The Mediterranean Climate
There are a couple of areas with a Mediterranean climate, with mild and rainy winters, and warm and sunny summers.

In Perth, Western Australia, 31.5" of rain falls in a typical year, most of which occurs from May to August, with a maximum of 6.7" in July, the central month of winter.

Here's a map of the Mediterranean climate areas of Australia:

$\textcolor{w h i t e}{m m m m m m m m}$_____

3. The Arid Climate
In the vast area called "Outback", the climate is arid, semi-desert (where annual precipitation is between 8 and 16" per year), or even desert (below 8" per year.)

In the semi-desert area, the rains in the north-central part fall in the form of downpour or thunderstorm in the hottest period, while in the southernmost part they occur mostly in winter.

In the most arid area, the rains are rare and sporadic, but every now and then a thunderstorm may erupt, most likely in summer.

Here is a map of the Arid Climate area

You can find out more about Australia's climate here:
http://www.abs.gov.au/ausstats/[email protected]/Lookup/by%20Subject/1301.0~2012~Main%20Features~Australia%27s%20climate~143

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