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Hadley cells


I believe you are referring to Hadley cells.

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The diagram above shows all the circulation cells of the atmosphere, and you can see the ones just north and south of the Equator are called Hadley cells (named after George Hadley who first describe the mechanisms for trade winds).

At the equator the high amount of solar energy heats the atmosphere. There is a lot of moisture at the equator (there is a lot of ocean at the equator), and that adds water vapor to the atmosphere. Water vapor has a lower weight than nitrogen (the primary component of the atmosphere) and that lowers the weight of the atmosphere and therefore the pressure. Furthermore, as the air is heated it expands and that lowers the density causing upward motion of air. End result the air is rising.

As the pressure decreases with height the temperature decreases as well. This lowers the amount of water vapor the air can hold and cause precipitation. This is important later.

With lower pressure at the equator, the pressure gradient force (force causing air to move from areas of high pressure to areas of low pressure) brings air to the Intertropical Convergence Zone (named due to the incoming air converging). End result of this is surface winds move air toward the equator.

With air converging and rising at the equator, when it reaches the tropopause (top of the troposphere) it is forced to move outward away from the equator. As it moves further away, and as has further precipitation the weight of the air increases. This causes descending motion of air at around 30 degrees latitude. This air, as it descends also warms from the increase in pressure. This further dries out the air and increases pressure. This is why if you look around the globe you will see a lot of deserts at around 30 degrees latitude.

As you can see from the global diagram above this closes the system, giving you your Hadley cell.


One looks at types of rocks and their age, the other is just age


A geologic column (Stratigraphic column) is a representation of where different rocks sit relative to each other. A Strat column (for short) shows characteristic features of these rocks and can display their age. It is a good way to understand the geological sequence of an area.


A geological timescale is simply a scale that puts Earth's history into different eras, epochs and ages. Each section has an age attached to it, so you can look at it and say "500 million years ago, the Earth was in the Cambrian period". This time scale is being constantly updated as measuring the age of rocks becomes more precise. Here is the latest version:



craters, basaltic beds and dust.


Because of the absence of any atmosphere the Moon surface is not exposed to the weathering that is common on Earth. Therefore the landforms present are specific and long-lasting.

Craters: the impact of asteroids generates large craters (which are not of volcanic origin) clearly visible on the Moon surface. Several of those craters are surrounded by rings of deposits called "ejecta" which are composed by fragment of the surface projected around by the impact.

Maars (seas): are large flat areas covered by basalt relics of the primordial phase of the Moon genesis when volcanic activity was present and lava was emitted from fractures in the crust.

Dust: a thick layer of dust and small fragments of rock (regolith) covers most of the Moon surface. This was an initial concern during the planning of the Moon landing because there was a risk that these deposits could be so deep and loose to cause the sinking of the lunar module. This was not the case though.


The Mesozoic Era the age of dinosaurs is thought to have ended about 65.5 million years ago


A fossil strata containing dinosaurs are believed to be at least 65 million years old.

The most popular theory is that a comet or astroid struck the earth creating a dust cloud that changed the climate of the earth. The dinosaurs being ( at least mainly) cold blooded were not able to adapt to the rapid change in climate.

The early theory of Continental Drift, attributed the climate change to the rapid movement of the continents ( plates due to the modern theory of plate tectonics) causing increased volcanic activity creating dust clouds, that caused the climate change.

Another theory is that there was a disease that attacked the dinosaurs which swept across the world causing the dinosaurs to become extinct.


Gravitational pull of moon and sun on the Earth oceans and Earth rotation.


The gravitational pull of the moon and of the sun affects the oceans (and other large water bodies) of the Earth.

The water on the side of the planet closer to the Moon is attracted towards it generating a bulge; on the opposite side a similar bulge is created by the inertia of the water that tends to move away from the Earth due to the centrifugal force generated by the rotation of the planet.

In a theoretical homogeneous and continuous ocean two equal high tides and two equal low tides should follow each other within 24h.

This theoretical situation is modified by several factors:

  • The "lunar day" (that is the time required for any given point on the Earth surface to rotate from an exact position under the moon back to the same position) is of 24h and 50 minutes. This causes the cycle of high-tide / low-tide to be repeated every 12h and 25 minutes. It takes 6h and 12 minutes for the water along any given shore to go from high to low or from low to high.

  • The ocean is not continuous and its movements are affected by the surrounding land-masses thus causing changes in both timing and amplitude of the tides. Some areas experience two low and to high tides of similar amplitude each day following a "semidiurnal" cycle. When the tides differ in amplitude the cycle is called mixed. Finally other areas have one high and one low tide only each day and this cycle is called "diurnal"

  • The relative position of Moon and Sun affects the magnitude of the tides with the maximum high (or low) tide generated when the combined gravitational pull of the Moon and the Sun is the maximum (spring tides).

  • Specific topography of the shore can affect the magnitude of the tide. As example funnel-shaped bays may amplify the tide creating massive high and low tide. This is the case for the Bay of Fundy in Canada with tidal range up to 17 meters.

  • The combined effect of wind and tide can also enhance or reduce the magnitude of the tidal range.


See below...


The different types of fossils include:

  • Petrified fossils
  • Molds fossils
  • Casts fossils
  • Carbon films
  • Preserved remains
  • Trace fossils

Each of them form in different ways...

Petrified fossils:
Fossils often form when an organism’s remains become petrified, or “turned into stone.” In this process, mineral-rich water soaks into the small cavities and pores of the original organ- ism. The minerals precipitate from the water and fill the spaces.

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Molds fossils:
A fossil mold is created when a shell or other structure is buried in sediment and then dissolved by underground water. The mold reflects only the shape and surface markings of the organism. It doesn’t reveal any information about its internal structure.

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Casts fossils:
Cast fossils are created if the hollow spaces of a mold are later filled with mineral matter.

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Carbon films:
Fossils called carbon films can preserve delicate details of leaves and animal parts. The formation of a carbon film begins when an organism is buried under fine sediment. Over time, pressure squeezes out liquids and gases and leaves behind a thin film of carbon. Black shale often contains carbon film fossils. Sometimes, the carbon film itself is lost from a fossil. However, an impression of the fossil may remain.

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(From Google Image)

Preserved remains:

Sometimes, fossilization preserves all or part of an organism with relatively little change. The mammoth frozen in permafrost is one example. Another example is insects preserved in amber—the hardened resin, or sap, of ancient trees. The fly in Figure 10E was preserved after being trapped in a drop of sticky resin. Fossils can also form when remains are preserved in tar. Tar is thick petroleum that collects in pools at the surface. The La Brea Tar Pits in Los Angeles, California, have yielded preserved remains of ice-age mammals such as mastodons and sabre-toothed cats.

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Trace fossils:
Trace fossils are indirect evidence of prehistoric life. Tracks, like the ones in the picture below, are animal footprints made of soft sediment that later changed to sedimentary rock. Burrows are holes made by an animal in sediment, wood, or rock that were later filled with mineral matter and preserved. Some of the oldest known fossils are believed to be worm burrows. Coprolites are fossils of dung and stomach con- tents. These can often provide useful information regarding the food habits of organisms. Gastroliths are highly polished stomach stones that were used in the grinding of food by some extinct reptiles.

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