Gases and Liquids in Mantle Rocks

الأحد مايو 17, 2015 4:42 pm

Gases and Liquids in Mantle Rocks

In the Investigate, you saw that before you opened a carbonated

beverage, you could not observe any bubbles. However, when you

opened the bottle, you observed bubbles form. The bubbles rose to the

surface of the liquid and escaped. The beverage was carbonated. It had

gas dissolved in it. Opening the bottle reduced the pressure on the fluid

in the bottle. This allowed the gas to be released. The reason you do not

see bubbles in an unopened bottle is because the pressure of the outside

of the bottle restricts the movement of the gas in the liquid. This

prevents the gas from escaping. Heating the opened bottle increases

the rate at which the gas escapes.

Gases are dissolved in Earth’s hot mantle

rocks. These include carbon dioxide,

nitrogen, and water vapor. Compare this

to the gas dissolved in the beverage that

you examined. Deep in the mantle rocks,

dissolved gases are under great pressure.

They remain dissolved and in equilibrium

with their environment. However, during

volcanic activity, molten rock rises

through the crust. The environmental

conditions change. As the depth below

the surface decreases, the mass of the

overlying crust decreases. Therefore,

the pressure on the rising magma also

lessens. With a decrease in pressure, gases

dissolved within the magma are released.

This creates a new equilibrium, similar to

the release of gas from the bottle after it

was opened.

Earth’s rocky lithospheric plates contain

special minerals. These minerals can hold

water within their crystals. Mineral matter

in Earth’s mantle also contains water. How much water vapor is in Earth’s

mantle? A number of years ago, scientists in Tokyo, Japan, tried to

answer this question. They created a model of Earth’s mantle in their

laboratory. The scientists placed the same pressures on their “minimantle” that exists in Earth’s mantle. This is about 250,000 times greater

than the atmospheric pressure you feel at Earth’s surface. They found

that at this great pressure the rocks in the mantle are able to contain

huge volumes of dissolved water vapor. The volume of Earth’s entire

mantle is enormous. The scientists determined that it could contain a

volume of water greater than all the water

in Earth’s oceans. Some scientists debate

these findings. They suggest that there may

not be that much water in the mantle. Since

it is impossible to gather samples of the

deep mantle, research and debate is still

continuing.

Many crystals in Earth’s crust begin to form

in some kind of fluid. As these crystals grow,

they often trap tiny bubbles of the fluid. This

provides important information about the

conditions under which the crystals formed.

By heating the bubbles, scientists can find

the temperature and pressure at which the

crystals formed. One instrument used for this

was designed by the USGS. It is extremely

sensitive. It is capable of detecting amounts

as low as 8 parts per billion in samples as

small as 0.01 mm in diameter.

Gases dissolved in Earth’s mantle are released into the atmosphere during

volcanic eruptions. These can occur when a plate descends downward

into the mantle. The plate can get so hot that any water or gas it contains

rises into the overlying mantle. The overlying mantle melts into magma.

The magma is less dense than the solid rock that surrounds it. It then rises

through the mantle to the overlying crust. As it nears Earth’s surface,

there is less overlying rock. The pressure on the magma decreases. At the

surface, the magma is under atmospheric pressure. Gases such as carbon

dioxide, nitrogen, sulfur dioxide, and water vapor dissolved in the magma

are released into the atmosphere. Various volcanic processes release

dissolved gases from Earth’s mantle. These include continental and

oceanic volcanic eruptions, outpouring of lava flows, and rifting. Also

included are rising plumes at hot spots and at mid-ocean ridges. During

these processes, hot material from the deep mantle reaches Earth’s

surface. As this takes place, any dissolved gases it contains are released.

الأربعاء مايو 20, 2015 9:50 pm

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الأربعاء مايو 20, 2015 11:25 pm

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Gases and Liquids in Mantle Rocks

Gases and Liquids in Mantle Rocks

رد: Gases and Liquids in Mantle Rocks

رد: Gases and Liquids in Mantle Rocks