Analysis of the Earth and Environment Lecture 14: The Atmosphere

Question 1

Define the atmosphere

Answer 1

The envelope of gases surrounding the earth or another planet.

Question 2

What is the atmospheric pressure of Earth

Answer 2

Atm. Pressure at the surface of
the Earth is ~1013 hPa.

Question 3

Describe the composition of Earths atmosphere

Answer 3

78% Nitrogen
21% Oxygen
1% other gasses:
-0.93 %argon
-0.04% trace gases (including the greenhouse gases carbon dioxide, methane, nitrous oxide and ozone.)

Question 4

What are the four sections of the atmosphere

Answer 4

Split into 4 main layers based of Temperature

Troposphere
Stratosphere
Mesosphere
Thermosphere

Troposphere and stratosphere account for 99.9% of mass of atmosphere (almost half concentrated within 6 km of the Earth’s surface).

Question 5

Describe the Troposphere

Answer 5

The troposphere is the lowest section. Extends upward 6 - 10 km

We live in this part of atmosphere. Almost all weather takes place here - most clouds found here as 99% of atmospheric water is found here.

As you get higher in the troposphere the temperatures decreases

Question 6

Describe the Stratosphere

Answer 6

Extends from top of Troposphere about 50km

The Stratosphere contains the Ozone layer which absorbs high energy UV light converting it into heat. As a result, the higher you go in the Stratosphere the higher the temperature.

Question 7

Describe the Mesosphere

Answer 7

Extends from top of Stratosphere around 80km

Most meteors burn up in this layer

Mesosphere is the coldest layer of the atmosphere (-100 degrees centigrade)

Question 8

Describe the Thermosphere

Answer 8

Highest part of Earth’s atmosphere. Extends to between 500 to 1000km

Temperatures vary from 500 to 2000 degrees centigrade (or higher). However air is so thin up here that is not the same kind of temp experienced at surface.

Aurora occurs in thermosphere, as well as where international space station orbits

Question 9

Define the Barometric law

Answer 9

Pressure decreases exponentially with height above the Earth’s surface

Question 10

Describe the atmospheric composition and conditions of Mercury

Answer 10

Mercury’s gravity is around a third of that on earth so it cannot retain much of an atmosphere. Solar winds are also a big influence.

42% Oxygen
29% Sodium
22% Hydronium
7% Other gases

Question 11

Describe the atmospheric composition and conditions of Mars

Answer 11

Temperatures on Mars can reach 35 degrees C. The atmosphere is mainly CO2 so greenhouse effects are there,but with less gravity the volatiles escaped over time ? Now the pressure and concentration of the gas is very low (millibar).

95% Carbon Dioxide
3% Nitrogen
1.5% Argon
0.5% Other gasses

Question 12

Describe the atmospheric composition and conditions of Venus

Answer 12

Atmospheric pressure on Venus is around 92x that on Earth,mainly CO2,and a temperature of around 480 degrees C. Both are partly due to greenhouse effects.

96% Carbon dioxide
3% Nitrogen
1% Other gasses
Clouds of sulfuric acid

Question 13

Describe the origins of Earths atmospheric composition

Answer 13

1. Origins
   In the early years of our planet the atmosphere was composed of H and He: as the primordial disk from planetary formation.
2. Chemical/Pre-biological
   Atmosphere formed from volcanic outgassing dominated by water vapour,CO2,SO2 and other gases.
3. Microbial era
   Initial O2 formed through photodissociation, this allowed an ozone layer to be formed, early microbes emitted O2 as waste product.
4. Biological era
   Simultaneous decrease in atmospheric CO2 and the increase in O2 due to respiration/transpiration processes as life developed.

Question 14

Define the ionosphere

Answer 14

The ionosphere is the very upper part of the atmosphere that is ionized by solar
radiation. This is where the atomic oxidation number comes from.

Question 15

Describe how radiation interacts with the ionosphere

Answer 15

Solar radiation at ultraviolet (UV)and shorter x-ray wavelength are considered ionizing since photons of energy at these frequencies are capable of dislodging an electron from a neutral gas atom or molecule during collision.

At the same time, an opposing process called
recombination begins to take place
in which a free electron is “captured” by a positive ion if it moves close enough to it.

Question 16

Describe how radiation reacts with gasses

Answer 16

As the gas density increases at lower altitudes,the recombination process accelerates since the gas molecules and ions are closer together.

• The point of balance between these two processes determines the degree of ionization present at any given time.
• This is also what is constantly happening with ozone in the atmosphere,it is continually being formed and destroyed,it is the
  balance in that process that is important.
• CFC are now banned as refrigerant as these chemicals disturb this balance, removing Ozone at altitude. But at ground level,Ozone is a pollutant

Question 17

How is an ozone layer formed

Answer 17

The ozone layer is formed when ordinary molecules of oxygen gas (O2 ) in the stratosphere absorb UV radiation from the sun with wavelength <240 nm, which causes them to dissociate into single oxygen atoms.

Question 18

Define the Chapman mechanism

Answer 18

A theory for the origin of this ozone layer was proposed in 1930 by a British scientist, Sydney Chapman, and is known as the Chapman
mechanism.

Question 19

Describe the Decomposition of stratospheric Ozone

Answer 19

Ozone is a very reactive molecule and is termed a meta-stable molecule

• isolated molecules will decompose slowly
• when in contact with a molecule of another gas, it will react quickly.