ATMOSPHERE An Introduction

Mr. Chad Lowe VillarroyaEarth Science

The Earth’s Atmosphere

Earth’s Atmosphere before Human’s lived

An atmosphere (from Greek ἀτμός - atmos "vapor" and σφαῖρα - sphaira "sphere") is a layer of gases that may surround a material body of sufficient mass,[1] by the gravity of the body, and are retained for a longer duration if gravity is high and the atmosphere's temperature is low. Some planets consist mainly of various gases, but only their outer layer is their atmosphere (see gas giants).

Introduction

The term stellar atmosphere describes the outer region of a star, and typically includes the portion starting from the opaque photosphere outwards. Relatively low-temperature stars may form compound molecules in their outer atmosphere. Earth's atmosphere, which contains oxygen used by most organisms for respiration and carbon dioxide used by plants, algae and cyanobacteria for photosynthesis, also protects living organisms from genetic damage by solar ultraviolet radiation. Its current composition is the product of billions of years of biochemical modification of the paleoatmosphere by living organisms

The atmosphere is a cloud of gas and suspended solids extending from the Earth's surface out many thousands of miles, becoming increasingly thinner with distance but always held by the Earth's gravitational pull.

The atmosphere is made up of layers surrounding the earth that holds the air we breathe, it protects us from outer space, and holds moisture (clouds), gases, and tiny particles. In short, the atmosphere is the protective bubble we live in.

This protective bubble consists of several gases (right) with the top four making up 99.998% of all gases. Of the dry composition of the atmosphere nitrogen, by far, is the most common. N2 dilutes oxygen and prevents rapid burning at the earth's surface. Living things need it to make proteins. Oxygen is used by all living things and is essential for respiration.

PIE GRAPH REPRESENTATION

Gas Symbol Content

Nitrogen N2 78.084%

99.998%

Oxygen O2 20.947%

Argon Ar 0.934%

Carbon Dioxide

CO2 0.033%

Neon Ne 18.20 parts per million

Helium He 5.20 parts per million

Krypton Kr 1.10 parts per million

Sulfur dioxide

SO2 1.00 parts per million

Methane CH4 2.00 parts per million

Hydrogen H2 0.50 parts per million

Nitrous Oxide

N2O 0.50 parts per million

Xenon Xe 0.09 parts per million

Ozone O3 0.07 parts per million

Nitrogen dioxide

NO2 0.02 parts per million

Iodine I2 0.01 parts per million

Carbon monoxide

CO trace

Ammonia NH3 trace

It is also necessary for combustion or burning. Argon is used in light bulbs. Plants use carbon dioxide to make oxygen. Carbon dioxide also acts as a blanket and prevents the escape of heat into outer space.

The atmosphere is rarely, if ever, dry. Water Vapor is nearly always present up to about 4% of the total volume. In the deserts regions (30°N/S) when dry winds are blowing, the water vapor content will be near zero. This climbs to near 3% on extremely hot/humid days. The upper limit, approaching 4%, is for tropical climates. The table below shows the change in atmospheric composition with inclusion of water vapor.

Gas Symbol Content

Nitrogen N2

78.084%

77.30% 76.52% 75.74% 74.96%

Oxygen O2

20.947%

20.74% 20.53% 20.32% 20.11%

Water Vapor

H2O 0% 1% 2% 3% 4%

Argon Ar 0.934% 0.92% 0.91% 0.90% 0.89%

The Earth's atmosphere is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night. Dry air contains roughly (by volume) 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and trace amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%.

Earth’s Atmosphere

The atmosphere has a mass of about five quintillion (5x1018) kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. An altitude of 120 km (75 mi) is where atmospheric effects become noticeable during atmospheric reentry of spacecraft. The Kármán line, at 100 km (62 mi), also is often regarded as the boundary between atmosphere and outer space.

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Mr. Chad Lowe VillarroyaEarth Science

The Origin of Earth’s Atmosphere

The Earth’s Atmosphere

Early Earth would have been very different and inhospitable compared to the Earth today. Hot◦   Why? - Primordial heat, collisions and compression during

accretion, decay of short-lived radioactive elements◦ Consequences - Constant volcanism, surface temperature too

high for liquid water or life as we know it, molten surface or thin, unstable basaltic crust.

Atmosphere - early atmosphere probably completely different in composition (H2, He)

Cooling◦  Primordial heat dissipated to space◦ Condensation of water (rain), accumulation of surface water.◦ Accumulation of new atmosphere due to volcanic out gassing◦ Conditions appropriate for evolution of life

Introduction

Composition - Probably H2, He These gases are relatively rare on Earth

compared to other places in the universe and were probably lost to space early in Earth's history because◦ Earth's gravity is not strong enough to hold lighter

gases◦ Earth still did not have a differentiated core (solid

inner/liquid outer core) which creates Earth's magnetic field (magnetosphere = Van Allen Belt) which deflects solar winds.

Once the core differentiated the heavier gases could be retained.

First Atmosphere

Produced by volcanic out gassing.   Gases produced were probably similar to those created by modern volcanoes (H2O, CO2, SO2, CO, S2, Cl2, N2, H2) and NH3 (ammonia) and CH4 (methane)

No free O2 at this time (not found in volcanic gases).

Ocean Formation - As the Earth cooled, H2O produced by out gassing could exist as liquid in the Early Archean, allowing oceans to form.◦ Evidence - pillow basalts, deep marine seds in

greenstone belts.

Second Atmosphere

Today, the atmosphere is ~21% free oxygen. How did oxygen reach these levels in the atmosphere? Revisit the oxygen cycle: Oxygen Production◦   Photochemical dissociation - breakup of water molecules by

ultraviolet Produced O2 levels approx. 1-2% current levels

At these levels O3 (Ozone) can form to shield Earth surface from UV

◦ Photosynthesis - CO2 + H2O + sunlight = organic compounds + O2 - produced by cyanobacteria, and eventually higher plants - supplied the rest of O2 to atmosphere. Thus plant populations

Oxygen Consumers◦   Chemical Weathering - through oxidation of surface materials

(early consumer)◦ Animal Respiration (much later)◦ Burning of Fossil Fuels (much, much later)

Addition of O2 to the Atmosphere

Throughout the Archean there was little to no free oxygen in the atmosphere (<1% of presence levels). What little was produced by cyanobacteria, was probably consumed by the weathering process. Once rocks at the surface were sufficiently oxidized, more oxygen could remain free in the atmosphere.  During the Proterozoic the amount of free O2 in the atmosphere rose from 1 - 10 %. Most of this was released by cyanobacteria, which increase in abundance in the fossil record 2.3 Ga. Present levels of O2 were probably not achieved until ~400 Ma.

Iron (Fe) i s extremely reactive with oxygen. If we look at the oxidation state of Fe in the rock record, we can infer a great deal about atmospheric evolution.

Archean - Find occurrence of minerals that only form in non-oxidizing environments in Archean sediments: Pyrite (Fools gold; FeS2), Uraninite (UO2). These minerals are easily dissolved out of rocks under present atmospheric conditions.

Evidence from the Rock Record

Banded Iron Formation (BIF) - Deep water deposits in which layers of iron-rich minerals alternate with iron-poor layers, primarily chert. Iron minerals include iron oxide, iron carbonate, iron silicate, iron sulfide. BIF's are a major source of iron ore, b/c they contain magnetite (Fe3O4) which has a higher iron-to-oxygen ratio than hematite. These are common in rocks 2.0 - 2.8 B.y. old, but do not form today.

Red beds (continental siliciclastic deposits) are never found in rocks older than 2.3 B. y., but are common during Phanerozoic time. Red beds are red because of the highly oxidized mineral hematite (Fe2O3), that probably forms secondarily by oxidation of other Fe minerals that have accumulated in the sediment.

Conclusion - amount of O2 in the atmosphere has increased with time.

Chemical building blocks of life could not have formed in the presence of atmospheric oxygen. Chemical reactions that yield amino acids are inhibited by presence of very small amounts of oxygen.

Oxygen prevents growth of the most primitive living bacteria such as photosynthetic bacteria, methane-producing bacteria and bacteria that derive energy from fermentation. Conclustion - Since today's most primitive life forms are anaerobic, the first forms of cellular life probably had similar metabolisms.

Today these anaerobic life forms are restricted to anoxic (low oxygen) habitats such as swamps, ponds, and lagoons.

Biological Evidence

Atmospheric oxygen built up in the early history of the Earth as the waste product of photosynthetic organisms and by burial of organic matter away from surficial decay. This history is documented by the geologic preservation of oxygen-sensitive minerals, deposition banded iron formations, and development of continental "red beds" or BIFs

Mr. Chad Lowe VillarroyaEarth Science

How is the Earth’s Atmosphere Structured?

The atmosphere: the layer of gases that surrounds Earth.

The atmosphere is made mostly of Nitrogen (78%) and Oxygen (21%).

Pressure and water vapor concentration decrease as you go higher in the atmosphere.

The atmosphere has no definite outer boundary.

What is the atmosphere?

Earth’s atmosphere is divided into 5 layers that each have a unique temperature pattern.

The layers are separated by boundaries called pauses.

II. How is the atmosphere divided?

Picture of Earth’s Different Layers

Different Layers of the Atmosphere

Layers of the Earth's Atmosphere

The atmosphere is divided into five layers. It is thickest near the surface and thins out with height until it eventually merges with space. 1) The troposphere is the first layer above the surface and contains half of the Earth's atmosphere. Weather occurs in this layer. 2) Many jet aircrafts fly in the stratosphere because it is very stable. Also, the ozone layer absorbs harmful rays from the Sun.3) Meteors or rock fragments burn up in the mesosphere.4) The thermosphere is a layer with auroras. It is also where the space shuttle orbits. 5) The atmosphere merges into space in the extremely thin exosphere. This is the upper limit of our atmosphere.

Troposphere: the bottom layer of Earth’s atmosphere.

Most of Earth’s weather occurs in the troposphere.

The troposphere is much denser than the rest of the atmosphere.

As altitude increases in the troposphere, temperature decreases at a constant rate.

The troposphere contains nearly all of the atmosphere’s water vapor.

What is the troposphere?

The troposphere is the lowest layer of Earth's atmosphere. The troposphere starts at Earth's surface and goes up to a height of 7 to 20 km (4 to 12 miles, or 23,000 to 65,000 feet) above sea level. Most of the mass (about 75-80%) of the atmosphere is in the troposphere. Almost all weather occurs within this layer. Air is warmest at the bottom of the troposphere near ground level. Higher up it gets colder. Air pressure and the density of the air are also less at high altitudes. The layer above the troposphere is called the stratosphere.

The stratosphere is the second layer of Earth’s atmosphere.

It is approximately 40km thick. The stratosphere contains the ozone layer.

Temperature increases as you go higher in the stratosphere because the ozone layer absorbs the Sun’s Ultraviolet (UV) Radiation.

What are the stratosphere?

The stratosphere is very dry; air there contains little water vapor. Because of this, few clouds are found in this layer; almost all clouds occur in the lower, more humid troposphere. Polar stratospheric clouds (PSCs) are the exception. PSCs appear in the lower stratosphere near the poles in winter.

Ozone, an unusual type of oxygen molecule that is relatively abundant in the stratosphere, heats this layer as it absorbs energy from incoming ultraviolet radiation from the Sun. Temperatures rise as one moves upward through the stratosphere. This is exactly the opposite of the behavior in the troposphere in which we live, where temperatures drop with increasing altitude. Because of this temperature stratification, there is little convection and mixing in the stratosphere, so the layers of air there are quite stable. Commercial jet aircraft fly in the lower stratosphere to avoid the turbulence which is common in the troposphere below.

The ozone layer is contained within the stratosphere. In this layer ozone concentrations are about 2 to 8 parts per million, which is much higher than in the lower atmosphere but still very small compared to the main components of the atmosphere. It is mainly located in the lower portion of the stratosphere from about 15–35 km (9.3–22 mi; 49,000–110,000 ft), though the thickness varies seasonally and geographically. About 90% of the ozone in our atmosphere is contained in the stratosphere.

The mesosphere is above the stratosphere layer. The layer above the mesosphere is called the thermosphere

The mesosphere starts at 50 km (31 miles) above Earth's surface and goes up to 85 km (53 miles) high.

As you get higher up in the mesosphere, the temperature gets colder. The top of the mesosphere is the coldest part of Earth's atmosphere.

The temperature there is around -90° C (-130° F)

What is the mesosphere?

Most meteors burn up in the mesosphere. A type of lightning called sprites sometimes appears in the mesosphere above thunderstorms. High-altitude clouds called noctilucent clouds can form in this layer. Scientists use sounding rockets to study the mesosphere. The top of the mesosphere is the coldest part of the atmosphere.

Scientists know less about the mesosphere than about other layers of the atmosphere. The mesosphere is hard to study. Weather balloons and jet planes cannot fly high enough to reach the mesosphere. The orbits of satellites are above the mesosphere. We don't have many ways to get scientific instruments to the mesosphere to take measurements there. We do get some measurements using sounding rockets. Sounding rockets make short flights that don't go into orbit. Overall, there's a lot we don't know about the mesosphere because it is hard to measure and study.

Thermosphere : is the layer above the mesosphere.

The thermosphere extends from about 90 km (56 miles) to between 500 and 1,000 km (311 to 621 miles) above our planet.

The thermosphere is typically about 200° C (360° F) hotter in the daytime than at night, and roughly 500° C (900° F) hotter when the Sun is very active than at other times. Temperatures in the upper thermosphere can range from about 500° C (932° F) to 2,000° C (3,632° F) or higher.

As altitude increases in the thermosphere, temperature increases to 1000oC because of intense X-Ray and UV Radiation.

What is the thermosphere?

Although the thermosphere is considered part of Earth's atmosphere, the air density is so low in this layer that most of the thermosphere is what we normally think of as outer space. In fact, the most common definition says that space begins at an altitude of 100 km (62 miles), slightly above the mesopause at the bottom of the thermosphere. The space shuttle and the International Space Station both orbit Earth within the thermosphere!

Finally, the aurora (the Southern and Northern Lights) primarily occur in the thermosphere. Charged particles (electrons, protons, and other ions) from space collide with atoms and molecules in the thermosphere at high latitudes, exciting them into higher energy states. Those atoms and molecules shed this excess energy by emitting photons of light, which we see as colorful auroral displays.

Very high up, the Earth's atmosphere becomes very thin. The region where atoms and molecules escape into space is referred to as the exosphere. The exosphere is on top of the thermosphere.

What is the exosphere?

This is a picture which shows the Earth, its atmosphere (the clouds are likely in the troposphere and stratosphere), the limb of the Earth (the dark blue curve/edge which is the mesosphere and thermosphere), and the dark blue to black region of space (where our exosphere extends out to...).

The Atmosphere Temperature

Range

The Atmosphere Pressure Range

The Ozone Layer Ionosphere Homosphere and Heterosphere Planetary Boundary Layer

Other Layers of the Atmosphere

The ionosphere, the part of the atmosphere that is ionized by solar radiation, stretches from 50 to 1,000 km (31 to 620 mi; 160,000 to 3,300,000 ft) and typically overlaps both the exosphere and the thermosphere. It forms the inner edge of the magnetosphere. It has practical importance because it influences, for example, radio propagation on the Earth. It is responsible for auroras.

Ionosphere

The homosphere and heterosphere are defined by whether the atmospheric gases are well mixed. In the homosphere the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence.[3] The homosphere includes the troposphere, stratosphere, and mesosphere. Above the turbopause at about 100 km (62 mi; 330,000 ft) (essentially corresponding to the mesopause), the composition varies with altitude.

Homosphere and Heterosphere

This is because the distance that particles can move without colliding with one another is large compared with the size of motions that cause mixing. This allows the gases to stratify by molecular weight, with the heavier ones such as oxygen and nitrogen present only near the bottom of the heterosphere. The upper part of the heterosphere is composed almost completely of hydrogen, the lightest element

The planetary boundary layer is the part of the troposphere that is nearest the Earth's surface and is directly affected by it, mainly through turbulent diffusion. During the day the planetary boundary layer usually is well-mixed, while at night it becomes stably stratified with weak or intermittent mixing. The depth of the planetary boundary layer ranges from as little as about 100 m on clear, calm nights to 3000 m or more during the afternoon in dry regions.

Planetary Boundary Layer

Different Cycles in the Atmosphere

The Carbon Cycle

The Water Cycle

The Nitrogen Cycle

GROUP ACTIVITY

Work in groups to answer the following questions! For each

question, you will have 2-3 minutes to write it

down and discuss it with the people around you.

1. Which layer of the atmosphere do we live in?

2. What is the purpose of the earth’s atmosphere?

3. What is the atmosphere? 4. What is the region between the layers of the atmosphere called?

1. In the Troposphere.2. Our planet's atmosphere is where

the weather happens. It provides the oxygen needed for life, and keeps a more or less constant temperature on the planet. It also protects Earth and humanity from dangerous radiations from the Sun.

Answers:

3. The atmosphere surrounds Earth and protects us by blocking out dangerous rays from the sun. The atmosphere is a mixture of gases that becomes thinner until it gradually reaches space. It is composed of Nitrogen (78%), Oxygen (21%), and other gases (1%).

4. The region between layers is named with the same term as the lower of two layers, but adding "pause" at the end. For example, the transition boundary between the troposphere and the stratosphere is called the tropopause.