Characteristics of the Earth’s Atmosphere

The Earth’s atmosphere contains the air we breath. Atmospheric phenomena can provide a warm, sunny day for a picnic, an unexpected rainstorm to ruin an outdoor wedding, or a hurricane that can devastate entire regions. Climate change substantially involves changes in the atmosphere.

The Earth’s atmosphere, at its surface, is chiefly composed of 78% Nitrogen, 21% Oxygen (19), 1% Argon and trace amounts of other gasses such as water vapor, carbon dioxide and methane. (Source: NOAA).

Altitude versus temperature of the Earth’s atmosphere. Source: NOAA.

The atmosphere is composed of several layers (see figure). The density of the atmosphere decreases with altitude. The troposphere is the layer at the Earth’s surface and continues up to 10 km. Most cloud formation occurs in they layer. The temperature of the troposphere decreases with altitude up.

Above the troposphere is the stratosphere. Its temperature decreases with altitude. Above this, its temperature falls then rises due to other factors such as changing composition.

Surface Temperature and Energy Transport

The atmosphere is warm at the Earth’s surface and eventually reaches the cold temperature of space it its top. Heat is transported through the atmosphere by several mechanisms. Some heat is conducted through the atmosphere. Some heat is transported through bulk columns of rising warm air. Other heat is is removed by the action of storms and hurricanes. The amount of energy entering the Earth must be equal to the amount of Energy leaving the Earth over moderately long periods of time.

There are natural variations in surface temperature. The day side of the Earth typically has a lower temperature than the day side. The polar regions exhibit decreasing temperature with latitude and according to season. Surface features such as mountains, oceans and continents can lead to further temperature and weather variations.

Cloud Formation

Cloud formation is of tremendous interest because it has many effects. One effect is to reflect sunlight back into space. Another is to keep heat trapped at the Earth’s surface. Sunlight causes surface water and moisture to evaporate. Water vapor is less dense than air, so it tends to rise. Since the atmosphere near the surface becomes cooler with altitude, the water vapor will cool and condense, forming clouds. Clouds rise up to about 10 km. Under certain conditions, the tiny water droplets in clouds can coalesce into larger, heavier droplets, which can then result in rain.

Cloud columns rising on a warm day. Photo credit: NOAA.

Affect of Latitude

An important pattern is vertical air flows versus latitude. At the equator, the atmosphere is at its highest. There is literally an atmospheric bulge about the Equator. Warm, moist air rises high into the atmosphere. Circling the Earth about the Equator is the inter-tropical convergence zone (ITCZ) which is characterized by tall cloud columns and frequent storms (see figure).

Atmospheric cells form in intermediate latitudes. Hadley and Ferrel cells form from the Equator to about 30° latitude north and south. Air rises from the ITCZ, become cool and dry in the upper atmosphere, and then falls to the Earth at about 30°C. This is why many deserts, such as the Sahara, and Australian Outback form at these latitudes. At about 60° north and south, there is another zone of rising air and storm systems.

Vertical air flow by latitude and Hadley Cell. Photo credit: NOAA.

Energy Dissipation mechanisms and Structures

If there is sufficient energy in the atmosphere, strong thermodynamic potentials form, and complex structures emerge to more quickly dissipate that energy.

Such structures include connection columns and dust devils, as well as complex weather structures such as thunderheads, tornados and hurricanes.

Hurricane Joaquin

Geology As The Study of Processes

When most people view a rock, be it a mundane block of granite or a sparkling diamond, they regard it as a static object. When a geologist views a rock, they see the current result of a series of processes. Many geologic processes can take millions or even billions of years. Rocks and geologic formations each tell a story of what happened during those eons of time.

The Earth As A Living System

A physicist might define being alive as equivalent to producing entropy (e.g. consuming high level energy). A system is alive to the extent that is it producing entropy. By that definition, the Earth is an extremely lively planet. The Earth is a prodigious consumer of nuclear energy in its core. Heavy, radioactive elements are continuously decaying and producing a tremendous amount of heat. (This is why a cave can be much warmer than the Earth’s surface on a cold, winter day.) In this manner, the Earth is like a human, generating inner heat and shedding it into the atmosphere and ultimately into space.

Structure of the Earth

Interior of the Earth. Photo credit: USGS.

The Earth is covered with a rocky surface surrounding a hot inner, semi-liquid core. The interior of the Earth is heated by radioactive decay. Upon the interior, large granite continents on tectonic plates literally float and drift. Earthquakes can occur where these places grate, drag and overlap each other. The temperature of the Earth gradually decreases further from the center.

The Rock Cycle

Minerals at the surface initially formed due to volcanic activity. Such are called igneous minerals and include quartz, feldspar and basalt. They tend to be quite hard. However, on the surface, the surface breaks up into rocks, which are further worn down by heat, cold and water into sediments such as sands and clays. Such minerals are called sedimentary and can form into limestone and shale. If these minerals become trapped under other sediment under high pressure, the grains can attach to each other and form metamorphic minerals, such as quartzite and slate.

Rock cycle (credit: U.S. Geological Service)

Origin of Fossil Fuels

When organic matter gets trapped under layers of sediments, fossil fuels such as coal and petroleum can form. Carbon dioxide gets trapped in these fossil fuels until mined and burnt. Limestone also traps much carbon dioxide, until it gets used for concrete.

Implications of Geological Phenomena

Large volcanic eruptions can temporarily affect global weather by placing considerable dust and greenhouse gasses in the air. The tectonic plate movement may be involved in the sequestration of carbon dioxide ( Ward and Brownlee,  2000.) See video of Halema’uma’u explosive eruption below.

Reference

• Peter Ward and Donald Brownlee,  The Rare Earth, Why Complex Life Is Uncommon in The Universe, 2000.

Characteristics of the Oceans

Often overlooked in the geosciences, Oceanography concerns the oceans that cover two thirds of the surface of the Earth. The oceans have a tremendous impact upon weather and climate.

The oceans contain much more than pure water. Many dissolved minerals are present in the water, chiefly sodium and chloride (UIUC, Stanford), the constituents of ordinary table salt.. Gasses such as oxygen and carbon dioxide are also present. Most carbon dioxide absorption occurs in the oceans, either consumed by phytoplankton or absorbed into organic matter that often becomes limestone.

The depth of the oceans range from negligible at beaches to several kilometers in deep ocean trenches. Ocean temperatures are dependent upon depth, latitude and also currents.

Ocean Currents

An important topic in oceanography is the major oceanic currents that loop around the continents and affect navigation and climate (see figure).

Warm and cool ocean currents. Photo credit: NOAA.

Life and Pollution

The oceans contain tiny organisms near their surface called phytoplankton. These organisms utilize sunlight to convert carbon dioxide into oxygen and other molecules. Without phytoplankton, we would not have vital oxygen to breath. They are also the major source of carbon sequestration.

Phytoplankton (credit: U.S. National Oceanic and Atmospheric Administration)

The oceans contain much other life, such as crustaceans, fish, dolphins and whales, and above the surface, birds. Unfortunately, considerable quantities of pollution and waste also flow into the oceans. Of particular concern is plastic, which gets eaten by the sea creatures who cannot digest it and can die.

Reference

NOAA, http://oceanservice.noaa.gov/facts/phyto.html.

Sources of Energy

Sunlight is the chief source of energy for the Earth. Gravitational contraction provides a tiny amount. Tidal interactions with the Moon provide a small but significant amount at the surface. Radioactive decay provides an important source of energy below the Earth’s surface. The burning of fossil fuels can release considerable heat locally (enough to upset ecosystems), but the total amount of heat released is small compared to that from solar and radioactive heating.

Sun photographed in various wavelengths. (Credit: NASA)

Energy in the Atmosphere

The Earth is bathed in sunlight. Some of that sunlight is reflected back into space by the Earth’s surface and atmosphere. The reflectivity of the Earth is called its albedo. Some of the remaining sunlight directly heats up the atmosphere. A small amount is absorbed by processes such as photosynthesis.

Much of the remaining sunlight heats up the Earth’s surface. As surface temperature becomes raised, the Earth emits increasing amounts of infrared energy. This radiation in turn further heats the atmosphere.  Much atmospheric radiation is re-emited to the Earth’s surface. Some of it eventually makes it to the upper atmosphere and is radiated back into space.

The amount of energy entering and leaving the Earth’s atmosphere is called its energy balance. If more energy enters the Earth’s atmosphere than is emitted, the temperature of the Earth’s atmosphere increases. This is the current situation and is called global warming. Climate change results from global warming.

Energy flows to and from the Earth’s surface and atmosphere (credit: U.S. Govt.)

Resources

• NASA Earth Energy Budget poster

Further Reading

• NOAA Earth-Atmosphere Energy Balance
• NASA Climate and Earth’s Energy Budget (more detailed information)

Ecology involves the interactions between organisms, such as plants, animals and microbes, and their environment. There are several important concepts in ecology.

Ecology as a science

Environmental Envelope

A particular ecosystem exists within an environmental envelope. Parameters of that envelope include flows into and out of the ecosystem such as sunlight, water and material flows.

The envelope also include conditions within the envelope such as temperature and humidity. On a regional level, the result is the climate type, such as prairie, tropical rain forest or desert. For more information, read about the Köppen climate classification system.

Population

Population, also called stock, is the quantity of a particular organism. It is important because it indicates the magnitude of energy and nutrient flows through an ecological system. It is also a measure of momentum of energy consumption. Population typically refers to the count of a type of organism, such as individual tigers rather than each cell in a tiger’s body. Likewise, each ant in an anthill would comprise a counted individual, even though ants in such a hill are interdependent.

Food Webs

Food webs concern the integration between organisms in terms of what they eat and what eats them. Food chains also indicate the flow of energy and nutrients through a system. Generally, more complex food webs are more stable. In contrast, removing a single element from a simple food web can destabilize and even destroy that web.

Green field (Credit: US govt.)

At the base of all food webs is a means of capturing an external energy source, typically being sunlight, but sometimes more exotic sources such as hydrothermal vents. On land, including wetlands, green plants capture sunlight and form most of the base. Forests, grasslands, agricultural crops and even desert cacti form the base. In the oceans, phytoplankton capture sunlight and form most of the base.

Marine food web in Alaska (Source: US Govt.)

Population Dynamics

Food webs can evolve over time, in cycles and permanently. Predator-prey relations are an example of changes in the components of the food web over time. For example, if the population of predators grows too much, then over predation will occur. Consequently, the population of the prey falls, and can no longer support such a large population of predators. The population of predators falls, resulting on less pressure on the prey population, which then recovers. This cycle can repeat itself many times, as expressed in the Lotka-Volterra Predatory-Prey model (shown below in a systems dynamics process). Such Predator-Prey cycles  occur in human economies as well.

Click on the “Simul…” button to run the below simulation of the relation between a moose and wolf population where wolves prey on moose. Feel free to explore additional settings and options. You can even create your now account on the underlying Insightmaker platform and create your own simulations.

Further Reading

• Emergy Systems, University of Florida