Evolution of the Atmosphere

Evolution of the Atmosphere

Anticipation Guide Oxygen is the main gas found in the atmosphere The current atmosphere is the same atmosphere that the Earth had when it formed Water vapor is a gas found in the atmosphere The layers of the atmosphere are defined by temperature differences Weather is defined as the state of the atmosphere in the present

Focus Question Was our atmosphere always the same as it is today?

Enduring Understanding The composition of the Earth s atmosphere has changed over geologic time.

VA SOL SOL 12 The student will investigate and understand the origin and evolution of the atmosphere and the interrelationship of geologic processes, biologic processes, and human activities on its composition and dynamics. Key concepts include a. scientific evidence for atmospheric changes over geologic time; b. current theories related to the effects of early life on the chemical makeup of the atmosphere;

History of the Atmosphere The air we breathe today has not always been this friendly to life. Like Earth itself our atmosphere has evolved over geologic time and made necessary changes to be able to support life.

The Early (Precambrian) Atmosphere Hydrogen and Helium dominated Earths earliest atmosphere Gravity could not keep these lightweight gasses from escaping into space Heavier gasses such as CO2 and Nitrogen remained

Outgassing Much or Earths early atmosphere came from volcanoes in the form of outgassing as early volcanic activity shaped the planet s surface H2O, CO2, N, and CO are the most abundant gasses vented The early atmosphere also contained Methane (CH4) and Ammonia (NH3) as a result of chemical reactions among the volcanic gasses.

Oxygen Volcanoes do not outgas O2 which is vital for animal life to evolve outside of the oceans. This most commonly accepted to be from early forms of microscopic cyanobacteria (blue-green algae) that converted the abundant CO2 into O2 as they carried out their process of photosynthesis for energy

Photsynthesis In photosynthesis plants use solar energy to convert water and carbon dioxide into sugar for energy and tissue construction. Oxygen is given off as the waste product. Images\Atmosphere History.pdf

Ozone Oxygen is not only important for respiration. In the upper atmosphere it is split by high energy UV radiation and recombines to form a layer of O3 that protects us from the UV radiation

Composition/Structure of the Atmosphere

Focus Question What is all that matter above our heads in which we live and depend?

VA SOL SOL 2 (Infused) The student will demonstrate scientific reasoning and logic by a. analyzing how science explains and predicts the interactions and dynamics of complex Earth systems; and SOL 12 The student will investigate and understand the origin and evolution of the atmosphere and the interrelationship of geologic processes, biologic processes, and human activities on its composition and dynamics. Key concepts include

Composition of the Atmosphere The atmosphere and especially the air we breathe is a delicately balanced mixture of many gasses; but mostly nitrogen and oxygen. If either of these two were to change significantly life as we know it could not exist.

Composition of the Atmosphere The Earth s atmosphere is 21% oxygen, 78% nitrogen, and 1% trace gasses; argon, CO2, and water vapor are the most abundant The amounts of CO2 and water vapor vary significantly The water vapor levels can be as much as 4% or as little as almost 0% depending on the season and area

Composition of the Atmosphere CO2 and water vapor levels are critical to our survival because they regulate the amount of energy the atmosphere can absorb

Composition of the Atmosphere Water in the atmosphere stores and releases heat when it changes from one state to another causing the weather

Composition of the Atmosphere CO2 is responsible for the greenhouse effect where light energy from the Sun is reflected back into the atmosphere as infrared energy causing heat to accumulate. Too much CO2 is strongly believed to be the cause of global warming trends

Structure of the Atmosphere There are four main layers of the Earth s atmosphere. These layers are not rigidly defined by any certain altitude. Their boundaries are defined by altitude levels where the temperature trends reverse

Structure of the Atmosphere Troposphere is the lowest layer. It is the densest layer and is the layer in which most of the clouds and all weather occurs The temperature decreases as altitude increases

Structure of the Atmosphere The tropopause defines the upper boundary and varies from about 16 km at the tropics to 9 km at the poles

Structure of the Atmosphere Stratosphere is the next layer and begins above the tropopause. It is made of primarily concentrated ozone The temperature increases as altitude increases The stratopause defines the upper boundary and is located about 50 km above Earth s surface

Mesosphere Mesosphere is the third layer from the bottom and the temperature again decreases with altitude The mesopause is the upper boundary at about 80 km

Thermosphere Thermosphere is the highest layer but only contains a minute portion of the overall atmospheric mass. The temperature again increases with altitude to more than 1000 degrees C. The thermosphere also contains the ionosphere

Atmospheric Energy Transfer Space is a very cold place, yet the surface of the Earth is quite warm and comfortable. How does the energy from our Sun get converted to the useable forms that support life here?

Radiation Radiation is the transfer of energy through space by electromagnetic waves (UV, visible, infrared, gamma) Earth absorbs solar radiation, but also sends just about the same amount of energy back into space

Conduction Conduction is the transfer of energy by direct contact such as when a pot water is placed on a stove burner. Heat energy is transferred from the burner to the bottom of the pot then from the pot to the water. Little of our atmospheric processes involve conduction

Convection Convection is the transfer of energy through the flow of a heated substance (air, water, rock)

Convection As pockets of air at the Earth s surface are heated they become less dense than the surrounding air and rise

Convection As the air rises it begins to expand and cool to where it is cooler than the surrounding air then sinks again

Convection This ongoing process primarily responsible for the many changes we see in our weather throughout the year as air warms, cools, rises and falls as heat energy is either gained or lost

Convection