CSET Requirement: 2.3b: Discuss the evolution of Earth’s atmosphere over geologic time, including the effects of outgassing, the variations of carbon dioxide concentration, and the origin of atmospheric oxygen.
Outgassing
When Earth's first atmosphere was formed, it may have consisted primarily of hydrogen, and helium (the two most abundant gases in the universe). Through the process of outgassing (outpouring of gases from Earth's interior), methane, ammonia, carbon dioxide, and water vapors were introduced into the atmosphere. There was no free oxygen in the atmosphere yet. Hydrogen and helium gases probably escaped into the space early due to the fact that these gases were too light to be held onto by Earth's gravity. Many of the other gases may have been blown off of earth by solar winds from the young and active star: our sun.
Outgassing occurs when gases are trapped in a planet and released into the atmosphere. This outgassing is still occurring today through volcanic activities and eruptions. Gases emitted today are probably similar to the ones emitted in Earth's early life. Gases emitted by volcanic activity includes 35-90 % water vapor, 5-30 % carbon dioxide, 2-30 % sulfur dioxide, and trace amounts of nitrogen, chlorine, hydrogen, and argon. Thus, the early atmosphere must have consisted primarily of water vapor, carbon dioxide, and sulfur dioxide, with trace amounts of the other gases.
ORIGINS OF ATMOSPHERIC OXYGEN
Life started to have a major impact on the environment once photosynthetic organisms evolved. These organisms, blue-green algae, fed off atmospheric carbon dioxide and converted much of it into marine sediments consisting of the shells of sea creatures (cephalopods).
While photosynthetic life reduced the carbon dioxide content of the atmosphere, it also started to produce oxygen. For a long time, the oxygen produced did not build up in the atmosphere, since it was taken up by rocks. Oxygen readily joined up with iron to form iron oxide. To this day, the majority of oxygen produced over time is locked up in the ancient "banded rock" and "red bed" formations. It was not until probably only 1 billion years ago that the reservoirs of oxidizable rock became saturated and the free oxygen stayed in the air.
Oxygen could have been found in the atmosphere as early as 2.45 bya. The amount of oxygen slowly increased and became stable at around 1.5 bya. Eventually, as the oxygen molecules were bombarded by ultraviolet radiation, it formed ozone, which eventually formed the ozone layer (which helped to protect earth from solar radiation for the first time ever). Only at this point did life move out of the oceans and respiration evolved.
Outgassing occurs when gases are trapped in a planet and released into the atmosphere. This outgassing is still occurring today through volcanic activities and eruptions. Gases emitted today are probably similar to the ones emitted in Earth's early life. Gases emitted by volcanic activity includes 35-90 % water vapor, 5-30 % carbon dioxide, 2-30 % sulfur dioxide, and trace amounts of nitrogen, chlorine, hydrogen, and argon. Thus, the early atmosphere must have consisted primarily of water vapor, carbon dioxide, and sulfur dioxide, with trace amounts of the other gases.
ORIGINS OF ATMOSPHERIC OXYGEN
Life started to have a major impact on the environment once photosynthetic organisms evolved. These organisms, blue-green algae, fed off atmospheric carbon dioxide and converted much of it into marine sediments consisting of the shells of sea creatures (cephalopods).
While photosynthetic life reduced the carbon dioxide content of the atmosphere, it also started to produce oxygen. For a long time, the oxygen produced did not build up in the atmosphere, since it was taken up by rocks. Oxygen readily joined up with iron to form iron oxide. To this day, the majority of oxygen produced over time is locked up in the ancient "banded rock" and "red bed" formations. It was not until probably only 1 billion years ago that the reservoirs of oxidizable rock became saturated and the free oxygen stayed in the air.
Oxygen could have been found in the atmosphere as early as 2.45 bya. The amount of oxygen slowly increased and became stable at around 1.5 bya. Eventually, as the oxygen molecules were bombarded by ultraviolet radiation, it formed ozone, which eventually formed the ozone layer (which helped to protect earth from solar radiation for the first time ever). Only at this point did life move out of the oceans and respiration evolved.
Variations of Carbon Dioxide (C02) concentration
The long-term evolution of carbon dioxide levels depend on weathering and magmatism, the relative fluctuations of CO2 levels are inferred from fluctuations of the isotopic (concentration of elements) records.
Five hundred million years ago carbon dioxide was 20 times more prevalent than today, decreasing to 4–5 times during the Jurassic period and then slowly declining with a particular swift reduction occurring 49 million years ago. Human activities such as the combustion of fossil fuels and deforestation have caused the atmospheric concentration of carbon dioxide to increase by about 35% since the beginning of the age of the industrial era. Emissions of CO2 by human activities are estimated to be 135 times greater than the quantity emitted by volcanoes. Up to 40% of the gas emitted by some volcanoes during eruptions is carbon dioxide. It is estimated that volcanoes release about 130–230 million tonnes (145–255 million tons) of CO2 into the atmosphere each year.
Most scientists agree that carbon dioxide has decreased over the last 200 million years because of speeding up of the passage of carbon atoms from their volcanic sources into sediments. Fresh rocks are provided through plate collisions and mountain building, that is, uplift of land and a drop in sea level. On the whole, there has been a trend to make more mountains during the last 100 million years, and especially since the last 40 million years. This is seen in the strontium isotope content of marine carbonates. The type of strontium derived from igneous rocks on land has increased relative to the type of strontium from other sources.
Organic matter is buried in swamps (plant remains turn into coal) and in continental margins (marine remains become hydrocarbons). The climate cooled as the planet acquired mountain ranges (like the Himalayas) and as sea level dropped. Trade winds became more vigorous. Coastal upwelling of nutrients in coastal waters increased. Thus, more organic matter was buried along the coasts of continents. Also, an increase in the amount of mud from the rising mountains helped to bury the organic matter. As time went on carbon dioxide was more readily turned into sedimentary carbon and the planet cooled some more.
Looking at the picture above, you will see that there was a period in geologic history where carbon dioxide and temperature were similar to today's atmosphere. This notable exception is 300 million years ago during the late Carboniferous Period, which resembled our own climate and atmosphere like no other Earth's climate and atmosphere have varied greatly over geologic time. Our planet has mostly been much hotter and more humid than we know it to be today, and with far more carbon dioxide (the greenhouse gas) in the atmosphere than exists today. .
Five hundred million years ago carbon dioxide was 20 times more prevalent than today, decreasing to 4–5 times during the Jurassic period and then slowly declining with a particular swift reduction occurring 49 million years ago. Human activities such as the combustion of fossil fuels and deforestation have caused the atmospheric concentration of carbon dioxide to increase by about 35% since the beginning of the age of the industrial era. Emissions of CO2 by human activities are estimated to be 135 times greater than the quantity emitted by volcanoes. Up to 40% of the gas emitted by some volcanoes during eruptions is carbon dioxide. It is estimated that volcanoes release about 130–230 million tonnes (145–255 million tons) of CO2 into the atmosphere each year.
Most scientists agree that carbon dioxide has decreased over the last 200 million years because of speeding up of the passage of carbon atoms from their volcanic sources into sediments. Fresh rocks are provided through plate collisions and mountain building, that is, uplift of land and a drop in sea level. On the whole, there has been a trend to make more mountains during the last 100 million years, and especially since the last 40 million years. This is seen in the strontium isotope content of marine carbonates. The type of strontium derived from igneous rocks on land has increased relative to the type of strontium from other sources.
Organic matter is buried in swamps (plant remains turn into coal) and in continental margins (marine remains become hydrocarbons). The climate cooled as the planet acquired mountain ranges (like the Himalayas) and as sea level dropped. Trade winds became more vigorous. Coastal upwelling of nutrients in coastal waters increased. Thus, more organic matter was buried along the coasts of continents. Also, an increase in the amount of mud from the rising mountains helped to bury the organic matter. As time went on carbon dioxide was more readily turned into sedimentary carbon and the planet cooled some more.
Looking at the picture above, you will see that there was a period in geologic history where carbon dioxide and temperature were similar to today's atmosphere. This notable exception is 300 million years ago during the late Carboniferous Period, which resembled our own climate and atmosphere like no other Earth's climate and atmosphere have varied greatly over geologic time. Our planet has mostly been much hotter and more humid than we know it to be today, and with far more carbon dioxide (the greenhouse gas) in the atmosphere than exists today. .