What Was The Earth's Atmosper Makeup During The Paleogene Period

Evolution of the Atmosphere: Composition, Construction and Free energy

I inhale smashing draughts of infinite,
The east and west are mine, and the due north and the south are mine
I am larger, better than I thought,
I did non know I held so much goodness - all seems cute to me.

- Song of the Open Route, Walt Whitman

Introduction To Global Change I Lecture Notes			Format for Printing
Early Temper, Oceans, and Continents	Composition of the Atmosphere	Evolution of the Atmosphere	Summary

Driving Questions:

• How did the atmosphere evolve into what it is today?
• What gases in the atmosphere are important to life and how are they maintained?
• What natural variations occur in atmospheric constituents and what are the important time scales for change?
  

1. The Earliest Atmosphere, Oceans, and Continents

After loss of the hydrogen, helium and other hydrogen-containing gases from early on World due to the Sun'southward radiation, archaic Globe was devoid of an atmosphere. The outset temper was formed by outgassing of gases trapped in the interior of the early Earth, which still goes on today in volcanoes.

For the Early on Earth, extreme volcanism occurred during differentiation, when massive heating and fluid-like move in the mantle occurred. It is likely that the majority of the temper was derived from degassing early in the Earth's history. The gases emitted by volcanoes today are in Table 1 and in Effigy.

Oxygen in the Atmosphere

Life started to have a major bear on on the environment once photosynthetic organisms evolved. These organisms, bluish-green algae (picture show of stromatolite, which is the rock formed past these algae), fed off atmospheric carbon dioxide and converted much of it into marine sediments consisting of the shells of sea creatures.

While photosynthetic life reduced the carbon dioxide content of the atmosphere, information technology also started to produce oxygen. For a long time, the oxygen produced did not build upwards in the atmosphere, since it was taken up past rocks, equally recorded in Banded Iron Formations (BIFs; flick) and continental cherry-red beds. To this day, the majority of oxygen produced over time is locked up in the aboriginal "banded rock" and "red bed" formations. It was not until probably but 1 billion years ago that the reservoirs of oxidizable rock became saturated and the free oxygen stayed in the air.

The oxidation of the the pall rocks may have played an important role in the ascension of oxygen. It has been hypothesized the the change from predominantly submarine to subaerial volcanoes may have also led to a reduction in volcanic emission of reduced gases.

In one case oxygen had been produced, ultraviolet low-cal split the molecules, producing the ozone UV shield equally a by-production. Only at this point did life motion out of the oceans and respiration evolved. We will discuss these issues in greater detail later on in this course.

Early on Oceans

The Early on atmosphere was probably dominated at kickoff past water vapor, which, every bit the temperature dropped, would rain out and grade the oceans. This would accept been a deluge of truly global proportions an resulted in further reduction of CO2. Then the temper was dominated by nitrogen, only at that place was certainly no oxygen in the early atmosphere. The dominance of Banded-Atomic number 26 Formations (BIFs; see picture) earlier 2.5Ga indicates that Iron occurred in its reduced state (Fe2+). Whereas reduced Atomic number 26 is much more than soluble than oxidized Fe (Fe3+), it chop-chop oxidizes during ship. Notwithstanding, the dissolved O in early oceans reacted with Atomic number 26 to form Iron-oxide in BIFs. As soon as sufficient O entered the atmosphere, Fe takes the oxidized state and is no longer soluble. The get-go occurrence of redbeds, a sediments that contains oxidized fe, marks this major transition in Globe's temper.

Early Continents

Lava flowing from the partially molten interior spread over the surface and solidified to form a sparse chaff. This crust would have melted and solidified repeatedly, with the lighter compounds moving to the surface. This is called differentiation.  Weathering past rainfall broke up and contradistinct the rocks.  The end issue of these processes was a continental country mass, which would have grown over time. The most pop theory limits the growth of continents to the first two billion years of the Earth.

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two. Development of the Present Atmosphere

The development of the atmosphere could be divided into four separate stages:

1. Origin
2. Chemical/ pre-biological era
3. Microbial era, and
4. Biological era.

and the commencement three steps were discussed in detail. The composition of the nowadays atmosphere even so required the germination of oxygen to sufficient levels to sustain life, and required life to create the sufficient levels of oxygen. This era of evolution of the atmosphere is called the "Biological Era."

The Biological Era - The Formation of Atmospheric Oxygen

The biological era was marked past the simultaneous decrease in atmospheric carbon dioxide (CO₂) and the increase in oxygen (O₂) due to life processes. Nosotros need to understand how photosynthesis could have led to maintenance of the ~20% present-day level of O_ii. The build upwardly of oxygen had three major consequences that we should note here.

Firstly, Eukaryotic metabolism could only have begun once the level of oxygen had built upward to near 0.2%, or ~one% of its present affluence. This must have occurred by ~ii billion years agone, according to the fossil record. Thus, the eukaryotes came nearly as a consequence of the long, steady, but less efficient before photosynthesis carried out by Prokaryotes.

Figure ane. Photolysis of water vapor and carbon dioxide produce hydroxyl and atomic oxygen, respectively, that, in plough, produce oxygen in small concentrations. This process produced oxygen for the early atmosphere before photosynthesis became ascendant.

Oxygen increased in stages, outset through photolysis (Figure i) of h2o vapor and carbon dioxide by ultraviolet energy and, peradventure, lightning:

H₂O -> H + OH

produces a hydroxyl radiacal (OH) and

CO₂ -> CO+ O

produces an atomic oxygen (O). The OH is very reactive and combines with the O

O + OH -> O_two + H

The hydrogen atoms formed in these reactions are calorie-free and some pocket-sized fraction excape to infinite allowing the O2 to build to a very depression concentration, probably yielded only about i% of the oxygen available today.

Secondly, once sufficient oxygen had accumulated in the stratosphere, it was acted on by sunlight to course ozone, which allowed colonization of the country. The first testify for tracheophyte colonization of the state dates back to ~400 million years ago.

Thirdly, the availability of oxygen enabled a diversification of metabolic pathways, leading to a great increment in efficiency. The majority of the oxygen formed once life began on the planet, principally through the process of photosynthesis:

6CO₂ + 6H₂O <--> C_half-dozenH₁₂O_six + 6O_ii

where carbon dioxide and h2o vapor, in the presence of light, produce organics and oxygen. The reaction can go either way as in the instance of respiration or decay the organic matter takes up oxygen to grade carbon dioxide and water vapor.

Life started to have a major touch on on the environment in one case photosynthetic organisms evolved. These organisms fed off atmospheric carbon dioxide and converted much of information technology into marine sediments consisting of the innumerable shells and decomposed remnants of sea creatures.

Cumulative history of O2 by photosynthesis through geologic time.

While photosynthetic life reduced the carbon dioxide content of the atmosphere, it as well started to produce oxygen. The oxygen did non build upwardly in the atmosphere for a long time, since it was absorbed by rocks that could be easily oxidized (rusted). To this mean solar day, most of the oxygen produced over time is locked upwardly in the ancient "banded stone" and "red bed" stone formations constitute in ancient sedimentary rock. It was non until ~ane billion years agone that the reservoirs of oxidizable stone became saturated and the gratuitous oxygen stayed in the air.  The effigy illustrates a possible scenario.

We have briefly mentioned the deviation between reducing (electron-rich) and oxidizing (electron hungry) substances. Oxygen is the virtually important case of the latter type of substance that led to the term oxidation for the procedure of transferring electrons from reducing to oxidizing materials. This consideration is important for our word of atmospheric evolution, since the oxygen produced past early on photosynthesis must take readily combined with any available reducing substance. It did non have far to await!

Nosotros accept been able to outline the steps in the long drawn out process of producing present-twenty-four hours levels of oxygen in the temper. Nosotros refer here to the geological evidence.

Banded Atomic number 26 Formations

When the oceans first formed, the waters must have dissolved enormous quantities of reducing atomic number 26 ions, such as Atomic number 26²⁺. These ferrous ions were the consequences of millions of years of rock weathering in an anaerobic (oxygen-free) environment. The first oxygen produced in the oceans by the early prokaryotic cells would take rapidly been taken up in oxidizing reactions with dissolved iron. This oceanic oxidization reaction produces Ferric oxide Fe_iiO₃ that would have deposited in sea floor sediments. The earliest evidence of this process dates back to the Banded Iron Formations, which reach a elevation occurrence in metamorphosed sedimentary stone at least 3.five billion years old. Most of the major economical deposits of atomic number 26 ore are from Banded Iron formations. These formations, were created as sediments in aboriginal oceans and are found in rocks in the range 2 - 3.5 billion years old. Very few banded fe formations accept been found with more recent dates, suggesting that the connected product of oxygen had finally wearied the adequacy of the dissolved iron ions reservoir. At this point another process started to have upwards the bachelor oxygen.

Scarlet Beds

Once the ocean reservoir had been exhausted, the newly created oxygen constitute another large reservoir - reduced minerals bachelor on the barren state. Oxidization of reduced minerals, such every bit pyrite FeS₂ , exposed on land would transfer oxidized substances to rivers and out to the oceans via river menstruation. Deposits of Fe₂O₃ that are found in alternating layers with other sediments of country origin are known as Ruby Beds, and are found to appointment from 2.0 billion years agone. The earliest occurrence of red beds is roughly simultaneous with the disappearance of the banded iron germination, further evidence that the oceans were cleared of reduced metals before O₂ began to diffuse into the temper.

Finally afterward another 1.5 billion years or so, the red bed reservoir became exhausted also (although it is continually being regenerated through weathering) and oxygen finally started to accumulate in the temper itself. This signal result initiated eukaryotic cell development, land colonization, and species diversification. Perhaps this flow rivals differentiation as the nigh of import outcome in World history.

The oxygen congenital up to today'south value just after the colonization of land by green plants, leading to efficient and ubiquitous photosynthesis. The current level of xx% seems stable.

The Oxygen Concentration Trouble.

Why does present-day oxygen sit at 20%? This is non a trivial question since significantly lower or higher levels would be damaging to life. If we had < 15% oxygen, fires would non fire, still at > 25% oxygen, even moisture organic matter would burn freely.

The Early Ultraviolet Trouble

The genetic materials of cells (Dna) is highly susceptible to harm by ultraviolet lite at wavelengths near 0.25 µm. It is estimated that typical gimmicky microorganisms would be killed in a matter of seconds if exposed to the full intensity of solar radiation at these wavelength. Today, of form, such organisms are protected past the atmospheric ozone layer that finer absorbs light at these brusque wavelengths, but what happened in the early Earth prior to the significant production of atmospheric oxygen? There is no trouble for the original non-photosynthetic microorganisms that could quite happily accept lived in the deep body of water and in muds, well hidden from sunlight. Merely for the early photosynthetic prokaryotes, it must have been a matter of life and decease.

Information technology is a classical "chicken and egg" problem. In order to become photosynthetic, early microorganisms must take had access to sunlight, yet they must accept also had protection confronting the UV radiation. The oceans only provide express protection. Since water does not absorb very strongly in the ultraviolet a depth of several tens of meters is needed for full UV protection. Peradventure the organisms used a protective layer of the expressionless bodies of their brethren. Perhaps this is the origin of the stromatolites - algal mats that would have provided adequate protection for those organisms buried a few millimeters in. Mayhap the early organisms had a protective UV-absorbing case made upwards of disposable Dna - there is some intriguing evidence of unused mod elaborate repair mechanisms that permit certain cells to repair moderate UV damage to their Deoxyribonucleic acid. Nonetheless it was achieved, we know that natural choice worked in favor of the photosynthetic microorganisms, leading to farther diversification.

Fluctuations in Oxygen

The history of macroscopic life on Earth is divided into three great eras: the Paleozoic, Mesozoic and Cenozoic. Each era is then divided into periods. The latter one-half of the Paleozoic era, includes the Devonian period, which ended about 360 one thousand thousand years ago, the Carboniferous period, which ended about 280 meg years ago, and the Permian menstruation, which ended about 250 million years agone.

According to recently developed geochemical models, oxygen levels are believed to have climbed to a maximum of 35 percentage and and then dropped to a depression of 15 per centum during a 120-million-year period that concluded in a mass extinction at the end of the Permian. Such a jump in oxygen would have had dramatic biological consequences by enhancing diffusion-dependent processes such as respiration, allowing insects such as dragonflies, centipedes, scorpions and spiders to grow to very large sizes. Fossil records indicate, for example, that one species of dragonfly had a wing bridge of 2 1/2 feet.

Geochemical models point that near the close of the Paleozoic era, during the Permian menses, global atmospheric oxygen levels dropped to about fifteen percent, lower that the electric current atmospheric level of 21 percent. The Permian catamenia is marked by one of the greatest extinctions of both land and aquatic animals, including the giant dragonflies. Only it is not believed that the drop in oxygen played a meaning role in causing the extinction. Some creatures that became specially adjusted to living in an oxygen-rich environs, such as the large flying insects and other giant arthropods, however, may have been unable to survive when the oxygen atmosphere underwent dramatic change.

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3. Limerick of the Nowadays Temper

Comparison to Other Planets

The overall composition of the earth's atmosphere is summarized below forth with a comparison to the atmospheres on Venus and Mars - our closest neighbors.

	VENUS	Globe	MARS
SURFACE Pressure	100,000 mb	one,000 mb	6 mb
	Composition
CO2	>98%	0.03%	96%
N2	1%	78%	two.v%
Ar	ane%	ane%	ane.5%
O2	0.0%	21%	2.5%
H2O	0.0%	0.1%	0-0.one%
	(more on Mars)	(more on Earth)	(more on Mars)

The variations in concentration from the Earth to Mars and Venus outcome from the different processes that influenced the evolution of each temper. While Venus is as well warm and Mars is too cold for liquid water the Earth is at just such a altitude from the Dominicus that h2o was able to class in all three phases, gaseous, liquid and solid. Through condensation the water vapor in our temper was removed over time to course the oceans. Additionally, because carbon dioxide is slightly soluble in water it also was removed slowly from the temper leaving the relatively scarce simply unreactive nitrogen to build upward to the 78% is holds today.

Current Composition

The unit of percentage listed hither are for comparing sake. For most atmospheric studies the concentration is expressed every bit parts per 1000000 (by volume). That is, in a million units of air how may units would exist that species. Carbon dioxide has a concentration of about 350 ppm in the temper (i.due east. 0.000350 of the temper or 0.0350 percent).

Greenhouse Gases

Click to interactively explore Selective Absorbers.

Radiative Backdrop

Objects that absorb all radiation incident upon them are called "blackbody" absorbers. The earth is close to being a blackness body cushion. Gases, on the other hand, are selective in their absorption characteristics. While many gases practice not absorb radiations at all some selectively absorb only at certain wavelengths. Those gases that are "selective absorbers" of solar energy are the gases we know as "Greenhouse Gases."

The interactive activity to the right allows you to visualize how each greenhouse gas selectively absorbs radiations. Wien's Police states that the wavelength of maximum emission of radiation is inversely proportional to the object's temperature. Using that law we know that the wavelength of maximum emission for the Sun is near 0.five µm (1 µm = 10^{-half dozen} m) and the wavelength for maximum emission by the Earth is about 10 µm. In the activity to the right see where the greenhouse gases absorb relative to those two important wavelengths.

Sources and Sinks

Greenhouse Gases (autonomously from water vapor) include:

• Carbon Dioxide
• Chlorofluorocarbons (CFCs)
• Methane
• Nitrous Oxide
• Ozone

and each have different sources (emission mechanisms) and sinks (removal mechanisms) equally outlined below.

	Carbon Dioxide
Sources	Released by the combustion of fossil fuels (oil, coal, and natural gas), flaring of natural gas, changes in land apply (deforestation, burning and clearing land for agronomical purposes), and manufacturing of cement
Sinks	Photosynthesis and deposition to the ocean.
Importance	Accounts for about one-half of all warming potential caused by man activity.

	Methane
Sources	Landfills, wetlands and bogs, domestic livestock, coal mining, moisture rice growing, natural gas pipeline leaks, biomass burning, and termites.
Sinks	Chemic reactions in the atmosphere.
Importance	Molecule for molecule, methane traps heat 20-30 times more efficiently than COii. Within l years it could become the virtually significant greenhouse gas.

	Nitrous Oxide
Sources	Burning of coal and wood, likewise equally soil microbes' digestion..
Sinks	Chemic reactions in the atmosphere.
Importance	Long-lasting gas that somewhen reaches the stratosphere where it participates in ozone destruction.

Sources	Ozone
Sources	Non emitted directly, ozone is formed in the atmosphere through photochemical reactions involving nitrogen oxides and hydrocarbons in the presence of sunlight.
Sinks	Deposition to the surface, chemical reactions in the temper.
Importance	In the troposphere ozone is a pollutant. In the stratosphere it absorbs hazardous ultraviolet radiation.

	Chlorofluorocarbons (CFCs)
Sources	Used for many years in refrigerators, automobile air conditioners, solvents, aerosol propellants and insulation.
Sinks	Degradation occurs in the upper atmosphere at the expenses of the ozone layer. 1 CFC molecule can initiate the devastation of equally many as 100,000 ozone molecules.
Importance	The most powerful of greenhouse gases — in the atmosphere one molecule of CFC has about 20,000 times the heat trapping power on a molecule of CO2.

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4. Summary

Nosotros developed a few useful tools for the study of biogeochemical cycles. These include the concepts of the reservoir, fluxes, and equilibria.

• Atmospheric evolution progressed in four stages, leading to the current situation. The atmosphere has not ever been as it is today - and it will change again in the time to come. It is closely controlled by life and, in turn, controls life processes. Circuitous feedback mechanisms are at play that nosotros do not yet sympathize.
• Oxygen became a key atmospheric constituent due entirely to life processes. It built upward slowly over fourth dimension, first oxidizing materials in the oceans and then on state. The current level (xx%) is maintained by processes not withal understood.
• Sometime only before the Cambrian, atmospheric oxygen reached levels close enough to today's to permit for the rapid evolution of the higher life forms. For the rest of geologic time, the oxygen in the atmosphere has been maintained by the photosynthesis of the dark-green plants of the world, much of it by green algae in the surface waters of the ocean.
• Selective absorbers in our atmosphere continue the surface of the earth warmer than they would be without an atmosphere.

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Source: https://globalchange.umich.edu/globalchange1/current/lectures/deep_time/index.html

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