1. Earth and Space: Unit Three
(6)  Earth in space and time. The student knows the evidence for how Earth's atmospheres, hydrosphere, and geosphere formed and changed through time. The student is expected to:
(a)  analyze the changes of Earth's atmosphere that could have occurred through time from the original hydrogen-helium atmosphere, the carbon dioxide- water vapor-methane atmosphere, and the current nitrogen-oxygen atmosphere;
(b)  evaluate the role of volcanic outgassing and
impact of water-bearing comets in developing Earth's atmosphere and hydrosphere;

2. Basic working vocabulary
Atmosphere, Hydrosphere, and Geosphere
Basic working vocabulary
Atmosphere
Hydrosphere
Geosphere
The atmosphere is a layer of gases surrounding the planet that is held close to us by our gravitational field. It protects organisms by absorbing the relatively dangerous part of the EM spectrum known as ultraviolet radiation. The atmosphere helps keep the Earth’s surface warm through retention of thermal energy, which helps reduce temperature extremes between day and night.
The atmosphere is seen here as the blue haze above the planet
The hydrosphere describes the combined mass of water found on, under, and over the surface of a planet. It includes liquid water in the oceans, rivers, lakes, clouds, soil, and groundwater; solid water in snow and ice found in cold regions and in ice caps; gaseous water found in the atmosphere.
The geosphere includes the solid Earth portion of the Earth Systems. Rocks and soil (regolith) at the surface, and all the deep interior portions of the Earth. It differs from the Lithosphere, which only includes the planet’s crust and upper mantle.

3. Today’s Atmosphere Chemical Composition Today: Nitrogen (N2)- 78%,
Oxygen (O2)- 21%,
Trace Gases-Argon, CO2, H2O and others…

4. How’d We Get There? First Atmosphere’s 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 lighter gases could be retained
The Van Allen radiation belt is a field of energetically charged particles surrounding the Earth, which is held in place by Earth’s magnetic field. It is believed that most of the particles that form the belts come from solar wind, and other particles by cosmic rays. It is located in the inner region of the Earth's magnetosphere. It is split into two distinct belts, with energetic electrons forming the outer belt and a combination of protons and electrons forming the inner belts.

5. Second Atmosphere Origin and Composition:
Produced by volcanic out gassing.   Gases produced were probably similar to those created by modern volcanoes
(H2O, CO2, SO2, CO, S2, Cl2, N2, H2, NH3 (ammonia) and CH4 (methane)
No free O2 at this time (not found in volcanic gases).
Uniformitarianism
James Hutton introduced this geologic concept, which is a recurring theme in Earth and Space science.

6. How are the geosphere and the lithosphere different?
Why do scientists think the first atmospheric gases were H2 and He?
How would Earth’s first atmosphere get “lost” in space?
How was Earth’s 2nd atmosphere likely produced?
What gas was likely not present in Earth’s 2nd atmosphere?

7. Evidence - pillow basalts, deep marine beds in greenstone belts.
Pillow basalts are special rocks that are formed from lava flowing beneath the water. This last picture is of weathered Archean pillow lava in the greenstone belt in the Canadian Shield.
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 beds in greenstone belts.

8. The term Archean means “ancient” and was originally used to refer to the oldest known rocks. Rocks of Archean age contain the earliest fossils of life on Earth. Because these rocks were formed very long ago—between 2.5 to 4.0 billion years ago—most have long since been covered by younger sediments, eroded, or subducted into the Earth's mantle. Nevertheless, some Archean strata survived in the central parts of continents. These Archean “shields” lie in the heart of Canada, Australia, Africa, India, and Siberia.

9. No Oceans at the Beginning
The Earth in its earliest years was a horribly hot and violent place. Asteroids, comets, and other chunks of space debris left over from the solar system's formation continually bombarded the young planet, releasing huge amounts of heat.
The decay of radioactive elements inside the Earth also generated great quantities of heat. At the same time, frequent volcanic eruptions may have covered much of the planet's surface in red-hot flows of lava. The early Earth's surface was hot enough to turn any liquid water instantly into steam. Nonetheless, the planet eventually cooled enough and obtained enough water to fill a vast ocean.

10. Or…both? Comets, or Outgassing?
Some of the water in the Earth's oceans came from condensation following the outgassing of water vapor from volcanoes on the surface of the planet, while some was delivered by impacting comets. An important question in recent years has been the relative importance of these two sources.
As the Earth cooled to below 100oC oceans were formed when water vapor that was outgassed from volcanoes condensed and formed liquid water. Oceans are reservoirs for carbon dioxide because they can store the gas when it dissolves in  them.  The oceans are called carbon “sinks” as a result of their capacity to store carbon. The new oceans dissolved a great deal of the carbon dioxide in the atmosphere.  The oceans still play a part in keeping carbon dioxide levels constant.  If there is a lot of carbon dioxide in the air then more can dissolve.  If there is less carbon dioxide in the air then some comes out of solution back into the air. Now, aquatic plants and phytoplankton serve to recycle this dissolved CO2, and use it for photosynthetic purposes.
Or…both?

11. Evidence Shoemaker-Levy
According to one school of thought, comets may have supplied the bulk of oceanic water during the heavy bombardment phase of the solar system, between about 4.5 and 3.8 billion years ago.
Shoemaker-Levy
If this is true, it increases the chances that the delivery of organic matter, (also found in comets) played an important part in the origin of life on Earth.
However, cosmochemists found that comet Hale-Bopp contains substantial amounts of heavy water, which is rich in the hydrogen isotope deuterium.
If Hale-Bopp is typical in this respect and if cometary collisions were a major source of terrestrial oceans, it suggests that Earth's ocean water should be similarly rich in deuterium, whereas in fact it is not.
Comets that formed closer to Jupiter (short-period comets) in the Kuiper Belt, are more likely to contain earth-like water, while long-period comets forming in the Oort Cloud region are more than likely the ones that contain heavy water.
While studies suggest that most of Earth's water probably did not have a cometary origin, there is contradictory data as well. It is hotly debated to this day!

12. What evidence is there that there was water on the Earth during the early Archaen?
What evidence is there that water was delivered by comets?
What evidence is there that water was formed from volcanic outgassing?
Which theory has more evidence today?

13. The Great Oxidation Event
GOE
The Great Oxidation Event
Today, the atmosphere is 21% free oxygen. How did oxygen reach these levels in the atmosphere? Let’s look at processes that contribute to the cycling of O2 on our planet:
Oxygen Producers:
  Photochemical dissociation - breakup of water molecules by ultraviolet radiation
Produced O2 levels approx. 1-2% current levels
At these levels O3 (Ozone) can form to shield Earth surface from UV
Photosynthesis - CO2 + H2O C6H12O6+ O2
produced by cyanobacteria, and eventually higher plants – probably supplied the rest of O2 to atmosphere.
Oxygen Consumers
  Chemical Weathering - through oxidation of surface materials (early consumer)
Animal Respiration (much later)
Burning of Fossil Fuels (much, much later)
Sunlight

14. The Great Oxidation Event
GOE
The Great Oxidation Event
Today, the atmosphere is 21% free oxygen. How did oxygen reach these levels in the atmosphere? Let’s look at processes that contribute to the cycling of O2 on our planet:
Oxygen Producers:
  Photochemical dissociation - breakup of water molecules by ultraviolet radiation
Produced O2 levels approx. 1-2% current levels
At these levels O3 (Ozone) can form to shield Earth surface from UV
Photosynthesis - CO2 + H2O C6H12O6+ O2
produced by cyanobacteria, and eventually higher plants – probably supplied the rest of O2 to atmosphere.
Oxygen Consumers
  Chemical Weathering - through oxidation of surface materials (early consumer)
Animal Respiration (much later)
Burning of Fossil Fuels (much, much later)
Sunlight

15. Evidence Evidence from the Rock Record includes
Iron (Fe), which is 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 – minerals that only form in non-oxidizing environments in these sediments: Pyrite (Fools gold; FeS2), Uraninite (UO2). These minerals are easily dissolved out of rocks under present atmospheric conditions.
Banded Iron Formation (BIF) - Deep water deposits in which layers of iron-rich minerals alternate with iron-poor layers, primarily chert. These are common in rocks B.y. old, but do not form today.
Red beds are never found in rocks older than 2.3 B. y., but are common during later times. Red beds are red because of the highly oxidized mineral hematite (Fe2O3)
Conclusion – the amount of O2 in the atmosphere has increased with time.
Iron dissolves in water that has no oxygen. In the presence of oxygen, iron chemically reacts forming an insoluble iron oxide, which precipitates out of solution. In the organic model for BIF formation oxygen produced from the process of photosynthesis, carried out by cyanobacteria, accounts for the formation of the iron rich bands.

16. Banded Iron formations
no oxygen, iron is dark
Banded Iron formations
Lots of oxygen, iron is red
Iron dissolves in water that has no oxygen. In the presence of oxygen, iron chemically reacts forming an insoluble iron oxide, which precipitates out of solution. In the organic model for BIF formation oxygen produced from the process of photosynthesis, carried out by cyanobacteria, accounts for the formation of the iron rich bands.

17. What about the co2 and nitrogen?
The primordial atmosphere had 1,000 times more CO2 than it does now. Where did it all go?
H2O condensed to form the oceans.
CO2 dissolved into the oceans and precipitated out as carbonates (e.g., limestone).
Most of the present-day CO2 (the largest carbon sink) is locked up in crustal rocks and dissolved in the oceans.
By contrast, N2 is chemically inactive, and stayed a gas in the atmosphere and become its dominant constituent.

18. What about the co2 and nitrogen?
The primordial atmosphere had 1,000 times more CO2 than it does now. Where did it all go?
H2O condensed to form the oceans.
CO2 dissolved into the oceans and precipitated out as carbonates (e.g., limestone).
Most of the present-day CO2 (the largest carbon sink) is locked up in crustal rocks and dissolved in the oceans.
By contrast, N2 is chemically inactive, and stayed a gas in the atmosphere and become its dominant constituent.

19. How are BIFs and Red beds evidence of Earth’s oxygen atmosphere?
What are two oxygen producers?
What are two oxygen consumers?
Why is ozone important for the origin of life?
Where is the Earth’s largest carbon sink today?
Why is N2 the largest part of Earth’s atmosphere today?

20. Just a reminder…
The geosphere refers to everything from the core of the Earth to its surface.

21. The Biosphere
The biosphere is the layer of life on Earth. It exists beneath, upon, and above the surface in the atmosphere as well.
Axolotl
Harvestman
Airborne Bacteria
Soil Nematodes

22. What Role Did O2 Play?
One thing most geologists agree on is that the Earth’s first atmosphere contained no free oxygen. There were trace amounts of Oxygen bound in water molecules, and Carbon dioxide…but none of it was “free”, or molecular oxygen. (O2)

23. Let’s Review Photochemical Dissociaton
Photochemical Dissociation Hypothesis states that the sun’s energy helped the atmosphere evolve through the following processes:
The ultraviolet light combined with the water vapor to set the hydrogen off into space and free the oxygen. 2H2O + UV light energy ----> 2H2 (freed into space) + O2
The newly freed oxygen reacted with methane, forming carbon dioxide and additional water vapor. CH4 + 2O2 ----> CO2 + 2H2O
The oxygen also reacted with ammonia, producing nitrogen and water. 4NH3 + 3O2 ----> 2N2 + 6H2O
After converting the ammonia and methane to carbon dioxide and nitrogen, free oxygen began to accumulate as further dissociation of water vapor continued.

24. 3. What is meant by “free oxygen”?
Besides water, what other molecules play a huge role in photochemical dissociation?
What happens when freed oxygen combines with methane?
What happens when freed oxygen combines with ammonia?

25. Outgassing…
This theory states that our atmosphere was delivered to us from the Earth’s interior through volcanic eruptions. In contrast to the Photochemical Dissociation Hypothesis, the Outgassing Hypothesis argues that the free oxygen came from the photosynthesis of primitive organisms which existed billion years ago.
The oxygen took approximately 2 billion years to become free, but when it did, it formed the ozone layer, eliminating the dangerous radiation and setting up the foundation for a habitable planet.
UVA has a longer wavelength than UVB, and therefore is not filtered out as greatly, but it isn’t as harmful as UVB either. Without this protective ozone layer (O3), life would not have evolved.

26. Outgassing…
This theory states that our atmosphere was delivered to us from the Earth’s interior through volcanic eruptions. In contrast to the Photochemical Dissociation Hypothesis, the Outgassing Hypothesis argues that the free oxygen came from the photosynthesis of primitive organisms which existed billion years ago.
The oxygen took approximately 2 billion years to become free, but when it did, it formed the ozone layer, eliminating the dangerous radiation and setting up the foundation for a habitable planet.
UVA has a longer wavelength than UVB, and therefore is not filtered out as greatly, but it isn’t as harmful as UVB either. Without this protective ozone layer (O3), life would not have evolved.

27. Either Way…
It is obvious that Earth contains O2 now, and without it, aerobic life would not be possible.
What life could have evolved all those billions of years ago, before there was significant O2 in our atmosphere?
Anaerobic life forms
Watch the short video about anaerobic life on Earth:

28. Although the early Earth was mostly devoid of molecular oxygen, high volcanic activity released significant amounts of molecular hydrogen.
With little oxygen available to convert that hydrogen into water, hydrogen gas probably accumulated in the atmosphere and oceans in concentrations as high as hundreds to thousands of parts per million.
Thus, the early Earth was likely a paradise for methanogens (methane-producing bacteria) that fed directly on hydrogen and carbon dioxide, at least until the atmospheric hydrogen was depleted.
Early Life
Ask students how the first atmosphere became depleted again…solar wind blew it away, as the Earth hadn’t fully differentiated yet, the gravitational attraction pulling our atmosphere to us today was not present, along with the Van Allen belts (magnetosphere) which protects us from these solar winds.

29. Banded Iron Formations
Many anaerobic microbes including methanogens are easily poisoned by oxygen, and the recent discovery of banded sediments with rusted iron suggests that oxygen-producing, photosynthetic microbes called cyanobacteria were able to gather sunlight for photosynthesis. These BIFs would not have formed without O2 present in the atmosphere.
The evolution of O2 in our atmosphere spelled doom for the proliferate methanogens, and other types of extremophiles that had evolved during this early period in Earth’s past.
The layers indicate a time when oxygen was so scarce in the atmosphere that scientists think it was “used up”, perhaps seasonally, being consumed by reacting with the iron in the water, and then precipitating out in the rusty sediments that appear red in color. The other sediments formed when the oxygen was again gone. Soon, however, the photosynthetic organisms began pumping so much oxygen into the sediments that this rock formation could no longer happen. This is evidence that free oxygen was available in the atmosphere. Because the ocean is now oxygenated, iron cannot dissolve in sea water anymore. It precipitates out as iron oxide (rust).

30. Importance of Cyanobacteria
Despite their small stature, one of the first aerobic organisms (require the presence of O2) set in motion a process that would change everything.
These cyanobacteria which evolved billion years ago (also known as blue-green algae), were remarkably self-sufficient creatures that could use the sun’s energy to make their own food, and fix nitrogen, a process where nitrogen gas is converted into ammonia or nitrate. (NH3; NO3)
While this may not seem significant, the cycling of nitrogen on Earth is essential for life. It is found in amino acids, proteins, and genetic material. Nitrogen is the most abundant element in the atmosphere (~78%). However, gaseous nitrogen must be 'fixed' into another form so that it can be used by living organisms.

31. What primitive organism uses photosynthesis to combine CO2 and water in the presence of sunlight to make sugar and O2?
What are methanogens, and why was early Earth a paradise for them?
Where did these methanogens retreat to, when oxygen started evolving in our atmosphere?
Where did the molecular hydrogen of the Earth’s first atmosphere likely go?
How do are banded iron formations created…and why can’t they form anymore?

32. The Next 2 Billion Years…
And then...nothing else happened. At least, not for another two billion years.
It wouldn't be until about 600 million years ago, that the first multicellular organisms finally emerged.
So what happened during that immense, multi-billion year gap? Why did it take so long for more complex life to arrive on the scene?
The simple, uncomfortable answer is that we don't really know.
But that doesn’t keep geochemists from hypothesizing!
For that matter, why did oxygen suddenly spike 2.5 billion years ago?
???

33. Cooling Earth Theory
We already know that over time, the Earth’s crust cooled. The crust is thin, relatively, varying from a few tens of kilometers thick beneath the continents to less than 10 km thick beneath the oceans.
The crust and upper mantle together constitute the lithosphere, which is typically km thick and is broken into large plates. These plates sit on the asthenosphere.
The asthenosphere is kept plastic largely through heat generated by radioactive decay. This heat source is relatively small, but nevertheless, because of the insulating properties of the Earth's rocks at the surface, this is sufficient to keep the asthenosphere plastic in consistency.
One kilometer is .6 miles (to help give some reference)

34. 13. Why was there a huge 2 billion year gap between the first origins of life and oxygen in the atmosphere, and the appearance of more complex life forms?
14. What is the lithosphere composed of, and what does it sit on top of?
15. What keeps the asthenosphere plastic?

35. Convection Currents Energy can be transferred in three ways… Radiation
Conduction
Convection
Very slow convection currents flow in the asthenosphere, (upper portion of the mantle) and these currents provide horizontal forces on the plates of the lithosphere much as convection in a pan of boiling water causes a piece of cork on the surface of the water to be pushed sideways
Energy transfer across the vacuum of space
Energy transfer directly from molecule to molecule (solids)
Energy transfer through fluids (liquids and gases)

37. 16. Give an example of how Earth experiences the transferal of thermal energy in the form of radiation.
17. Give an example of conduction of thermal energy.
Give an example of convection of thermal energy.
In what media does each type of thermal energy transfer?

38. Plate Tectonics over time…
Of course, the timescale for convection in the pan is seconds and for plate tectonics is million years, but the principles are similar.
Differentiation within the Earth is crucial to plate tectonics, because it is responsible for producing an interior that can support tectonic motion.
The heat generated by the lower mantle, drives the convection currents upward against the lithospheric plates. As the currents cool, they move laterally, pushing and pulling the lithosphere apart. Then, the currents move downward again, where they begin to heat up once more due to proximity to lower mantle heat.

39. Influence of the Geosphere…
While seemingly static, the geosphere is in fact a very active player in the Earth systems, affecting the atmosphere and the hydrosphere, as well as critical processes such as the hydrologic cycle and other biogeochemical cycles.
The types of minerals contained in soils--a factor of geologic processes--help to determine the vegetative cover and ecosystems at the surface.
Carbon – an essential element of life – is bound in organic matter and is carried to the ocean via wind and water erosion where eventually it becomes part of the ocean floor.

40. Influence of the Geosphere…
The bedrock layer beneath this soil profile (Parent material) will determine the minerals that are dissolved within the soil, which will influence what types of vegetation will grow there.
The last picture is the Mississippi River Delta. You can see all the sediment (Carbon-rich) being deposited into the delta region.

41. 20. How does the geosphere influence the biosphere?
21. How does the geosphere influence the hydrosphere?
Why has the differentiation of the Earth been so important a factor in tectonic movement?

42. So What?
Tectonic movement carries the ocean deposits into the Earth's interior. On geologic timescales, volcanic activity can vent the carbon to the Earth's atmosphere as carbon dioxide.
The carbon cycle is one of the key cycles linking the Earth’s subsystems: geosphere, atmosphere, hydrosphere, and biosphere.
The outer core of the Earth contains liquid iron. Its motion is thought to drive the Earth's magnetic field – the magnetosphere - which extends far beyond the atmosphere protecting Earth and its biosphere from solar wind and cosmic radiation.

43. So What?

44. Evolving Continents
Link of animation of Pangea to current continents (last 200,000,000 years) Click small globe to watch animation.
Being dynamic, the Earth is still changing. 150 million years in the future, the continents should look something like this.
In 250 million years, we will have another Pangea supercontinent.