Activity 3

Question 1

Earth and Venus are similar in several ways: HOW?

Habitable zones + size

Answer 1

• Both considered to be within the potentially habitable zone of their star (Venus at 108 million km and Earth at 148 million km from the sun).
• They are also similar in size

Question 2

What is a system? How do they work?

Answer 2

• A system is any part of the universe, at any scale, that can be “isolated” and studied.
• Systems operate on many interconnected scales; for example, an atom is a system of protons, neutrons, and electrons.

Question 3

The Earth has four main systems

Answer 3

1. Geosphere
2. Hydrosphere
3. Atmosphere
4. Biosphere

Question 4

Two sub-systems of earth

Answer 4

1. The Cryosphere
2. The Anthrosphere

Question 5

The Cryosphere

Answer 5

a subdivision of the hydrosphere that includes all parts of the Earth where water is solid, including sea and lake ice, ice sheets and caps, glaciers, snow, and frozen ground (permafrost)

Question 6

The Anthrosphere:

Answer 6

• a part of the biosphere that includes humans and all their activities.
• Homo sapiens sapiens (modern humans) probably evolved around 200 000 years ago but have only relatively recently started to have a significant impact on the other Earth systems

Question 7

Feedback can be defined as:

System Feedback Interactions

Answer 7

…how the output from one system serves as input to another system, resulting in a change in that system’s state

Question 8

Two types of feedback can be recognized:

System Feedback Interactions

Answer 8

negative and positive

Question 9

Negative Feedback

Answer 9

Negative feedback moves the system in the OPPOSITE direction of the stimulus and generally helps maintain a steady state in a system or HOMEOSTASIS.

Question 10

What is the primary effect of homeostasis?

Answer 10

…to STABILIZE a system in a PREDICTABLE manner

Question 11

Earth example of negative feedback: the regulation of CO2

Answer 11

• Shortwave radiation from the sun passes through the atmosphere and heats the Earth’s surface.
• The Earth radiates longwave radiation back into space, but some is absorbed by CO2.
• This helps keep our planet warm
• However, volcanic activity continually adds CO2 to the atmosphere.
• If levels of CO2 were not being regulated in some manner, we would have entered a runaway greenhouse effect, and our planet would become too warm to sustain life.

Question 12

Regulation of CO2 in the atmosphere occurs via numerous pathways.

We will consider one here:

Answer 12

1. As CO2 levels increase in the atmosphere, the greenhouse effect will cause temperatures to rise.
2. Increased temperatures = greater evaporation of oceans and more cloud formation. CO2 dissolves in water in the atmosphere, forming carbonic acid H2CO3 (acid rain).
3. Acid rain falls on the land, causing silicate weatherings at the surface. This releases trace materials and nutrients into the oceans. In response, marine algae bloom and use the calcium and bicarbonate ions to produce their calcite shells, which, when they die, sink and become part of the sediment on the ocean floor.
4. Silicate weathering effectively “scrubs” CO2 out of the atmosphere by forming carbonic acid and weathering rocks. As a result, this process reduces the greenhouse effect and global temperature.

Question 13

Positive Feedback

Answer 13

a movement in the SAME direction as the stimulus.

Question 14

Earth example of positive feedback - thawing of permafrost in global warming context

Answer 14

1. Permafrost is ground that remains frozen throughout the year. As permafrost thaws, the organic matter frozen within it starts to decompose.
2. This decomposition is carried out by microorganisms and fungi, breaking the organic material into simpler compounds.
3. One of the byproducts of this decomposition process is methane.

Question 15

Earth example of positive feedback - thawing of permafrost in global warming context; METHANE - what is it?

Answer 15

• Methane is produced in anaerobic (oxygen-free) conditions by certain microorganisms called methanogenic archaea.
• These microbes thrive in the low-oxygen environment of waterlogged and oxygen-depleted soils, common in thawing permafrost.

Question 16

Earth example of positive feedback - thawing of permafrost in global warming context; METHANE - greenhouse effects?

Answer 16

• Methane is a potent greenhouse gas, with a much higher global warming potential than carbon dioxide over shorter timescales.
• When released into the atmosphere, methane traps heat, further warming the planet.
• This can lead to a feedback loop, where increased methane emissions from thawing permafrost contribute to further climate change, accelerating permafrost thawing and methane release.
• The stimulus (heating) causes the system to move in the same direction as the stimulus, more heating; an amplification!

Question 17

two main carbon cycles:

Answer 17

• The formation of fossil fuels (coal, oil, and gas) and the formation of carbonate rocks and sediments.
• The formation of fossil fuels and carbonate rocks is sometimes referred to as a biological pump, as life is effectively ‘pumping’ carbon dioxide out of the atmosphere and into the geosphere.

Question 18

1) Fossil Fuels

two main carbon cycles:

Answer 18

• Fossil fuels are naturally occurring hydrocarbon resources located within the Earth’s crust.
• Plants on land and algae in the oceans remove CO2 from the atmosphere during photosynthesis to form their tissues.
• If buried, they may be transformed into coal, oil or natural gas, locking away that CO2 in the geosphere.
• Eventually, those rocks and the fossil fuels they contain are exposed at the surface, weathered and return the CO2 to the atmosphere. When fossil fuels are extracted from the subsurface and burned, humans are prematurely releasing the CO2 and effectively short-circuiting the cycle.

Question 19

2) Carbonate Rocks - Carbonate rocks are composed of the mineral calcite, CaCO3

To form calcite, you need…

two main carbon cycles:

Answer 19

calcium (Ca2+) and bicarbonate ions (HCO3-).

Question 20

Where can we find calcium (Ca2+) and bicarbonate ions (HCO3-).

two main carbon cycles:

Answer 20

• Silicate weathering breaks down rocks, releasing calcium and bicarbonate ions, which are transported to the oceans by rivers.
• Aquatic organisms combine the bicarbonate and calcium ions dissolved in seawater to form their calcite(calcium carbonate) skeletons.
• Over time, these calcite skeletons accumulate in the deep ocean or on the flooded margins of continents in shallow water, forming carbonate sediments.
• Carbonate sediments on oceanic lithosphere can be carried down on a subducting plate where they melt, releasing CO2 that returns to the atmosphere via volcanic activity at volcanic arcs and divergent boundaries.
• Carbonates that accumulate on continental plates are converted by diagenetic (rock-forming) into limestones.
• These limestones may become involved in tectonic events, causing them to transform through heat and pressure into a metamorphic rock called marble with an associated release of CO2 that escapes into the atmosphere.
• The cycle is variable, but around 150 million years would be typical

Question 21

Venus Today

Answer 21

• Surrounded by clouds that hide its surface features: between 30 and 60km above the surface, clouds mainly comprise sulfuric acid droplets.
• The atmosphere is composed of 96% CO2 and generates a potent greenhouse effect, almost a million times stronger than Earth’s.
• Surface temperatures are hot enough to melt lead!
• Atmospheric pressure at the surface is 90 times that of Earth.
• Around 75% of the planet’s surface are lowland lava planes – probably the result of significant volcanic eruptions.

Question 22

Venus’ 2 continent-like mountainous areas

Answer 22

• Aphrodite (similar in size to Africa) around the equator and Ishtar (similar in size to Australia) in the northern hemisphere.
• Ishtar has the highest elevation - The Maxell Mountains, rising to about 11km.

Question 23

Venus - Volcanoes

Answer 23

• Many have been uncovered on its surface
• As there is little erosion, sediment deposition, or active tectonics on Venus, many older volcanoes have been preserved.
• Volcano types include broad “shield volcanoes” like those in Hawaii and unusual features called pancake domes that possibly formed as very viscous lava erupted under Venus’s high atmospheric pressure.

Question 24

There is indirect evidence of continuing volcanic activity on Venus - HOW?

Venus - Volcanoes

Answer 24

• Atmospheric SO2 levels vary over time, possibly indicating occasional input by volcanic events.
• In addition, the Venus Express probe detected a “hot spot” near Sapas Mons shield volcano between 2008-2009 that could be attributed to hot magma moving into an area before an eruption.

Question 25

Is Venus active today?

Answer 25

* Venus does not have active, Earth-like tectonics operating on it today. * Venus can be considered to consist of **one single "plate," often called a "stagnant lid."** * There is some **evidence of compression and stretching of the crust, possibly caused by the movement of materials in the mantle**, but there is **no active subduction or divergent boundary-type rifting.**

Question 26

Despite its current condition, it is possible that Venus demonstrated more equable conditions between... | + what? ## Footnote The Evolution of Venus

Answer 26

* 4.5 and 3.5 Ga. * The planet may have also had liquid oceans at this time * If this is the case, much of the CO2 currently in Venus' atmosphere could have existed dissolved in the oceans and locked away in rocks. * It has been suggested that if liquid oceans did exist on Venus, perhaps life also evolved, just as it did around the same time on Earth

Question 27

How did the runaway greenhouse effect occur?

Answer 27

* The sun's luminosity has increased over time. * As Venus was closer to the sun, and as solar luminosity increased, the Venusian oceans would start to evaporate into the atmosphere * Water vapour is a very powerful greenhouse gas. * On Venus, as temperatures continued to increase (in part due to the greenhouse warming effect of the water vapour), the Venusian oceans eventually boiled away. * As the water evaporated, it would also release the dissolved CO2 it contained, adding to the greenhouse effect. * As surface temperatures continued to increase, **CO2 started to bake out of the rocks**, adding to the CO2 in the atmosphere. The increasing volumes of greenhouse gases led to a situation referred to as a runaway greenhouse effect.

Question 28

What happened to the water in Venus' atmosphere?

Answer 28

* Venus does not have a magnetosphere, just a weak magnetic field. * As a consequence of this, ultraviolet radiation was able to strip the hydrogen from the water in the atmosphere, allowing it to escape to space. * The oxygen produced would have combined with rocks at the surface. This lack of water may explain why modern Venus has no plate tectonics. * HOW? Water introduced into the mantle on Earth may help reduce its viscosity and allow for subduction processes to occur.

Question 29

OVERALL - CO2 sits in the planet's atmosphere: HOW?

Answer 29

With no cycling of carbon facilitated by a biosphere or long-term tectonic processes

Question 30

Although Venus is relatively inactive today, there is evidence that a significant event occurred around __, suggested by what?

Answer 30

* 300 - 600 million years ago, suggested by the somewhat limited number (around 1000) of craters on its surface * The relatively young Venusian surface may be due to a "resurfacing event," perhaps caused by a time of accelerated volcanism that smothered older crust in new layers of lava * Another suggestion is somewhat more catastrophic; if Venus no longer had active plate tectonics, the heat flow from the interior would be reduced, meaning the mantle would become hotter. It is possible that the mantle became so hot that it melted much of the old crust

Question 31

What type of state is Venus in now?

Answer 31

* It is important to understand that **Venus is no longer considered to be in a runaway greenhouse state**. * It has reached a VERY hot equilibrium state, perhaps with the occasional addition of CO2 from volcanic activity.