Carbon Cycle 1

Question 1

When was the universe formed?

When did earth form?

When did sedimentary rocks form?

When did atmospheric O2 concentration start to rise?

When did old shelly fossils start to form?

Answer 1

Universe - formed 14 b.y. ago
Earth - formed 4.6 b.y. ago
Sedimentary rocks - 3.8 b.y. ago (require water to be formed)
Rise of atmospheric O2 concentration - 2.4 b.y. ago
Shelly fossils - formed 540 m.y. ago

Question 2

What was the origin of the elements?

What was the composition of elements in inter-space?

Answer 2

• after the Big Bang, hydrogen (H), helium (He) was formed
• a little bit of Boron, Lithium and Beryllium was formed
• formation of elements stop here as temp not high enough

Interspace

• 90% hydrogen
• 9% helium
• 1% other gases

Question 3

How are 1st generation stars formed?

Answer 3

1. clouds of hydrogen and dust form proto-stars, due to interactions between gravitational pull and thermal expansion
2. due to shortwaves/supernovas, clouds will start spinning and concentrate in a small space/volume, accumulating energy
3. hydrogen fusion happens after certain temp is reached
4. some mass is lost and released as light
5. formation of stars

Question 4

How are the bigger elements formed? (other than hydrogen and helium)

Answer 4

• a hydrogen runs out, no more hydrogen fusion, stars start to collapse, mass is very high
• gravitational energy > thermal expansion
• eventually, thermal energy gets high again due to high mass and helium expansion happens
• formation of Carbon, Nitrogen and Oxygen (usually stops at iron)
• stars with larger mass will trigger supernova when they collapse, can form even bigger elements (uranium)

Question 5

How was the solar system formed?

Answer 5

1. sun was formed by a collapsing interstellar cloud and gas
2. collapse caused spinning, and spread materials into a disk (solar nebula)
3. inner parts of the nebula are heated by the proto-sun. Consisting of iron and silicate materials, they condense to form planets (Mercury, Venus, Earth, Marcus)
4. the cooler outer parts of the nebula consisted of icy materials and formed giant planets (Jupiter, Saturn, Uranus, Neptune)

** sun is not a 1st generation star

Question 6

What is the asteroid belt?

Answer 6

• it is a failed planet

- Jupiter could have destroyed it with its gravitational pull

Question 7

What caused the formation of Earth’s atmosphere? (Why does it contain more than H and He)

Answer 7

1. Volcanoes
   - releases water vapour, carbon dioxide, sulfur dioxide, nitrogen, carbon monoxide and hydrogen sulfate
   - water vapour condenses to form oceans
2. Meteorite Impacts
   - frequent in the Late Heavy Bombardment (4 b.y.)
   - comets bring about gases, ice and dust to Earth
   - nitrogen and xenon isotopes match the Earth’s atmosphere
   - water isotopes, however, does not match the Earth’s atmosphere
3. Photosynthesis
   - photochemical dissociation by UV light developed oxygen-rich atmosphere (negligible amount today)
   - photosynthesis of bacteria and plants produce oxygen (around 2.4by)

Question 8

What were the evidence for the presence of oxygen after 2.4 by?

Answer 8

Evidence 1: Banded Iron Formation (BIF)

• iron is reduced in water as oxygen is absent. BIF deposits then occured when there was oxygen produced by cyanobacteria photosynthesis
• BIF formed before 1.9 by and 0.6-0.8 by

** ferrous iron - soluble, ferric iron - insoluble

Evidence 2: Iron Pyrite FeS2

• iron pyrite are only formed in reducing environments (lack oxygen)
• not stable in today’s conditions as it is easily oxidised to form Fe3+ and SO4-
• this was not formed after 2.4 by

Evidence 3:
- formation of stromatolite at around 2.4 by (Canada, Greenland, Australia)

Question 9

Why was atmospheric oxygen at 2.4 by much lower than present level until 540 my?

What was the evidence for oxygen increase at 540 my?

Answer 9

• rise of oxygen was delayed as oxygen was consumed by reduced gases (CH4, NH3) in the atmosphere, and dissolved iron in the ocean
• dramatic increase of multicellular life at 540 my with hard shells
• Cambrian period

Question 10

When did oxygen levels rise to higher than present level?

Answer 10

1. Carboniferous Period (~300my) - formation of giant dragonfly
2. Mesozoic Era (~100my) - dinosaurs

Giant sizes of creatures were a result of higher oxygen level

Question 11

Who were the famous scientists in studying deep-time climate?

Answer 11

1. Carl Sagan - Faint Young Sun Paradox
2. James Lovelock - Gaia Hypothesis (biosphere has a regulatory effect on Earth’s life)
3. Donald Canfield - biogeochemical cycles and ancient oceans