2 CHANGES IN THE GEOSPHERE, ATMOSPHERE AND BIOSPHERE

Question 1

The Great Oxygenic Event

Answer 1

Oxygenic photosynthesis led to the GOE 2.4-2.3 billion years ago

Question 2

Effect of photosynthesising cyanobacteria on the atmosphere

Answer 2

o Once the oxygen produced by cyanobacteria exceeded its precipitation in the ocean, it
accumulated in the atmosphere
o Oxygen molecules were struck by UV light, which split the diatomic molecule into two
separate oxygen atoms
o A single oxygen atom reacted with an oxygen molecule to fill up the electron orbit,
forming ozone and eventually the ozone layer (O+O₂O₃)

Question 3

BIFs Evidence

Answer 3

• The presence of BIFs provides evidence that the early Earth had an oxygen-poor atmosphere and the oceans were rich in dissolved iron.
• The deposition of iron oxide minerals in BIFs requires the presence of dissolved iron in the oceans, which was likely abundant in the early Earth’s oceans.

Question 4

Ozone Layer Formation

Answer 4

UV radiation from the sun splits oxygen molecules (O2) into 2 oxygen atoms.
The oxygen atoms then reacted with another oxygen molecule to create ozone (O3).

Question 5

What did cyanobacteria convert into? (Effect of photosynthesising cyanobacteria on the geosphere)

Answer 5

• Cyanobacteria converted water, sunlight and carbon dioxide into glucose and released oxygen as a waste product, via photosynthesis

Question 6

Why was there dissolved iron in early earth

Answer 6

Dissolved iron existed in early oceans as a result of terrestrial volcanoes, hydrothermal vents or the upwelling of iron-rich ocean currents

Question 7

What did oxygen produce with dissolved iron

Answer 7

• When oxygen was produced, it reacted with this dissolved iron to produce iron oxide, which settled to the ocean floor as a layer of insoluble iron oxide.

Question 8

How is chert layer formed in BIFS

Answer 8

Most early life forms had skeletons of silica, and oxygen was poisonous to them. When these organisms died, their bodies sunk to the ocean floor, forming a layer of chert on top of the iron oxide

Question 9

Bifs final formation

Answer 9

• Layers of silica and iron oxide continued to form on top of one another, creating banded iron formations.

Question 10

Effect of photosynthesising cyanobacteria on the atmosphere

Answer 10

• The early Earth was kept warm by methane, which is a greenhouse gas that traps heat. But once oxygen was produced, it reacted with methane in the presence of heat and light, to form carbon dioxide via combustion.

Question 11

What happened when carbon dioxide was produced in hydropshere

Answer 11

• Now that carbon dioxide was being produced, the Earth had a comparatively weaker source of warmth and cooled dramatically to form a glaciation event known as snowball Earth, which covered oceans with ice.

Question 12

What does decrease of carbon dioxide lead to in hydrosphere

Answer 12

• A decrease in dissolved carbon dioxide reduced acidification, making oceans more basic.