Climate and the Carbon Cycle
Before the presence of fungi and land plants, Earth's atmosphere was very different than what it is now. It
contained high levels of carbon dioxide, which kept Earth's surface temperature higher than it is today.
The early appearance of fungi and land plants are linked to many changes, including changes to the
chemical composition of the atmosphere. These changes made life possible for a wide range of new
organisms.
These new organisms could perform functions that more primitive organisms could not. Plants used the
abundant carbon dioxide, combined with water, to create energy for cellular processes through
photosynthesis. Photosynthesis released oxygen into an atmosphere that typically contained only 5%
oxygen gas. Lichen, a type of fungi, lived symbiotically with photosynthesizing organisms, like algae. They
produced acids that dissolved the rocks upon which they lived, releasing calcium deposits. These
deposits, carried toward the ocean by rainfall, would bond with dissolved carbon dioxide and water
(carbonic acid) and eventually create calcium carbonate. This prevented carbon atoms from forming
carbon dioxide and therefore reduced the amount of carbon dioxide in the atmosphere of the prehistoric
period. Figure 1 illustrates this process.
Figure 1.
✔Question 6
Which TWO statements are correct about interactions described in the passage?
A
B
C
D
E
Lichen dissolving rocks is an interaction between the biosphere and the geosphere.
Fungi and algae living together is an interaction between the geosphere and
hydrosphere.
Carbon dioxide reacting with calcium is an interaction between the atmosphere and
biosphere.
Algae releasing oxygen for land organisms is an interaction between the hydrosphere
and geosphere.
Plants using carbon dioxide for photosynthesis is an interaction between the biosphere
and atmosphere.