Module 2 Intro
1. Module 2 Intro
1.8. Page 2
Module 2—Biosphere Equilibrium and the Impact of Humans
Explore
Read
Read pages 55 and 56 of your textbook to learn about the geologic evidence for the change in atmospheric composition.
anoxic: lacking free oxygen
At one point, the atmosphere was anoxic. As organisms evolved and the number of producers increased, the composition of the atmosphere changed from high concentrations of carbon dioxide and low concentrations of oxygen to higher concentrations of oxygen and lower concentrations of carbon dioxide.
Self-Check
stromatolites: sedimentary rock in oceans built from fossilized
micro-organisms, such as bacteria
SC 1. How do scientists use the evidence of stromatolites as an indicator of changing atmospheric composition?
Self-Check Answer
SC 1.
Stromatolites aged 2.5 billion years contain black bands of iron oxides to indicate rising levels of oxygen in oceans. Stromatolites less than 1.8 billion years old do not have these black bands. Scientists think that this indicates that all of the iron in the ocean was bound to oxygen molecules. Since there was no more iron left for oxygen to bond with, oxygen was able to build up as a gas and eventually escape to the atmosphere.
Try This
TR 1. The Changing Atmosphere and Global Warming
The atmosphere is currently composed of 21% oxygen and 0.03% carbon dioxide. Photosynthesis, cellular respiration, and other processes such as fossil fuel combustion combine to create the composition of the atmosphere. What would happen if current levels of oxygen and carbon dioxide were to change?
You will be asked to explore this question in your Module 2: Lesson 2 Assignment. Your responses to TR 1. should be saved/written on this document.