Question

a scientist studying early earth conditions would expect to find early organisms
a) lived on land surfaces
b) required oxygen for survival
c) were large and complex
d) lived in ancient oceans

in photosynthesis, what is considered the \waste product\?
a) carbon dioxide
b) water
c) sugar
d) oxygen

the oxygen in earths atmosphere today exists because:
a) it was present since earths formation
b) it came from volcanic outgassing
c) ancient cyanobacteria released it as a waste product of photosynthesis
d) it was delivered by meteorites

Explanation:

1. Early Earth's surface was inhospitable for land - living organisms. Oceans provided a more stable environment for early life. Early organisms were simple and did not require oxygen as the early atmosphere had little oxygen.
2. In photosynthesis, plants use carbon dioxide and water to produce sugar and oxygen. Oxygen is the waste product released into the atmosphere.
3. Oxygen in Earth's atmosphere today is mainly due to the photosynthetic activity of ancient cyanobacteria which released oxygen as a waste product of photosynthesis. Earth's early atmosphere had very little free - oxygen. Volcanic outgassing and meteorites did not contribute significantly to the current oxygen levels.

Answer:

1. d) Lived in ancient oceans
2. d) Oxygen
3. c) Ancient cyanobacteria released it as a waste product of photosynthesis