When Earth was young, its atmosphere had no free ____.
A) nitrogen
B) oxygen
C) helium
D) carbon dioxide
E) water vapor

Name: When Earth was young, its atmosphere had no free ____. A) nitrogen B) oxygen C) helium D) carbon dioxide E) water vapor
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Question

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When Earth was young, its atmosphere lacked free oxygen. Oxygen levels began to rise significantly with the development of photosynthetic organisms, which started producing oxygen as a byproduct of photosynthesis.

When Earth Was Young, Its Atmosphere Had No Free ____