Biological macromolecules are synthesized by dehydration 
synthesis reactions and are broken down by hydrolysis 
reactions.
<h3>What are Biological macromolecules?</h3>
These are formed from smaller compounds and are necessary 
for proper life functions of cells. Examples of these 
macromolecules include:
Dehydration synthesis involves the loss of water molecules in 
the process while hydrolysis reaction involves the addition of 
water molecules.
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Answer:
The fossils that provide information on the formation of an oxygen-rich atmosphere are the stromatilites from the Precambrian era. These are layered and columnar fossils consisting mainly of cyanobacteria which were the original life form back then. These bacteria took in carbon dioxide and produced oxygen by photosynthesis as early as 2.5 billion years ago (the earth is about 4.5 billion yrs old).
Explanation: