Chapter 29, Problem 9RQ

To determine

The key developments in life occurred during Precambrian time.

Answer to Problem 9RQ

The formation of stromatolites during the mid Precambrian–the Archean eon and the evolution of the single-celled organisms and primitive multicellular plants and animals during the end of Precambrian–the Proterozoic eon are the key developments in life occurred during Precambrian time.

Explanation of Solution

Precambrian time is the time of hidden life of the Earth, that is about 4.5 billion years ago. It was the time of Earth formation and lasted until about 543 million years ago.There are two significant developments that occurred life during the Precambrian Time.

The first one took place during the Precambrian -- the Archean eon, and it was the development of simple life structure called stromatolites. Stromatolites were the algae-like colonies of cyanobacteria that were interlayer with carbonate sediments. Stromatolites sustained with low oxygen environments of that time. Further, these organisms evolved a simple form of photosynthesis, that later helped in providing an oxygen-rich environment. This atmosphere was responsible for the evolution of the single-celled organisms and primitive multicellular plants and animals during the end of Precambrian–the Proterozoic eon.

Conclusion:

Therefore, the formation of stromatolites during the mid Precambrian–the Archean eon and the evolution of the single-celled organisms and primitive multicellular plants and animals during the end of Precambrian–the Proterozoic eon are the key developments in life occurred during Precambrian time.