Alife-form in the precambrian time was

Cynobacteria

Explanation:

The Precambrian time is the earliest period of earth history. It is preceded by the Cambrian time hence got the name. The earliest living organism in the Precambrian time was the Cynobacteria. It has been found in the fossil record of 3.4 billion years ago. They were the primitive organisms which were capable of conducting photosynthesis and producing oxygen. The abundance of Cynobacteria has resulted in the increase in abundance of oxygen into the atmosphere.  

weathering - colorado river carves land in arizona to form the grand canyon. cracks form in a sandstone wall surrounding a house. a marble statue near the science museum is changing color due to rainfall

erosion - after a rainstorm, soil and rock piees litter the roadways. the sand dunes in the sahara desert are changing shape.

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