During Earth's early history, microbial life on land contributed to the formation of soil. Soil formation, in turn, led to the evolution of land plants. Which term describes this chain of events?

The correct answer is - nitrogen fixation.

Explanation:

In soil formation microbes play an important role as they help in providing important compounds such as nitrogen by the process of nitrogen fixation that is used by the plants.

Nitrogen-fixing organisms mostly bacteria are free-living but some live in a symbiotic relationship with plants such as Azobacter or with other organisms such as Rhizobium.  

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