1) The environment of nebulas attract the dust and gas together and forms the necessary components of a star.
2) It is created by comparing different stars by their luminosity and color.
Answer:
3.5 billion years ago, or in the Eoarchean Era.
Explanation:
The first known single-celled organisms appeared on Earth about 3.5 billion years ago, roughly a billion years after Earth formed. More complex forms of life took longer to evolve, with the first multicellular animals not appearing until about 600 million years ago.
The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago, during the Eoarchean Era.
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