Question

when did life start on earth and in water​

Answer 1

Scientists do not know how life began on Earth, but they do know that the early Earth's ... that the early Earth's atmosphere was composed of carbon dioxide, nitrogen and water vapor.

3.5 billion years ago
The age of the Earth is about 4.54 billion years; the earliest undisputed evidence of life on Earth dates from at least 3.5 billion years ago, and possibly as early as the Eoarchean Era (between 3.6 and 4.0 billion years ago), after geological crust started to solidify following the molten Hadean Eon.