The most common and most likely answer to this crossword clue is the 13 letter word FERTILISATION
I've seen this crossword clue in The Guardian
F
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Buddy explains!
The straight part
We know that "I start life that’s formed with tiny particle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i start life that’s formed with tiny particle = fertilisation.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FERTILISATION mean?
FERTILISATION noun- The act or process of rendering fertile.
- The act of fecundating or impregnating animal or vegetable gametes; especially, the process by which in flowers the pollen renders the ovule fertile, or an analogous process in flowerless plants
- The act of applying fertilizer to soil.