why do we exist?

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i am from india, and am trying to find out the reason fr our existence on this earth. why do we exist basically? is there any purpose to our existence? why were we created? who created us? do we exist by default? or is there a more rational explanation? are there many planets like our earth in this universe? it doesnt make sense for someone to have such a vast universe just for a tiny planet like us with 5 billion humans. is there anyone who can provide some logical or rational arguments or answers to whatever i have written above? i am eager for responses. thanks.