Why are humans on earth?

“Strange is our situation here upon earth. Each of us comes for a short visit, not knowing why, yet sometimes seeming to a divine purpose. From the standpoint of daily life, however, there is one thing we do know: That we are here for the sake of others...for the countless unknown souls with whose fate we are connected by a bond of sympathy. Many times a day, I realize how much my outer and inner life is built upon the labors of people, both living and dead, and how earnestly I must exert myself in order to give in return as much as I have received.”

- Einstein

If you are religious, refer to Littletad's answer. If not, we are here only by chance. We could just have easily ended up on another planet in a different galaxy, and our purpose would be to simply live.

Also, humans are animals.

According to the Bible and it's interpretations, were put on earth to know God. This requires us finding him, as he already knows us.

According to science, were the descendants of apes and monkeys and of course the Big Bang theory. And the list goes on from here.

A philosophical question needs a philosophical answer.

Man is not predefined: each act of any human being adds something to the definition of 'Man' and 'Human'. The definition will be complete when the last human being dies. In short but less clear: "existence precedes essence" (Existentialism is a Humanism, essay by Jean-Paul Sartre, well known French twentieth century philosopher)

(or: the phenomenon precedes the 'noema', to say it as Edmund Husserl would have put it)

Because of his ideas the works of J.-P. Sartre were put on the index of forbidden books by the Roman Catholic Church in 1938

Thus: no known purpose since there isn't yet a complete definition of what 'Human' means.

We are earths infection

Once upon a time Lucifer leaned on God's armchair, and said: "Hey, pops, you know, I just realized something. Because you created that expanding universe over there on the principle of constant energy, your own laws make a perpetual motion machine an impossibility."

"Yes, my child," replied God.

"But you're supposed to be all-powerful."

"Are you going somewhere with this?"

"Well, if you can do anything, then make a perpetual motion machine that is sustainable in that universe."

Cue life.

To make a difference. Whether that be to save someone from certain death, or to raise up an individual when they are feeling low. Every moment we breathe we have an opportunity to make a difference; however, it is mere "choice" if we would like to.

Best regards,
ArtistBBoy

Because we evolved over millions of years. We really have no great purpose.

if you're alive, and you are not an animal, then you're a plant...are you a plant?

it would seem you have no purpose lol.

to eat and reproduce, just like every other creature.

why is any animal on earth? there is no reason. we each create our own purpose.