i want to know who came first plants or humans because plants need co2 which is provided by us and we need o2 which is provided by plants it is same as who came first the egg or hen 

Dear student,
Please find below the answer:

If we look at the timeline of evolution, it was plants that appeared on earth before human beings. The earliest land plants showed up on earth around 470 million years ago while the first human forms appeared in Africa around two million years ago

Hope this clears your doubt.
Regards.