I'm not sure what YOU already know about photosynthesis and cellular respiration.... however, you SHOULD know that the two are beautifully linked to one another!
Photosynthesis equation:
6CO2+6H2O -> C6H12O6+H2O
Cellular respiration
C6H12O6+H2O -> 6CO2+6H2O
Notice something? The substrates of one equation are the products of the other! We rely on plants for their photosynthetic reactions - and plants benefit from us (not really because there is already a TON of CO2 in the atmosphere) from our cellular respiration
***we like their oxygen and they like our carbon dioxide!
:) I hope that helps! Let me know if you need any more elaboration!
The earliest known life forms on Earth are putative fossilized microorganisms found in hydrothermal vent precipitates. The earliest time that life forms first appeared on Earth is unknown.