Plants

If only the majority of human beings would understand, that plants are indispensable for our existence!

If so: do you believe, men could still kill the forests as he has been doing this since decades? May be. Because...  

Deforestation, loss of soil and water pollution led to a significant decline of vegetation areas on our planet. But we need it! Plants are the primary producers of all essential and complex molecules we need for our metabolism. 

They absorb CO2 and have been accumulating the atmosphere with O2 since billions of years, too.

Now, the CO2 concentration ascends, while the O2 concentration slowly decreases...