riddle - What is it in my eyes that will result in humanity's demise?

The following stanzas
Are hints to the answer
Each a part of the end
Their piece they defend

I am found out in the ground
I can be bought by the pound
I'm put on the line

So in the end you can dine

I am a basic desire
That many require
I get you places
And contribute in races

Some find me childish
Some surpress me in kindness
But even if brief
After our encounter you'll feel a sense of relief

You have all you need
Now complete this one deed
What is it in my eyes
That will result in humanity's demise?