How old is a rock if it contains 6.2% of its original 14carbon?
a. 780,000,000 years
b. 40,300,000 years
c. 21,480 years

you didn't give any answers to choose from so i can't with this but, i do know something that the mexican government would be worried about and that is the wall that donald trump is currently trying to get up.

crop rotation kepy different plants in the soil instead of once constintly. when switching out plants you have different nutrients being absorbed at different speeds and different roots growing differently therfore the spoil and water flow have to adapt and carry fresh nutrients to carry the constant changes that were going on in the soil.