Most of the earth's oxygen occurs in the form of minerals in the crust and mantle. the oxygen that is available in the atmosphere is used primarily by plants, animals, and bacteria to perform cellular respiration.

why is running out of oxygen still not a real concern?

micro/nanoscale topography surface exhibits many prominent properties and is extensively employed in biomedical device, microfluidic device and energy device fabrication. additionally, the clinical applications of biomaterials can be largely expanded with of nanostructured surfaces.