Oxygen

Our life in this planet,

became possible due to oxygen,

promoting aerobic respiration, 

among various lifeforms,

for generating energy. (ATP) 

Primordial earth was difficult,

with limited free oxygen in air,

so, anaerobic were flourishing, 

until the rise of cyanobacteria,

causing great oxygenation event. 

There were mass extinctions, 

followed by period of fluctuations, 

where oxygen concentration rose,

leading to emergence of insects,

subsequently reptiles & mammals. 

Trees were massive, large hoards, 

due to high oxygen & carbon dioxide,

yet, concentration decline with time,

now, become ideal for human life,

as we inhale and utilize them. 

Oxygen... 

We need to preserve the balance,

for maintenance of the equilibrium, 

or hypoxia causes, loss of our organs,

while hyperoxia, oxidative damages,

impairing cellular functions.