Because many living organisms begin in the womb similarly, showing that organisms have a common ancestor
They carry oxygen to your entire body, and carry carbon dioxide away from your body to be exhaled.
According to a source the answer is <span><u>Cyanobacteria were the first organisms to produce oxygen in water, which then escaped into the atmosphere.</u>
These cyanobacteria species were the first ones to "produce" oxygen as a by-product of the photosynthetic mechanisms which enables organisms to make their own food. </span>
I'm assuming you meant and frailness not fertility, in which case it is the oldest old period
A verified animal source such as animal planet or any website that doesn't have ads and has accurate info
