Transcript:

In the early history of the earth, there wasn't any oxygen in the atmosphere. So, what happened about 4 billion years ago is that a tiny cyanobacteria figured out that if it ingests a water molecule and extracts the proton, it can liberate oxygen. And this is what happened. So, that oxygen liberation by the cyanobacteria led to an oxygen-rich atmosphere, which facilitated life as we know it. It's pretty interesting. 

And then, these bacteria learned to metabolize oxygen to make energy and these bacteria, eventually, were engulfed by a bigger bacterium to make what is today known as the nucleus of the cell. And it's pretty interesting because this nucleus of the cell is the mitochondria, which has its own DNA. It's a completely different DNA structure compared to the host species. So, it's an organism living inside of us that has the magic of metabolizing oxygen to make energy, without which life would not happen.