The Earth formed around 4.5 billion years ago. Over the past billions of years, evolution has greatly changed life as we see it today. If we transport ourselves back in time and look at cells, we will notice that they are extremely simple. But, in the present day, we notice that cells have become much more complicated beings with very complex processes that require many entities in order to function. The process of how this occurred is known as the endosymbiotic theory. This podcast will discuss what the endosymbiotic theory is and the evidence that supports it.