 Now that we know a little bit more about glycolysis, we can understand how working across field and disciplines in sciences can help us to solve some of the puzzles of science and advance each of those different fields. One of those puzzles is how the biology of cells fits in with evolution. Taking a look at glycolysis, scientists have found that it is one of the most widespread metabolic pathways across all life forms. Pretty much everything does it. It also occurs in the cytosol, which means it doesn't require any membrane-bound organelles. This has led scientists who look at cells to think that perhaps glycolysis existed very early on. If we head over to geology for a moment, we can look at the geologic time scale. When we talk about geologic time, we're talking about really long periods of time, and we'll start back over here at about 4,600 million years ago, or 4.6 billion years ago. So around about that time, the Earth was formed and solidified. Geologists have found that oxygen, the presence of atmospheric oxygen, only came to being on Earth around 2,700 million years ago. Scientists have found evidence for prokaryotes throughout history, the earliest of which have been found around 3,500 million years ago. Geologists have found the earliest evidence of eukaryotes around about 2,200 million years ago. So already this paints quite a picture. Scientists were around for almost 1,000 million years before anything was doing photosynthesis and putting oxygen into the atmosphere. How did they get their energy? Perhaps you remember the theory of endocytosis from earlier in the course, where the idea is that one prokaryote ate another one, and that was the start of membrane-bound organelles, which led to eukaryotes, but they all must have started as being prokaryotes. To fill in that time scale, first evidence of land plants occurs around 500 million years ago. Evidence of big dinosaurs about 200 million years ago, and we're pretty self-centred. Humans about 0.2 million years ago, or 200,000 years ago. So the combination of the evidence in the rocks, as well as our understanding of what happens in the cells, and those cell pathways, such as glycolysis, gives us more evidence towards the theory of evolution. If pretty much everyone does glycolysis in their cells, it would make sense that we all come from the same early ancestors.