One of the biggest questions in paleontology is how did life on Earth actually begin. It's a complicated one because we need the fossil evidence to construct the picture of how life might have actually started on our planet, and fossil evidence is scant. However, there are some very rare fossils which give us a glimpse into the beginnings of life on Earth. If you want to place a finger on the history of life on Earth, that point of this is where life begins, the Apex Chert is a pretty good place to start. Here some 3.5 billion years ago in what is Australia today tiny, little, single-celled beasties appear. And we find their fossils in these very rare, chert-like deposits, ideal for preserving this fine cell structure that might represent some of the earliest life on Earth. Some of the most beautiful examples of early life of Earth are the fossils of stromatolites. These are colonial organisms formed of blue-green algae. Now we call them blue-green algae, which is a bit naughty for the simple reason that is they're not algae. They are bacteria, but they're bacteria that use chloroplasts to photosynthesize to generate energy. So these are some of the biggest climate modelers that we can think of way back in time, for the simple reason they altered the environment completely. They generated oxygen to levels that would alter the whole face of our planet. And for this reason we should have a great interest in understanding the fossils of stromatolites. This is a beautiful cross section through a stromatolite colony, it's 1.5 billion years old, all the way from Mongolia. You can see these fantastic structures here, and there's layer upon layer, each of this was a living surface. And because the cyanobacteria that formed that surface mat, as they photosynthesize they also produce a gelatinous material outside of the cell. This picks up any sedimentary debris that's floating around, because these are living in marine environments. Now as that debris attaches to the little mound, it grows. For the simple reason that it accretes this material, layer by layer over year after year, as a function of this the mounds grow upwards. And we see this layer by layer, of each of these microbial mats forming a new surface each time it accretes the material from that environment in which it's living. The reason some these early forms of life could cling on to some of these extreme environments, was that they were adapted to do this. They had in their cell walls, compounds which allowed them to survive in such extreme environments, such as hopanoids. We do not have these same materials within our cell walls. We use cholesterol to support the cell wall membranes in our own bodies. This wouldn't allow us to live in the super heated ponds that we see in Yellowstone. Whereas creatures such as thermophilic bacteria can do so, and they continue to do that even today.
