how the bacterial colonization of those distant shores began is a puzzle that scientist david flannery is keen to solve, and a simple living algal mat offers a remarkable clue. it's much easier to interpret things in the fossil record if you have a modern example. here's a piece of rock from western australia in the pilbara that's 2.7 billion years old, and it has a very similar structure and it comes from a very similar environment. you can see the modern example is made up of these tuf and ridges and this polygonal pattern, and the fossil example is made up of the exact same stuff. smith: they may come in a range of shapes and sizes, but these high-rise bacterial communities have barely changed in billions of years. to swim here is to take a dip deep into the past. this is a time tourist's trip to a three-billion-year-old beach. we know that stromatolites dominated the ancient australian shorelines because you can still visit them, preserved in the rocks of western australia's pilbara region. the town of marble bar, population about 350 plus a few dogs, claims the dubious distinction