narrator: but sterols do more than tell us what kind of life was present. they provide evidence for its environment. this complicated maze of lines, circles, and arches is a road map of the metabolic pathways of living cells, molecular biologists' current knowledge of the sequence of reactions involved in creating compounds, like the sterols in pearson's rock sample. the chemical pathway for sterols is on the bottom of this chart down here, and the very first step in making a sterol consists of taking a precursor molecule and adding oxygen, or o2, to it. so, when we see these sterols in the ancient rock record, we can infer that they must have been formed by this pathway that requires oxygen. so in addition to being a good marker for the presence of eukaryotes, we, also, at the same time, have a tracer, or a record, that there should have been some amount of oxygen, or o2, present in the ocean system or in the atmosphere at that time. and so these are great classes of biomarker molecules because they can tell us something both about the biochemistry of the

narrator: but sterols do more than tell us what kind of life was present. they provide evidence for its environment. this complicated maze of lines circles, and arches is a road map of the metabolic pathways of living cells mocular biologists' current knowledge of the sequence of reactions involved in creating compounds like the sterols in pearson's rock sample. the chemical pathway for sterols is on the bottom of this chart down here, and the very first step in making a sterol consists of taking a precursor molecule and adding oxygen, or o2, to it. so, when we see these sterols in the ancient rock record we can infer that they must have been formed by this pathway that requires oxygen. so in addition to being a good marker for the presence of eukaryotes we, also, at the same time have a tracer, or a record that there should have been some amount of oxygen, or o2 present in the ocean system or in the atmosphere at that time. and so these are great classes of biomarker molecules because they can tell us something both about the biochemistry of the system, be

a way to read people's minds head to our website to find out how he's away in the invention plant sterols from your head. and how the habit is hurting business as of russia's ban on night time booze sales sales means foreign birds have to find new ways to ship all this and always just a click away on aussie dot com. you know sometimes you see a story and it seems so for lengthly you think you understand it and then you glimpse something else you hear or see some other part of it and realize everything you thought you knew you don't know i'm sorry welcome to the big picture. the. economic up and downs in the final. day the longer the deal and the rest of the life it's going be hazy it will be every week day. you know what you know. live from moscow welcome back nearly seven months of refusing to being force fed and alleged abuse with no end in sight that's been the daily experience for many gone tunnel day inmates in february the food protest has gone on for two hundred days now but president obama is still stalling on shutting down the facility that c. will the station is like right now a