LESSON 3 MICROBIAL MATS Instructor’s Key AND ALIENS! Thermal Biology Institute Thermal Biology Institute Thermal Biology Institute Thermal Biology Institute BACKGROUND IMAGE: These strange- looking structures in Glacier National Park were created by the fossilization of ancient microbial mats called stromatolites. INSET: A cross section of a fossilized stromatolite specimen. 2 | MONTANA STATE UNIVERSITY THERMAL BIOLOGY INSTITUTE Aliens Among Us? We imagine alien life as looking much Though we have not yet discovered living organisms on another planet, the types of life that could different than what we encounter every survive on other planets would have to survive in day on Earth. Why is that? If you are conditions that are considered extreme on Earth. looking for life on Mars or another planet Scientists think that if we find life elsewhere in the Universe it is more likely to be an extremophile (a you’re almost certainly not going to find microbe that lives in an “extreme” environment) a tree or a bear. That’s because our planet than a little green man. now has an oxygen-rich atmosphere, lots Fossilized microbes of sunshine, liquid water and moderate Have you ever been to Glacier National Park? temperatures, but most other planets do Imagine walking on a high mountain trail and seeing a strange pattern of circles on the ground. (See not. Our planet is home to birds, reptiles, background photo.) Would you have any idea what flowers, grass and many other types of life you are looking at? They are actually a type of fossil that could not exist on any other planet that NASA is searching for on other planets! The circles are ancient fossilized microbial mats in our solar system because the resources that lived in this area when it was a shallow ancient they need to survive are not available on sea more than 1.3 billion (1,350 million) years ago. Millions of years of Earth’s changing climate and those planets. shifting tectonic plates have moved what was once a warm shallow sea floor to the top of a modern-day cold mountain. Old timers of the Earth These circular structures are fossils of a stromatolite. A stromatolite is a structure created by a microbial mat in which a rock-like layer of either sand or precipitated minerals has been trapped. The microbial mat consists of microorganisms such as bacteria and algae. Stromatolites are formed by microbial communities that consist of many species with different metabolisms competing for or sharing resources. (See the fossilized cross section of an ancient Glacier National Park specimen at left.) Stromatolites provide one of the most ancient records of life on Earth. Scientists have found fossil remains of stromatolites which date from more than 3.5 billion years ago. If stromatolites are a record of early life on our planet, they might be a record of life on another planet too. Imagine if life formed on Mars millions of years ago when Mars had shallow seas. Stromatolites used to be much more common on Earth than they are today and they are often found in the ancient fossil record. They were the dominant form of life on Earth for more than two billion years and are thought to be largely responsible for making our atmosphere oxygen-rich (Earth’s early atmosphere had little or no oxygen). Currently, stromatolites occur in only a few places, such as Shark Bay, Australia or in some of the hot LESSON 3 | MICROBIAL MATS AND ALIENS | 3 LIVING STROMATOLITES IN SHARK BAY, AUSTRALIA. Organisms in stromatolite formations are divided up by what they can eat and what conditions they can tolerate. springs of Yellowstone, because they require a typically called a food chain or more accurately, a location where they can form for years undisturbed food web. by humans and grazing or burrowing animals. How did early life forms get energy? Life by the layer The first forms of life on our planet must have Microbial mats are tiny ecosystems that have been autotrophs. Were they photoautotrophs layers much like a forest. Organisms living at harvesting sunlight, or chemoautotrophs relying the top of the mat use sunlight for energy and on chemicals? Scientists are divided on this perform photosynthesis like a forest canopy. issue, though more seem to be favoring the Organisms lower in the mat use chemicals chemoautotrophs hypothesis, mainly because produced by the microbes in the upper layer to that type of metabolism doesn’t require oxygen, get energy. They also recycle nutrients and help and we know that free oxygen was very scarce in with functions such as decomposition, just like the early stages of life on our planet. some of the organisms in a forest’s understory. Different strokes for different trophs Each layer of a microbial mat is dominated by microorganisms that thrive in the conditions autotrophs – produce food from inorganic of that layer and outperform other kinds of (non-living) things such as minerals life. Organisms compete and cooperate and (autos=self, troph=nutrition) are divided up by what they can eat and what photoautotrophs – use sunlight to conditions they can tolerate. create food/energy (photosynthesis) A web of energy chemoautotrophs – use chemicals to create food/energy (chemosynthesis) All living things need a way to get food, which gives them energy. Plants can create their own heterotrophs – eat other organisms or organic energy using sunlight, but we humans can’t, so carbon to obtain energy (heteros=different, we have to eat plants, or eat animals that eat troph=nutrition) plants. We are heterotrophs (heteros=different, troph=nutrition) because we must eat other organisms to obtain energy and organic carbon. All animals are heterotrophs, along with some CHEMO VS PHOTO Being a single-celled creatures. photoautotroph (using photosynthesis) Any organism that can harvest energy is a much more productive and directly from the nonliving environment and efficient way to get energy than being a chemoautotroph. It is estimated fix CO2 into biomass is called an autotroph, a word that means “self feeding” (autos=self, that the appearance of oxygenic photosynthesis increased biological troph=nutrition). productivity by a factor of between We can think of energy as “flowing” through 100 and 1,000! lifeforms, starting with the autotrophs (also called producers) and then moving to the heterotrophs (also called consumers), and then maybe to other consumers, and so on. This is 4 | MONTANA STATE UNIVERSITY THERMAL BIOLOGY INSTITUTE Like other solar-powered ALERT: RESERVE POWER photosynthesizers, AT CRITICAL LEVEL. cyanobacteria produces INSUFFICIENT SOLAR dissolved oxygen as a RADIATION FOR SUCCESSFUL YOUR byproduct of photosynthesis. RECHARGE… WARNING. Here we see how Earth’s The mat community contains MISSION atmospheric oxygen filamentous cyanobacteria originated bubble by bubble. that move between the DEPTH: 2.6MM AND sulfur-rich deeper layers and DESCENDING; the oxygen producing upper OXYGEN: NEGLIGIBLE; layers in a daily cycle. If the HYDROGEN SULFIDE: 75 crew can remember this, earliest forms of life on MICROMOLARS; they might have a chance to Earth. Microbial mats have PH 7.2 hitch a free ride back to the been around for over 3 surface. billion years making them When the sun goes down, Earth’s earliest biological the chemical output of the Watch the stromatolite communities. Finding the mat community adjusts for video and use the remains of microbial mats life in the dark. A peek at transcript of it below to on other planets would be the updated transponder answer the questions on powerful evidence that life data reveals a new set of your worksheet. Soon once thrived there. That’s readings. you will be analyzing why understanding microbial Because the only light your own microbial mats is of such interest to that gets down into the mat sample and you’ll NASA. deeper part of a mat is in the form of red to near need the information infrared radiation, the contained in the section bacteria here, purple sulfur you just read as well as bacteria, use that radiation facts from the video you and the hydrogen sulfate are about to watch. present to perform a kind of photosynthesis that doesn’t A microbial mat is a produce oxygen: anoxygenic Stromatolite community that changes photosynthesis. Video Transcript In the uppermost region dramatically in the first few of the mat, diatoms reign DEPTH 4.3 MM; millimeters. Descending, supreme. These single cells HYDROGEN SULFIDE: 125 the mat changes from a are encased in houses made MICROMOLARS photosynthetic oxygen of glass. Diatoms convert OXYGEN: 0 producing layer to a murky sunlight and carbon dioxide realm where sulfur munching into fuel molecules and bacteria prevail. oxygen through the process The activities of these of photosynthesis. simple life forms create an Imagine an exploration Now the explorer and alkaline environment where mission through a strange crew enter the realm of minerals accumulate and and hostile environment. filamentous cyanobacteria. over time a stromatolite Now place yourself inside Each strand is a chain of will form — one of the The mat, though relatively the imaginary vehicle, the single celled prokaryotes. No telltale signs to look for in thin, shows a steep .1 mm long Stromatolite nucleus in these cells, just a our search for life on other chemistry gradient from top Explorer. The mission long strand of DNA. worlds. to bottom. The explorer has is to probe a microbial DEPTH: .5 MM; descended through layers Someday, not so far away mat; a complex and very OXYGEN: 600 MICROMOLARS; that contain diatoms, then when an exploration ancient assemblage of HYDROGEN SULFIDE: cyanobacteria, purple sulfur vehicle from Earth begins microorganisms less than NEGLIGIBLE bacteria, and finally sulfate probing the soil on a planet 5 mm thick.