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The Cells That Changed the World (Adapted from the 2003 Windows to the Sea Expedition)

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The Cells That Changed the World (Adapted from the 2003 Windows to the Sea Expedition) Thunder Bay Sinkholes 2008 The Cells That Changed the World (adapted from the 2003 Windows to the Sea Expedition) FOCUS SEATIN G ARRAN G E M ENT Cyanobacteria Classroom style or groups of three to four students GRADE LEVE L MAXI M U M NU M BER O F STUDENTS 9-12 (LIfe Science) 30 FOCUS QUESTION KEY WORDS What are cyanobacteria, and how have they Cold seeps been important to life on Earth? Cyanobacteria Photosynthesis LEARNIN G OBJECTIVES Chemosynthesis Students will compare and contrast cyanobacteria with eukaryotic algae. BAC kg ROUND IN F OR M ATION In June, 2001, the Ocean Explorer Thunder Bay Students will discuss differences in photosynthesis ECHO Expedition was searching for shipwrecks by cyanobacteria and green algae. in the deep waters of the Thunder Bay National Marine Sanctuary and Underwater Preserve in Students will discuss the role of cyanobacteria in Lake Huron. But the explorers discovered more the development of life on Earth. than shipwrecks: dozens of underwater sinkholes in the limestone bedrock, some of which were MATERIA L S several hundred meters across and 20 meters Copies of “Cyanobacteria Discovery deep. The following year, an expedition to sur- Worksheet,” one copy for each student or stu- vey the sinkholes found that some of them were dent group releasing fluids that produced a visible cloudy (Optional) Cultures of live cyanobacteria and layer above the lake bottom, and the lake floor materials for microscopic examination near some of the sinkholes was covered by con- spicuous green, purple, white, and brown mats. AUDIOVISUA L MATERIA L S None Preliminary studies of the mats have found that where water is shallow (≤ 1.0 m) the mats are TEACHIN G TI M E composed of green algae. In deeper (about 18 One-half 45-minute class period for introduc- m) waters, mats are formed by filamentous purple tion, one to two hours for research outside of cyanobacteria. Mats near the deepest (93 m) class, and one 45-minute class period for student sinkholes are white or brown, but their composi- reports and discussion tion is presently unknown. The appearance of 1 Thunder Bay Sinkholes 2008 - Grades 9-12 (Life Science) Focus: Cyanobacteria oceanexplorer.noaa.gov mats near the deepest sinkholes is very similar to nized in this region: one near the land or lake mats observed in the vicinity of cold seeps and floor surface (the surficial aquifer) and the others hydrothermal vents in the deep ocean, which are in deeper bedrock named for the geologic time often formed by chemosynthetic bacteria. These periods when they were formed (the Cambrian- bacteria are able to obtain energy from inorganic Ordovician, Silurian-Devonian, Mississippian, and chemicals, and are a food source for a variety Pennsylvanian aquifers). The bedrock that forms of other organisms that inhabit cold seep and the Silurian-Devonian aquifer is primarily lime- vent communities. Biological communities whose stone and mineral formations from evaporating primary energy source comes from chemosyn- seawater. Both fresh and saline water are found thesis are distinctly different from more familiar in the Silurian-Devonian aquifer. biological communities in shallow water and on land where photosynthetic organisms convert the Sinkholes are common features where limestone energy of sunlight to food that can be used by is abundant, because limestone rocks are soluble other species. Hydrothermal vent and cold seep in acid. Atmospheric carbon dioxide often dis- communities are home to many species of organ- solves in rainwater to form a weak acid (carbonic isms that have not been found anywhere else on acid). Rainwater flowing over land surfaces may Earth, and the existence of chemosynthetic com- also pick up organic acids produced by decay- munities in the deep ocean is one of the major ing leaves and other once-living material. The scientific discoveries of the last 100 years. resulting weak acid can slowly dissolve limestone rocks to form caves, springs, and sinkholes. Scientists hypothesize that the source of the Sinkholes on land are known recharge areas for fluids venting from the Lake Huron sinkholes is the Silurian-Devonian aquifer (areas where water the Silurian-Devonian aquifer beneath the lake’s flows into the aquifer). But very little is known sediments. Aquifers are rocks and sediments that about the chemistry, geology, and biology of contain large amounts of water. Between 350 submerged sinkholes that may serve as vents for and 430 million years ago, during the Paleozoic groundwater in the aquifer. Water samples col- era, shallow seas covered what is now the border lected near these sinkholes is very different from between Canada and the United States between the surrounding lake, with much higher concen- Minnesota and New York. Over thousands of trations of sulfate, phosphorus, and particulate years, sand, minerals, and sediments accumu- organic matter, as well as ten times more bacteria lated on the seafloor, and were gradually com- compared to nearby lake water. These observa- pressed to form sandstone, limestone and shale. tions suggest that submerged sinkholes may be About 1.8 million years ago, the Great Ice Age biogeochemical “hot spots” inhabited by unusual of the Pleistocene epoch began and continued and possibly unknown life forms. At the same until about 10,000 years ago. During this time, time, water flow through submerged sinkholes four major periods of glaciation occurred, sepa- depends upon recharge from land. This means that rated by three interglacial periods. As the final sinkhole ecosystems are likely to be very sensitive glacial period came to a close, retreating glaciers to changes in rainfall patterns that may accom- along the U.S.-Canadian border revealed five pany climate change, as well as human alterations huge lakes that we now know as the Laurentian of these landscapes surrounding recharge areas. Great Lakes. In the Great Lakes region, aquifers These factors make understanding sensitive sink- are found in deposits of sand and gravel left by hole ecosystems an urgent necessity. glaciers, as well as in porous bedrocks (limestone and sandstone) that were formed much earlier Preliminary studies show that the composition in geologic time. Five major aquifers are recog- of the colored mats changes with water depth. 2 Thunder Bay Sinkholes 2008 - Grades 9-12 (Life Science) Focus: Cyanobacteria Mats in shallow (≤ 1.0 m) water are composed guide for inquiry. of green algae. Mats near the deepest (93 m) sinkholes, where there is little or no light, may be 3. Provide each student or student group with composed of bacteria, but their exact composition a copy of the “Cyanobacteria Discovery is presently unknown. Sinkholes in intermediate Worksheet,” and assign one of the following (about 18 m) depths are surrounded by mats species of cyanobacteria: formed by filamentous purple cyanobacteria. This Anabaena group of microbes includes some of Earth’s oldest Hapalosiphon living species, and are believed to be the “archi- Lyngbya tects” of the modern Earth atmosphere as well as Microcystis the ancestors of chloroplasts and mitochondria Nodularia found in the cells of eukaryotic organisms. Nostoc Phormidium In this lesson, students will explore some aspects Spirulina of Cyanobacteria biology. Alternatively, you may want to obtain live cul- LEARNIN G PROCEDURE tures of these or other cyanobacteria species 1. To prepare for this lesson: from biological supply companies and have stu- Review introductory essays for the Thunder Bay dents make drawings from microscopic exami- Sinkholes 2008 Expedition at http://oceanexplorer. nation. noaa.gov/explorations/08thunderbay/welcome.html 4. Lead a discussion of students’ answers to ques- 2. Briefly introduce the Thunder Bay Sinkholes tions on the worksheet. The following points Expedition, highlighting the discovery of flu- should be included. ids emerging from sinkholes on the lake floor, • Although they are often called “blue-green and the variety of mats found in the vicinity of algae,” cyanobacteria are not algae; they these sinkholes. Be sure students understand are bacteria. But they are the only bacteria the concept of an aquifer, and that the mats capable of photosynthesis and in this respect are likely to be living organisms (algae and/or are similar to algae and higher plants. bacteria) that can serve as food for many other organisms. Ask for possible reasons why mats • Cyanobacteria are found throughout the at different depths contain different organisms. world in varied habitats, including tree bark, Variations in the type of fluids venting from rocks, soil, fresh and salt waters, and in sym- sinkholes is one possibility. Another is declin- biotic relationships with fungi to form lichens. ing sunlight penetration with increasing depth. Tell students that the shallowest sinkholes, with • Stromatolites are fossilized mounds of abundant light, are surrounded by mats con- cyanobacteria. Although cyanobacteria taining green algae. The deepest sinkholes, are unicellular, many species grow in colo- with almost no light, have mats that probably nies or filaments that may be quite large. contain bacteria (though that isn’t certain as Stromatolites were widespread on Earth dur- yet). Mats near sinkholes at depth of approxi- ing the Proterozoic Era, and are the first reefs mately 18 m contain “blue-green algae.” Tell found in the fossil record. students that their assignment is to find out more about “blue-green algae,” using questions on • Stromatolites are the oldest known fossils, the “Cyanobacteria Discovery Worksheet” as a more than 3.5 billion years old. 3 Thunder Bay Sinkholes 2008 - Grades 9-12 (Life Science) Focus: Cyanobacteria oceanexplorer.noaa.gov • During the Archaean Eras before cyanobac- • Microcystins, Cylindrospermopsins, and teria were abundant, Earth’s atmosphere Nodularin are toxins produced by cyanobac- contained very little oxygen and was not suit- teria that may poison humans and other able for life as we know it today. The modern animals. Cyanobacteria that produce toxins oxygen atmosphere was generated by large are generally freshwater or brackish water populations of cyanobacteria during the species that form outbreaks called ‘”blooms,” Archaean and Proterozoic Eras.
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