Transcript Slide 1
Microfossils Brandon McKee Overview What are microfossils? Where are microfossils found? How are stromatolites formed? What are the techniques used in determining a microfossil? Do microfossils occur elsewhere in our solar system? What are microfossils? Microfossils are just as their name implies, fossils that are microscopic. The oldest known and most familiar fossils, are from cyanobacteria in Archaean rocks. Fossil Evidence - for the origin and evolution of early life is limited. Data suggest that life is at least as old as the oldest rocks now known. Time Line eon era period when began myrs ago duration myrs Vendian 610 40 Sturtian 800 190 Karatau 1050 250 Yurmatin 1350 300 Burizan 1650 300 2200 400 2450 150 Randian 2800 350 Swazian 3500 700 Izuan 3800 300 Sinian (late Proterozoic) Proterozoic Riphean (middle Proterozoic) Animikean Huronian Precambrian Archaean 4000 Hadean Priscoan 4560 760 Other types of microfossils Aside from cyanobacteria, identifiable fossil bacteria are not particularly widespread. Under certain chemical conditions, bacterial cells can be replaced with minerals, notably pyrite or siderite (iron carbonate), forming replicas of the once-living cells, or pseudomorphs. Some bacteria secrete iron-coated sheaths that sometimes fossilize. Other bacteria may bore into shells or rocks and form microscopic canals within the shell; such bacteria are referred to as endolithic. A chain of cyanobacterial cells, Bitter Springs Chert of N. Australia 1 billion years old Where are microfossils found? Microfossils are found… Microfossils are thought to be found in stromatolites. Canada has three of the world's known examples at Red Lake, Ontario, Steep Rock Lake, Ontario, and near Yellowknife, Northwest Territories. Samples have been studied in Western Austalia and South Africa as well. How are stromatolites formed? Stromatolites - Mats of cyanobacteria or blue-green algae. Mats trap carbonate mud. Cyanobacteria grow up through the mud to form new mat layer. These structures trap sediment and sometimes secrete calcium carbonate. Stromatolites Today Best known site of stromatolite development to day is Solar Lake, which is located 90 feet away from the Red Sea on the Sinai Peninsula. Seepage from the Red Sea overlies saline water. The upper layer accumulates during winter rains and acts like a lens, focusing the sun’s energy into the deeper layer. The suns energy makes it so hot, higher forms of life cannot survive. Near the shore, stromatolites lie matted on the lake floor. In the middle of the lake, a thick mat floats some two feet below the water surface. This makes it possible to walk on water! How old are the fossils? Structures thought to be 3.4 - 3.5 billion years old by stromatolites of Western Australia. Filaments resembling cyanobacteria are found in the Warrawoona Group of Western Australia and 2.8-3.0 billion year old rocks of southern Africa. Testing Techniques There are different methods in testing whether or not an organism is biological. The two I want to talk about are: – The Fourier Analysis Technique and KPZ equation – Megnetosom Comparison Fourier Analysis Technique This is a method of recent study used to determine if stomatolites formed by biological organisms or by a lifeless, physical process. Through mathematical analysis, two Dr.’s (Grotzinger and Rothman) from MIT learned that stromatolites can sprout spontaneously on the seafloor. Rothman took 1.89 billion year old stromatolite and put it through the KPZ equation. This equation was developed to describe how particles settle out to form an undulating surface. An example of this is snow falling. When landing on a rocky terrain, there are basic characteristics of a KPZ surface. This equation predicts how particles behave as they form a surface— sometimes sticking where they fall, sometimes rolling downhill to stick somewhere else. Rothman transformed the hills and valleys on graph paper so there was longitude and latitude. Using the Fourier Analysis, he broke down the irregular meanderings of the layers into smaller undulations. Emerging was a broad spectrum of symmetrical little waves, that, when added back together, would reproduce the complex patterning in a stromatolite. The KPZ equation was then used to generate a similar spectrum of waves representing the hills and valleys of the stromatolite. Rothman was correct. The two spectrums were very similar. Similar enough to conclude that this ancient stromatolite could have been made by a physical process. The other type of testing technique is magnetosom comparison. Martian meteorites have been analyzed to determine biogenics. Magnetotactic bacteria produce well ordered membrane-bounded intracellular crystals of magnetite or greigite called magnetosomes. They are generally arranged in chains parallel to the long axis of the cell. The torque induced by the earths magnetic field on the bacteria causes them to align passively. Comparison of a meteorite from Mars and Earth could determine if there has been life on mars. There are six distinctive properties of magnetosomes. – Narrow size range and shape – Chemical purity – Few crystallographic defects – An unusual truncated hex-octahedral morphology – Elongation along the [111] axis – Alignment of chains within cells. The results of the comparison are as follows: – One fourth of the Martian magetites are truncated hexa-octahedral which are chemically and physically indistinguishable from terrestrial samples except for chain alignment. – They share 5 of the six characteristics that define the MV-1 biosignature – Alignment of the chains within the cells was not observed. – This is due to when organisms die, the membrane decomposes and the chain collapses. – Origin of the magnetites are possibly biogenic. Conclusion We have covered the following: – What are microfossils? – Where are they found? – How are stromatolites formed? – What are the techniques used to determine a microfossil? – Are there microfossils elsewhere in the solar system? References Earth, Vol. 6 Issue 2, 24, April, 1997 Proc. Natl. Acad. Sci. USA, Vol. 98, Issue 5, 2164-2169, February 27, 2001 Natrual History, Vol. 107 Issue 7, 88, September 1998 Rocks and Minerals, Vol. 75 Issue 5, 300, September/October 2000 Bioscience, Vol. 44 Issue 3, 181, March 1994 The Biology and Evolution of Fossil Plants. T.N. & E.L. Taylor. 1993. Hofmann, Grey, Hickman & Thorpe, 1999, Geological Society of America Bulletin 111:12561262)