Early Earth and Theories on the Origins of Life! In your investigation today, you will explore the early experiments with life on earth and then create proto-cells in the laboratory!
Earth History Earth History: • Evolution is studied using concepts about earth history. The earth is between 4.3 and 4.5 billion years old. • Approximately 3.9 billion years ago, the surface was likely cool enough for water vapor to condense. (Oceans formed.) • Many of these events and organisms are recorded on the geologic time scale. • As geologists provided evidence about the age of the earth and the rate at which changes happened, biologists began to suspect that life, and life forms also changed over the same time. • Geologic and evolutionary change is a long and slow process. • People wondered, how did life arise? http://www.youtube.com/watch?v=QDqskltCixA
First Ideas: Spontaneous Generation • Aristotle about 2300 years ago argued that air provided a vital life force that could produce life from nonliving substances. This is called spontaneous generation. • The idea of spontaneous generation prevailed for thousands of years. • What do you think could have been the implication of this theory on ideas of human reproduction? • This idea was not formally tested until the 1700s.
Key Scientists – Origin of Life Remember, around 1678, Anton van Leeuwenhoek observed “animalcules” in water. We now know that these are protozoa. Francesco Redi (1626-1697) • First strike against spontaneous generation, his work: • Experimental Group: Covered jars with meat = NO maggots • Control Group: Meat in uncovered jars = maggots • Conclusion: Only flies where there are maggots AND only maggots where there had been flies… flies must come from flies. • It was concluded and believed they were a product of spontaneous generation from a “vital force” or life force in the air. • *As the microscope became a widely used tool for scientists, microorganisms were seen everywhere. What do you think people thought this “vital force” might be?
Key Scientists – Origin of Life Lazzaro Spallanzani (1729-1799) • Experimental Group: Boiled meat broth and sealed it in flasks = no microorganisms • Control Group: Boiled meat broth, unsealed flask=microorganisms. • Conclusion: Only had presence of microorganisms when they had access to the broth. • *His doubters claimed he had killed the “vital force” in the air when he boiled the broth and it could then not generate life. It was convincing enough to keep the belief of spontaneous generation going for another 100 years! Why do you think when presented with scientific evidence, that society still clung to the idea of spontaneous generation?
Key Scientists – Origin of Life Louis Pasteur (1822-1895) • Experiment: Boiled broth and enclosed it in an “S” curved neck flask. It was open and exposed to air, however not directly. Exposed for 1 year, no microorganisms; Removed “S” curve and exposed it for 1 day! = microorganisms • Conclusion: Spontaneous generation was disproved and biogenesis theory was substantiated. (Confirmed, make real or actuated) Contamination came from other microorganisms, not “air”. • Modern biologists support biogenesis, the idea that “living organisms only come from other living organisms.” • That then brings up the question of how life began on Planet Earth. • If Life can only come from life, we know at some point there had to be a start to “life”… • Where would you start looking for early life?
Alexander Oparin (1894-1980) NO EXPERIMENTS!! Earth’s early atmosphere: HCN, CO2, CO, N, H, S, HOH 1936 - Stated that the earliest living organisms on earth were simple heterotrophs (organisms that cannot make their own food) Knew these elements (in the form of various gases) were present in the earth’s early atmosphere. When heated (geologic activity) they might form organic compounds. Once condensed these compounds would be in earth’s water bodies. Oparin: “Life arose from the oceans.” He believed that energy from lightning and the sun can spark chemical reactions to create macromolecules like proteins. Key Scientists – Origin of Life Oparin’s Ideas: a. Heterotrophs ate the organic molecules in their environment until the food sources were very scarce b. Organisms needed another source of energy c. Autotrophs evolved (organisms that can make their own food source)d. Oxygen became prevalent in environmente. Cellular Respiration possible f. Eukaryotes evolved
Formation of Organic Compounds • Stanley Miller (1930- ) and • Harold Urey (1893-1981) • Miller & Urey’s experiment: • Mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on primitive earth. • C, H, N, O all known to exist on earth since the planet was formed. How did they turn into the fundamental organic compounds we know today? • Used Oparin’s concept and designed a contained experiment. • Lightning with atmospheric gases created amino acids and eventually life! • 1950’s, amino acids heated without oxygen, they formed AMINO ACIDS !! • Why is this significant? • Same with ATP and nucleic acids!
Key Scientists – Origin of Life Sidney Fox (1912- 1998) • -Studied the development of the first cells; found structures that have some cell life characteristics. • Microspheres – microscopic droplet enclosed by a membrane of organic molecules. (Predominantly proteins.) • They can form buds, split and take up certain substances from surroundings. • Sydney Fox produced protocells by heating solutions of amino acids. • Coacervates – small organic droplet formed by different types of organic molecules. • They can grow and take up substances from surroundings. (lipid bi-layer) • NOTE: These are NOT ALIVE no heredity, instead of reproduction, they form spontaneously under proper conditions. • Remember back to the Ecology unit, what are some of the criteria to be considered living? • What is something else you know of that is not considered to be alive? Microspheres Coacervates
Key Scientists – Origin of Life • Lynn Margulis (1938- ) • Conducted experiments in the 1960’s • Evidence: • 1. Mitochondria and Chloroplast DNA is similar to bacterial DNA. • 2. Mitochondria and Chloroplasts have ribosomes who size and structure resemble bacteria. • 3. Mitochondria and Chloroplasts reproduce by binary fission like bacteria. • She determined the endosymbiont theory that ancient prokaryotes became the first cellular organelles. • This is significant because this was one of the first driving forces of the theory of evolution!
The Evolution of Cells • 1st cells were prokaryotic heterotrophs. Chemosynthetic bacteria came next like archaebacteria. • Photosynthetic cells came later and added oxygen and the ozone to the atmosphere. • Allowed for eukaryotes because the new ozone layer protected from UV rays and oxygen allowed for aerobic respiration.
Origin of Eukaryotic Cells • Endosymbiont Theory: Eukaryotic cells arose from living communities formed by prokaryotic organisms. • The evolution towards eukaryotic cells began between 1.5 and 2 billion years ago in what is known as “endosymbiosis”: an internal, mutually beneficial relationship. • Small aerobic prokaryotes are thought to have entered and lived inside larger anaerobic prokaryotes. Later additional small photosynthetic prokaryotes are also thought to have entered and lived inside. • This is huge! Chloroplasts!! Mitochondria!! What is some evidence that you know of that would lead you to think that chloroplasts and mitochondria are unrelated to our genetic history?
Early Life on Earth: What we know now! Early Life on Earth: • It is known that at the beginning there was little to no oxygen available in the earth’s atmosphere. All living things must have been anaerobic. • The small size of the microfossils found indicates early organisms were prokaryotes. Likely these were heterotrophs (does not make their own food) that ate spontaneously formed organic compounds. • Supply and Demand: as the supply of these compounds became scarce, it became necessary to evolve. • Became Autotrophs (can make own food).
Early Life on Earth: What we know now! • The “archaebacteria” of today are likely similar organisms to those early life forms. • Archaebacterium – Kingdom of unicellular organisms that live in anaerobic marine sediments. • They learned to use chemosynthesis: CO2 is the carbon source for needed organic molecules, energy is obtained through chemical oxidation of inorganic molecules. • Oxygen, as it became present in the atmosphere was often harmful to early unicellular organisms, but by 3.5 billion years ago, some life forms had become photosynthetic and oxygen in the atmosphere increased. • Evidence of a group similar to the cyanobacteria of today; • Cyanobacteria – (blue green) a group of photosynthetic unicellular prokaryotes.