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Natural Selection and Evolution

Natural Selection and Evolution. Spring 2007 Dobson High School Hope Finzer. Earth’s History. Earth Origins:

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Natural Selection and Evolution

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  1. Natural Selection and Evolution Spring 2007 Dobson High School Hope Finzer

  2. Earth’s History • Earth Origins: 4.6 billion years old – originally a ball of hot molten rock – bombarded by meteorites and extreme volcanic activity – the atmosphere was inhospitable but volcanic gases paved the way for our current atmosphere

  3. Earth’s History • Earth’s Oceans: Formed about 3.9 billion years ago after the Earth began to cool and allow the water vapor to condense into water forming the oceans – its is in these oceans that the first living organisms appeared 3.5 billion years ago

  4. History in the Rocks • Fossils: Any evidence of an organism that lived long ago – classified by how the fossil is formed • Types of fossils: • Casts- A mold of an organism filled by minerals in the surrounding rock – produces a replica • Trace Fossils- Markings or evidence of animal activities – footprints, trails, and burrows

  5. History in the Rocks • Types of fossils: • Imprints- Fossils that form before sediment hardens into rock – leaves or feathers that fall into mud and leave imprints • Molds- When an organism is buried, it decays leaving an empty space that has the exact shape of the organism

  6. History in the Rocks • Petrified Fossils- • The hard parts of an organism are sometimes penetrated and replaced by minerals atom for atom, when minerals harden an exact stone copy of the original organism is produced • Amber-Preserved & Frozen Fossils • Entire, intact organism is caught in ice or tree sap (amber) – very rare – preserves the internal parts of organisms important to scientific study of extinct species

  7. What is Paleontology? • Paleontology- study of geological periods and fossil remains

  8. Why are sedimentary rocks important for Earth’s history? • Sedimentary rocks contain important information about the history of the Earth. • They contain fossils, the preserved remains of ancient plants and animals. • Differences between successive layers indicate changes to the environment which have occurred over time. • Sedimentary rocks can contain fossils because, unlike most igneous and metamorphic rocks, they form at temperatures and pressures that do not destroy fossil remnants.

  9. Sedimentary Rock formation

  10. Formation of Fossils in Sedimentary Rock a. organism dies and falls into a sandy or muddy bottom of a body of water or is carried there by floods b. overtime sediment is deposited on top of the dead organism until it is completely covered c. mud and sand begin to compress around the organism – forming a sequence of sedimentary rocks – usually only the hardest parts of the organism remain

  11. Formation of Fossils in Sedimentary Rock d. fossil becomes imbedded in the rock, then geological events, such as Earth movements or erosion, the fossil can come to the surface e. scientists discover the fossil and extract it from the surrounding rock – then the fossil is studied

  12. How do you tell the age of a fossil? • Relative Dating- the layers of sedimentary rock are layered with its newest layer on top and the oldest on the bottom – fossils are determined the same way - deeper fossils are older then shallower fossils

  13. How do you tell the age of a fossil? • Radiometric Dating- radioactive isotopes are used – the fossil emits a decay rate and scientists using radioactive isotopes whose decay rate is known and if the known decay rate matches the fossil the age can be determined – radioactive decay

  14. Earth’s Geologic Time Table

  15. Earth’s Geologic Time Table • Precambrian Era- • Life begins – 3.5 billion years ago – spherical and filamentous organisms that resemble photosynthetic bacteria cyanobacteria and dome-shaped stromatolites – Precambrian accounts for 87% of Earth’s history – prokaryotes dominated the early Precambrian era • Eukaryotes appeared about 1.5 billion years ago • By the time the Precambrian era ended about 544 million years ago the oceans were filled with unicellular and multi-cellular organisms such as algae, sponges, and jellyfish

  16. Earth’s Geologic Time Table • Paleozoic Era- • From 544 t 245 million years ago – characterized by the appearance of many plants and animals – • Scientists call this era the explosion of life- • Seas were filled with worms, echinoderms, and primitive arthropods (Examples: insects, spiders, lobsters, and crabs) • 1st half – fishes and earliest vertebrates appeared, some evidence of plant life on land • Middle – amphibians appeared • 2nd half – reptiles appeared

  17. Earth’s Geologic Time Table • Mesozoic Era- • 245 to 66 million years ago – many geological and life changes during this era • Divided into periods: • Triassic – mammals 1st appeared – the 1st were small mouse-like and 1st dinosaurs appeared • Jurassic – began 208 million years ago – Age of Dinosaurs – figure 17.9 on page 407 • Cretaceous – began 144 million years ago – the spread of the mammals and the evolution of flowering plants such as oak, fig, and elm trees • Geological changes – the hypothesis of continental drift – how the continents move or plate tectonics

  18. Earth’s Geologic Time Table • Cenozoic Era- • “The Age of Mammals” • 66 million years ago – we live in this era • mammals flourish, evolution of mammals into modern groupings, primates spread across the planet about 60 million years ago– humans 1st appeared 200,000 years ago

  19. Extinction’s • Billions of species have become extinct in the 3.5 billion years that life has existed on Earth • The fossil record indicates several mass extinctions • The 1st was the extinction of the dinosaurs during the Cretaceous period about 66 million years ago – many scientists believe this extinction was the result of a crash of a massive asteroid on the Earth changing the atmosphere by massive amounts of dust in the air • Estimates of approximately 2/3rds of all species died during this extinction

  20. Extinction’s

  21. The Origins of Life • Spontaneous Generation- The idea that life was produced from nonliving matter

  22. The Origins of Life Notes • Francesco Redi’s Experiments- disproves spontaneous generation - • Redi’s hypothesis: Only flies can produce more flies • Redi’s steps: • Rotten meat is placed in 2 experimental jars and 1 control jar • Cloth was placed over 1 experimental jar • A cork was placed over 1 experimental jar • The control jar, with no covering, filled with fly maggots because flies landed on the meat and laid their eggs • The cloth covered jar had maggots on the meat as the eggs were laid on the cloth and fell through • The corked experimental jar had no fly maggots

  23. Redi’s experiment

  24. The Origins of Life Notes • Louis Pasteur and Biogenesis- • Pasteur setup an experiment in which only air was exposed to a nutrient broth – no microorganisms were allowed to get to the broth – his experiment showed that spontaneous generation does not happen because no organisms grew in the nutrient broth • Pasteur came up with the concept of: • Biogenesis: living organisms come only from other living organisms – the cornerstone of Biology

  25. Louis Pasteur and Biogenesis

  26. Origins: The Modern Ideas • Simple organic molecules formed from the primitive atmosphere: prokaryotes • The primitive atmosphere was composed of water vapor, hydrogen, methane, and ammonia and a 1930’s Russian scientist Alexander Oparin proposed that life began in the early oceans when the suns energy and light energy (lightening) hit the atmospheres chemical components reactions occurred producing simple organic compounds

  27. Origins: The Modern Ideas • Oparin imagined the reactions occurred in the atmosphere and then rain poured down bringing the organisms with it – forming a primordial soup • In 1953 American scientists Stanley Miller and Harold Urey tested Oparins experiment by simulating the primordial scenario - • Water vapor circulated with ammonia, hydrogen, and methane that was subjected to electrical sparks of “lightening” the mixture was repeatedly heated and cooled, simulating night and day

  28. Origins: The Modern Ideas • After 1 week they found that the mixture develop amino acids, sugars, and other organic compounds • The formation of complex organic compounds and pre-cells: eukaryotes- • Miller and Urey’s experiments showed that heat and amino acids will link together to form small proteins – leading scientists to speculate that life began in small pools of water where amino acids were concentrated

  29. Miller-Urey experiment

  30. Origins: The Modern Ideas • Scientist Sydney Fox showed how heating amino acids could produce cells – a protocell – a large ordered structure that carries out the activities associated with life: growth, division, and metabolism

  31. How Did Life Begin?Beliefs and Theories: • Divine Origins- • Life was created by a supreme being – this is a belief not a scientific theory • Extraterrestrial Beginnings- • Life was brought to Earth by meteorites – due to some organic material found in meteorites

  32. How Did Life Begin?Beliefs and Theories: • Primordial Soup- • Ancient oceans filled with organic molecules and atmospheric elements, and heat from planet reactions – caused reactions among amino acids forming the 1st primitive life forms to evolve • Bubble Theory- • Primordial reactions occurred in bubbles of lipids (fats) where methane and ammonia could have been present – molecules were kept close together and more chemical reactions took place – developing complex molecules that we call cell – the building block of life

  33. The Evolution of Cells • Heterotrophic prokaryotes- • Were the 1st true cells • Scientists speculate 1st forms of life were prokaryotes that were anaerobic organisms that required no oxygen for existence, especially since the atmosphere had little to no oxygen • These prokaryotes were heterotrophs because they obtained their food from their surroundings

  34. The Evolution of Cells • Heterotrophs evolved into autotrophs – autotrophs can make their own food – these organisms were similar to archaebacteria – they live with little sunlight and oxygen – found in sulfur springs and deep sea events

  35. The Evolution of Cells • Photosynthesizing prokaryotes- • Autotrophs evolved into photosynthesizing prokaryotes (who produce oxygen as a by-product of respiration) • These new photosynthetic prokaryotes began putting large amounts of oxygen into the atmosphere • The event began the Oxygen revolution about 2.8 billion years ago which is seen in the fossil record

  36. The Evolution of Cells • Ancient storms with lightening caused the oxygen to be converted into ozone – resulting in the protective ozone layer – preventing harmful UV rays from destroying the newly formed life – thus paving the way for more complex organisms to evolve

  37. Charles Darwin and Natural Selection • Fossils interested scientists in evolution • The fossil record has helped form the basis of early evolutionary concepts • These fossils convinced scientists that life slowly changed over time or evolved • 18th century scientists proposed many ideas but only the theory proposed by Charles Darwin has become accepted • Charles Darwin is considered to be the founder of modern evolutionary theory

  38. Charles Darwin and Natural Selection • Darwin studied the natural world during the voyage of the Beagle • In 1831, at 21 years old, Darwin began his 5-year journey as a naturalist – his job was to collect, study, and store biological specimens discovered on the journey • He traveled from England to South America, around Capehorn and north to the Galapagos Islands and west through the South Pacific to Australia

  39. Charles Darwin and Natural Selection • Darwin’s observation in the Galapagos • Darwin noted in his observations of Galapagos animal inhabitants that they were unique to the islands yet similar to species seen in other parts of the world • By the end of his trip Darwin was convinced evolution occurs – that species change over time • Yet he still wanted to test his ideas before he could explain how such changes occur

  40. Charles Darwin and Natural Selection • Darwin completed his studies in England • Upon Darwin’s return to England in 1836, he started a 22 year study of his collections and began conducting experiments • Darwin was also interested in an essay written stating that the human population was growing faster than the food supply

  41. Charles Darwin and Natural Selection • Applying this to his studies – he knew many organisms reproduced many offspring but large numbers of species did not cover the Earth, so Darwin concluded that there must be a struggle for existence among individuals • Competition for food and space, escape from predators, and the need to find shelter • Only some individuals survived long enough to reproduce – but which ones?

  42. Charles Darwin and Natural Selection • Darwin began experiments where he would select certain variations in his pigeons and breed the pigeon’s for the desired trait • These breeding experiments are called – artificial selection

  43. Charles Darwin and Natural Selection • Darwin’s explanation for evolution • Darwin wanted to know if there was a force in nature similar to artificial selection • Darwin examined his data and began to form his idea of evolution by natural selection

  44. Charles Darwin and Natural Selection • Natural selection is a mechanism for change in populations that occurs when organisms with favorable variations for a particular environment survive, reproduce, and pass these variations or traits on to the next generation • Organisms with less favorable variations are less likely to survive to pass on their traits • Each new generation will be made up of organisms that have the favorable trait • Darwin published his findings in 1859 in his book “On the Origin of Species by Natural Selection”

  45. How natural selection works • Over population of a species. Example: 1000’s of fish eggs laid at once • Within any population individuals will show slight variations. Examples: in fishes: color, fin and tail size, and speed • Individuals with favorable traits in their environment are most likely to survive than individuals with less favorable variations. Example: fishes whose skin color blends in with its surroundings will less likely fall prey to predators • Surviving individuals will breed and produce offspring with the variations that allowed them to survive predator attacks

  46. Components of Natural Selection

  47. Evolution: Areas of Disagreement • Gaps in the fossil record: fossil history does not give a complete history of life on Earth • Many gaps are present • Transitional fossils are absent • Limits of accuracy in radiometric dating: not all samples produce consistent results • Inconclusive origins of life: we absolutely do not know how life began • Similarities among embryos: many structures are shared by different organisms during early fetal development but are differentiated later – Some people interpret this data to indicate that all organisms are related – others do not

  48. Natural Selection and Adaptations • Structural adaptations arise over many generations • The mole rat adapting larger teeth and claws to be able to dig deeper holes and avoid predators • Structural adaptations that change the structure of body parts:

  49. Natural Selection and Adaptations • Example: can develop quickly in a geological perspective of a minimum of 100 years • Mimicry: structural adaptation that provides protection for an organism by enabling it to copy the appearance of another species • Example: the coral snake and milk snake • Camouflage: a structural adaptation that enables an organism to blend in with its surroundings • Example: the insect – the walking stick – looks like a branch or stick on a tree

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