Origin Of Life

1. Origin Of Life

2. How Did Life Begin? • Earth was formed about 4.5 billion years ago. • It was a fiery ball of molten rock • Water vapor in the atmosphere condensed to form the oceans • Scientists think that life evolved from the oceans and has occurred over hundreds of millions of years.

3. Measuring the Earth’s Age • Scientists have been doing this for years using radiometric dating which is the estimation of the age of an object by measuring the content of a certain radioactive isotopes. • Radioisotopes are unstable isotopes that break down and give off energy in the form of charged particles (radiation)

4. This breakdown or decay results in other smaller more stable isotopes. For example: The decay of potassium-40 results in argon-40 and calcium-40

6. The radioisotope’s half-life is the time it takes for one half of a given amount of radioisotopes to decay. • Using this method scientists are able to compute how many half-lives have passed since a rock has formed.

7. Extraterrestrial Origin • Origin of life comes from outside Earth • This theory says that life might have come here from a gravity forcing a meteorite or asteroid carrying life to Earth • Simple life forms like bacteria • Evidence would be meteorites and asteroids of today

8. Divine Creation • The force of this theory that a God, Gods or Goddess created life • Life forms were fish, vegetation, birds animals, and people • Religions – Bibles – stories passed on through the generations – ethnic or cultural stories – debated for centuries.

9. Formation of the Basic Chemicals of Life • Most scientists believe that life on earth began as molecules of nonliving matter that reacted chemically during the first billion years of the earths history. • Energized by the sun and volcanic heat simple organic molecules formed more complex molecules that led to the formation of the building blocks of the first cells

10. Big Bang Theory

11. “Primordial Soup” Model • Russian scientist A.I. Oparin and British scientist J.B.S Haldane both suggested that the Earth’s oceans contained large amounts of organic molecules. • These organic molecules formed spontaneously from chemical reactions activated by solar radiation, volcanic eruptions and lightening.

12. Oparin along with an American scientist Harold Urey proposed that Earths eary atmosphere lacked oxygen. • Instead it was rich in nitrogen, N2; hydrogen, H2; and hydrogen containing gases such as water vapor, H2O; ammonia, NH3; and methane,CH4

13. Miller-Urey Experiment • In 1953 Stanley Miller, working with Urey put the gases they proposed into this device and provided electrical sparks and in a few days they found complex organic molecules in his apparatus.

14. These chemicals include the building blocks of life! • Amino Acids, Fatty Acids and other hydrocarbons

15. Reevaluating the Model • We now know that the molecules used in the experiment could not have been in abundance in early Earth. • 4 billion years ago Earth did not have a protective layer of ozone gas O3. • Without ozone protection methane and ammonia would have been destroyed and would make it impossible to make key biological molecules.

16. Lerman’s Bubble Model • In 1986 the geophysicist Louis Lerman suggested that the key processes took place in bubbles in the oceans surface. Step 1- Ammonia, methane and other gases resulted from underwater volcanic eruptions were trapped in underwater bubbles

17. Step 2 – Inside bubbles methane and ammonia needed to form amino acids might have been protected from UV radiation. Chemical reactions occurs faster in bubbles because of the concentration of reactants would be greater. Step 3 - Bubbles rose to the surface and burst releasing organic molecules into the air.

18. Step 4 – carried upward by winds the organic molecules, exposed to UV radiation and lightening provided energy for further reactions. Step 5 – more complex organic molecules were formed from further reactions fell back to the ocean as rain to begin other cycles

20. Precursers to the First Cells • Scientists disagree about the details for the origin of life • We can make simple organic molecules form spontaneously but not the larger molecules found in living cells. • However short strands of RNA have been made to form on there own in water.

21. Possible Role as a Catalysts • American scientists Thomas Cech and Sidney Altman found that certain RNA molecules act as enzymes • RNA was the first self-replicating, information-storage molecule and it catalyzed the first protiens • Such a molecule has the ability to change from one generation to the next.

22. Microspheres and Coacervates • Laboratory experiments have shown that in water lipids, when combined with other molecules can form a droplet whose surface resembles a cell membrane. • Chains of amino acids can gather into tiny droplets to form microspheres.

23. Coacervates, another type of droplet, is composed of different types, including linked amino acids and sugars

24. Scientist think that formation of microspheres might have been the first step toward cellular organization • Microspheres could not be considered true cells unless they had the characteristics of living things, including heredity

25. Origin of Heredity • Scientists disagree about the details of the origin of heredity, they agree that double stranded DNA evolved after RNA and RNA “enzymes” catalyzed the earliest proteins. • Researchers do not yet understand how DNA, RNA and hereditary mechanisms first developed.

26. The Evolution of Cellular Life • Fossils (preserved or mineralized remains or imprint of an organism) are extremely rare • The oldest fossils are microscopic photosynthetic prokaryotes called marine cyanobacteria

27. Early Earth’s atmosphere had little oxygen, marine cyanobacteria carried out photosynthesis and released oxygen into the oceans which eventually was released into the air. • Today after hundreds of millions of years the Earth’s atmosphere contains 21% oxygen.

28. Two Groups of Prokaryotes • Early in history prokaryotes evolved into two groups. • Eubacteria – prokaryotes that contain a chemical called peptidoglycan in their cell walls. An example is E. coli bacteria • Eubacteria include many bacteria that cause disease and decay.

29. Archaebacteria are prokaryotes that lack the peptidoglycan in their cell walls and have unique lipids in their cell membrane. • Chemical evidence indicates that archaebacteria and eubacteria diverged early

30. Evolution of Eukaryotes • Eukaryotes appeared about 1.5 billion years ago. • How is a eukaryote different than a prokaryote? • How did it evolve? • How do scientists believe that mitochondria and chloroplasts originated?

32. An American biologist Lynn Margulis proposed a theory of Endosymbiosis • Endosymbiosis is the theory that mitochondria are descendents of aerobic eubacteria and chloroplast are descendents of symbiotic photosynthetic eubacteria

33. Four observations to support the idea of endosymbiosis of mitochondria and chloroplasts originated from bacteria: • Size and structure – mitochondria are about the same size as eubacteria. They have inner membranes that are folded and carry out cellular respiration. Chloroplasts are about the same size as cyanobacteria and have thylakoids also where they carry out photosynthesis.

34. 2. Genetic material – Mitochondria and chloroplasts both have circular DNA that is different from that found in the host cell but similar to chromosome found in bacteria • Ribosomes – both have ribosomes that are similar size and structure as bacteria. • Reproduction – Like bacteria, mito and chloro reproduce by binary fission independently form the host cell

35. Multicellularity • Biologists classify all living things into six broad categories called kingdoms. • The two oldest kingdoms Eubacteria and Archaebacteria are made up of single celled prokaryotes. • The first eukaryotic kingdom is Protista • Protists include single celled and multicellular organisms

36. The oldest known fossils of multicellular organisms are found in rocks that are 700 million years old • Among the groups of organisms that survive today are plant-like, we know the as seaweed; red, green and brown algea. • Three of the multicellular groups evolved into the kingdoms Fungi, Plantae and Animalia • Each evolving from a protistan ancestor

37. Origins of Modern Organisms • Most animal phyla originated during a short period of time ranging from 10 to 100 million years, during the late Precambrian and early Cambrian. • This was known as the “Cambrian Explosion” • Unusual marine animals for which there are no living relatives.

38. A large collection of Cambrian fossils were found in a geological formation in Canada called the Burgess Shale. • This includes some of the strange marine animals without known relatives • The Ordovician period which followed the Cambrian period lasted from about 505 million to 438 million years ago. • Among them were trilobites are marine arthropods that became extinct about 250 million years ago

39. Mass Extinctions • The fossil record shows a sudden change at the end of the Ordovician period • About 440 million years ago a large percentage of organisms became extinct. • Extinction is the death of all the members of a species.

40. A mass extinction is when a large number of species become extinct. • This was the first of five mass extinctions that have occurred on Earth • Another mass extinction about the same size happened about 360 million years ago. • The third and the most devastating was at the end of the Permian period. • About 96% of all species living at that time became extinct.

41. About 35 million years later another less devastating mass extinction took place • Although the specific reasons for these extinctions are not known for certain most scientists believe it is from worldwide geological and weather changes were the factors. • The fifth mass extinction occurred about 65 million years ago, two-thirds of all land species including dinosaurs were extinct.

42. Formation of the Ozone Layer • The sun provides life giving light and dangerous UV radiation • In early life organisms could not leave the water which protected them from UV radiation. • About 3.5 million years ago, what began adding oxygen to the Earth’s atmosphere?

43. The ozone layer blocks the dangerous UV rays of the sun • Millions of years later enough ozone had accumulated to make Earth’s land a safe place to live.

45. Plants and Fungi on Land • The first multicellular organisms that lived on land were probably fungi living together with plants • Each possessing something the other needs • Plants can make nutrients from sunlight but cannot harvest minerals needed from bare rock • Fungi can’t make the nutrients from sunlight but can extract nutrients from bare rock.

46. Early plants and fungi had a biological relationship called mycorrhizae • Mycorrhizae exist today between fungi and roots of plants • The fungus provides minerals for the plants and the plant provides minerals for the fungus • This kind of partnership is called mutualism, which is a relationship between two species in which both benefit • Plants and fungi have been living together on land for 430 million years

47. Arthropods • 100 million years after the first plants and fungi covered the Earth the first animals successfully invaded land to eat those plants. • Arthropods have a hard outer skeleton, a segmented body, joint limbs. • Examples: lobsters, crabs, insects and spiders • Scorpians were the first land arthropods

48. The insect is a unique arthropod that evolved from the first land dwellers and have become the most plentiful and diverse group of animals in Earth’s history • Insects were the first animals to have wings • The ability to fly allows them to escape predators, search for food, find mates and nesting sites • This led to partnerships with flowering plants. • The oldest know flowering plants were about 127 million years ago

49. Vertebrates • A vertebrate is an animal with a backbone • Humans and almost all animals biger than a fist are vertebrates • About 530 million years ago the first vertebrates were a small jawless fish • Jawed fish appeared about 430 mya

50. Jaws enables fish to bite and chew their food giving them an advantage over the fish that sucked up their food. • This made the jawed fish efficient predators • Fish are the most successful living vertebrate – they make up over half of all modern vertebrates today