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HOW DID LIFE EVOLVE AND WHY?. Some major episodes in the history of life. simple organism without nucleus: an organism whose DNA is not contained.

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Presentation on theme: "HOW DID LIFE EVOLVE AND WHY?. Some major episodes in the history of life. simple organism without nucleus: an organism whose DNA is not contained."— Presentation transcript:





5 Some major episodes in the history of life. simple organism without nucleus: an organism whose DNA is not contained within a nucleus, e.g. a bacterium organism with visible nuclei: any organism with one or more cells that have visible nuclei and organelles

6 1. The Earth was formed ~4.5 billion years ago 2. It took ~500 million years for the crust to solidify. 3. The oldest fossils of microorganisms 3.5 billion years old embedded in rocks in western Australia Prokaryotes dominated from 3.5 to 2 billion years ago during this time, the first divergence of life occurred: BacteriaArchaeon Bacteria and Archaeon (single-celled microorganisms with no cell nucleus and no membrane-bound organelles within their cells)

7 Fossilized evidence of bacteria  Stromatolites are fossilized bacterial mats. Many fossils of prokaryotes are found in layers that make up the prokaryotic mats.

8 4. Oxygen began accumulating in the atmosphere about 2.7 billion years ago. Cyanobacteria are photosynthetic prokaryotes that are still present today  produced oxygen. The salt crust is just like a greenhouse window!

9 Banded iron formations are evidence of the age of oxygenic photosynthesis – approximately 2 BYA

10 5. The oldest eukaryotic fossils are ~2 billion years old. Symbiotic community of prokaryotes living within larger prokaryotes.  Mitochondria and chloroplasts 6. The oldest fossils of multicellular organisms are ~1.2 billion years old.

11 7. The oldest animal fossils are ~700 million years old. Animal diversity exploded ~540 million years ago.

12 8. Plants, fungi, and animals began colonizing land ~500 million years ago. a. First plants transformed the landscape. b. Then animals were able to take advantage of new niches ( specialized area in which evolution optimizes certain species—eg. predators, parasites.  Mammals evolved 50 to 60 million years ago.

13 The Cambrian radiation of animals

14 The origin of life B. The origin of life 1. First cells may have originated by chemical evolution involving 4 steps: a. Abiotic (Non-biological) synthesis of small organic molecules (monomers)  C + H = organic molecule b. Monomers joined together to form polymers (proteins, nucleic acids) c. Origin of self-replicating molecules (inheritance of traits)  proteins and polynucleic acids d. Packaging of these organic molecules into protobionts.  Aggregates of abiotically produced molecules that maintain an internal chemical environment and exhibit some of the properties associated with life (i.e. metabolism, growth).

15 2. Evidence that supports the four-stage hypothesis for the origin of life a. In the 1920s  Abiotic synthesis of organic molecules is testable in the laboratory Hypothesis: Conditions on primitive Earth favored chemical reactions that synthesized organic compounds from inorganic precursors. These conditions were different from what is now present and include: - Reducing environment (no oxygen, but instead H 2 O, CH 4, NH 4, and H 2 ) = lots of free electrons that could be used to reduce carbon and produce organic molecules. - Energy from lots of lightning, UV radiation (no O 2 to block UV rays from the sun) and volcanic activity (heat).



18 b. Miller and Urey in 1953 i. Tested the 1920’s Oparin-Haldane hypothesis by creating conditions in which there was: - An atmosphere above warmed sea water that contained H 2 O, H 2, CH 4, and NH 3 and - Electrodes that simulated lightning. - From this setup, they obtained organic compounds such as amino acids that were collected in cooled water.

19 The Miller- Urey experiment

20 The experiment - organic molecules could be created out of inorganic molecules! So…….why don’t we see this happening in today’s world? Any organic molecules that are now formed would be used up by living organisms. If microorganisms were created from these organic molecules in the early Earth’s water bodies, this would have been an example of spontaneous generation!

21 3. RNA was probably the first hereditary material Today, genetic information is usually stored as DNA, but some organisms such as viruses use RNA to store info.

22 4. The precursors of early life are known as Protobionts. a. Protobionts form spontaneously in lab experiments from mixtures of organic molecules. b. They contain RNA that codes for metabolic proteins. These protobionts absorb food and the proteins catalyze it to make energy which can be used for growth and division to daughter cells. c. Natural selection would favor protobionts that grow and replicate. When the organic molecules in the earth’s water bodies were gone, the protobionts would “evolve” to either obtain energy by photosynthesis or predation.  It would only take the formation and evolution of one (1) protobiont to give rise to the all the different organisms we see today.

23 This 4.5 billion-year-old rock, labeled meteorite ALH84001, is believed to have once been a part of Mars and to contain fossil evidence that primitive life may have existed on Mars more than 3.6 billion years ago. The rock is a portion of a meteorite that was dislodged from Mars by a huge impact about 16 million years ago and that fell to Earth in Antarctica 13,000 years ago. The meteorite was found in the Allan Hills ice field, Antarctica, by an annual expedition of the National Science Foundation's Antarctic Meteorite Program in 1984. It is preserved at the Johnson Space Center's Meteorite Processing Laboratory in Houston.

24 C. Major lineages of life 1. At first, two kingdoms were recognized  Plants and Animals. 2. In 1969, Robert Whittaker developed a five-kingdom system  Plants, Fungi, Animals, Protists, and Prokaryotes (Monera).


26 Whittaker’s five- kingdom system

27  Energy  Medium for growth


29 Geological Time Scale Diagram: Precambrian Time (an Eon, since it is comprised of three Eras) lasting from the formation of Earth approximately 4.5 billion years ago until the first abundant fossils appeared 545 million years ago. Paleozoic Era and its 7 periods -- 545-245 million years ago when the primary Earth inhabitants were fishes. Mesozoic Era and its 3 periods -- 245-66 million years ago when the primary Earth inhabitants were reptiles. Cenozoic Era and its two periods -- 66 million years ago until present when the primary Earth inhabitants are mammals.

30 Precambrian time included almost all of Earth's first 4BY. The crust, atmosphere, and the oceans were formed, and the simplest kinds of life appeared. Primordial Earth bombarded

31 The Mesozoic Era was the Age of Dinosaurs. Plant- eating dinosaurs, such as this Stegosaurus, fed on cycads and conifers; early trees that thrived before modern flowering trees first appeared

32 The Paleozoic Era saw the development of many kinds of animals and plants in the seas and on land. The earliest land plants appeared in the Silurian Period, about 440 million years ago. The earliest land plants appeared in the Silurian Period, about 440 million years ago. Cambrian Explosion invertebrates (animals without a backbone) corals, mollusks (clams and snails) and trilobites (flat-shelled sea animals and trilobites (flat-shelled sea animals

33 The Cenozoic Era included the Pleistocene Ice Age; when glaciers swept slowly across large land areas before melting. These great masses of moving ice created a variety of landscapes in northern lands.

34 Evolution is a change in the gene pool of a population over time

35 Miller-Urey Experiment When the primordial soup (earliest organic forms) were exposed to energy, organic compounds were produced as shown by this experiment. When the primordial soup (earliest organic forms) were exposed to energy, organic compounds were produced as shown by this experiment.

36 Amino acidsAmino acids are small, highly reactive molecules composed of 20 to 30 HCNO atoms. Amino acids When amino acids link together in strings they form proteins. proteins Proteins govern chemical reaction rates and form the structural material for cell parts, which lead to complex life forms.


38 gases  compounds  proteins  simple cells  simple cells  complex cells  complex cells US!

39 The Primordial Soup Theory (Out of the Slime) The Primordial Soup Theory suggests that life began in a pond or ocean as a result of the combination of chemicals from the atmosphere and some form of energy to make amino acids, the building blocks of proteins, which would then evolve into all the living species. The Primordial Soup Theory states that life began in a warm pond/ocean from a combination of chemicals that forms amino acids, which then made proteins approximately 3.8 billion years ago. The Russian Chemist A.I. Oparin and English Geneticist J.B.S. Haldane first conceived this idea. Both developed their theory independent of each other in 1920. In this theory, the basic building blocks of life came from simple molecules which formed in the atmosphere (w/o oxygen). This was then energized by lightning and the rain from the atmosphere created the "organic soup". The first organisms would have been simple heterotrophs in order to survive by consuming other organisms for energy before means of photosynthesis. They would become autotrophs by mutation. Evidence now suggest the first organisms were autotrophs. Chemist Stanley Miller and physicist Harold Urey did their famous experiment in 1950 to test this theory. They mixed gases thought to be present on the primitive earth at that time: ammonia (NH 3 ), water (H 2 O), hydrogen (H 2 ); but no oxygen at that time.

40 A large number of complex chemical reactions is the underlying process that we call life. The main ingredients for life are: energy source supply of nutrients (building blocks) self-regulating mechanisms

41 About 3.5 million years ago, our first direct ancestor appeared, Australopithecus africanus (best fossil example), known as “Lucy”. “Lucy” represented the first physical evidence of a hominid. Hominid: any of a family (Hominidae) of upright bipedal primate mammals, which includes recent humans, as well as extinct ancestral and related forms and in some recent classifications the gorilla, chimpanzee, and orangutan. [ homin- stem of Latin homo means "human being" ]

42 Scientific classification Kingdom:Animalia Phylum:Chordata Class:Mammalia Order:Primates Suborder:Haplorrhini Infraorder:Simiiformes Parvorder:Catarrhini Superfamily:Hominoidea Family: Hominidae Genera Subfamily PonginaePonginae Pongo – orangutans Pongoorangutans Subfamily HomininaeHomininae Gorilla – gorillas Gorillagorillas Homo – humans Homohumans Pan – chimpanzees Panchimpanzees Primate: Primate: a member of an order of mammals with a large brain, and complex hands and feet; including humans, apes, and monkeys.

43 Around 13 million years ago, a tree- dwelling primate developed: primate  stereoscopic vision  high mobility (upright stance)  opposable thumbs Yo!

44 As brains became larger and more refined, the shape of the cranium evolved. The larger brain allowed humans to perform more advanced tasks which would increase their survival.


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