Online Quiz Chapter 16 Due Wednesday at 11:59PM. Online Quiz Chapter 7 Due Wednesday at 11:59PM. Online Quiz Chapter 8 Due Wednesday at 11:59PM

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1 Reminders I 1 Online Quiz Chapter 16 Due Wednesday at 11:59PM 2 Online Quiz Chapter 7 Due Wednesday at 11:59PM 3 Online Quiz Chapter 8 Due Wednesday at 11:59PM 4 Online Quiz Chapter 18 Due Friday at 11:59PM 5 Read Chaps: 16, 7, 8, 18 1

2 Reminders II 6 Evaluations: Do Them! 7 Final Exam Wed Dec 16, 8:00am covers Chaps 5, 6, 7, 8, (some 9), 15, 16, 18 + cumulative 8 Clicker Grades in D2L 2

3 Missing Clickers 3

4 Lecture 40 What is the likely nature of Extraterrestrial Life? 4

5 What is Life? I Property of Matter Describable by Physics and Chemistry? The most distinguishing characteristics of matter that we call alive are the abilities to reproduce and to evolve. A flame can ignite other flames (thus reproducing itself), but it cannot evolve into other sorts of oxidation reactions, such as iron rust. But we have extensive evidence from fossils that life has been able to transform itself continuously, 5

6 What is Life? II producing the abundant examples of living matter that surround us, from amoebae and blue-green bacteria to whales and redwoods. What is life made of? Eighty-three stable elements exist in nature, ranging from hydrogen (the lightest) to bismuth (the heaviest). Just four of these elements hydrogen, oxygen, carbon, and nitrogen comprise more than 95 percent (by weight) of the matter that we call alive! 6

7 What is Life? III These four elements are the most abundant elements in the universe, except for two of the inert gases (helium and neon), which do not form chemical compounds. The four most abundant elements composing the Earth are silicon, iron, magnesium, and oxygen. In other words, the composition of living matter resembles the composition of the stars more closely than the composition of the planet on which we find ourselves. 7

8 What is Life? IV The large amount of hydrogen and oxygen in living organisms follows naturally from the high percentage of water that all life contains, and this percentage seems reasonable because water is so abundant at the Earth s surface. But carbon and nitrogen, though abundant in stars, are relatively rare on Earth, far less abundant than silicon or iron, for example. The concentration of carbon and nitrogen in living matter demands an additional explanation. This explanation 8

9 What is Life? V hinges on the chemical properties of carbon and nitrogen atoms. 9

10 History of Origin of Life on Earth I 1 Four and a half billion years ago, the Earth had a primitive atmosphere consisting of carbon- and nitrogen-containing gases, plus a few percent hydrogen and no free oxygen, above a rocky surface on which there were abundant reservoirs of water. This atmosphere may have been lost and reconstituted several times as a result of comet and asteroid impacts and continued outgassing. 10

11 History of Origin of Life on Earth II 2 During the next few hundred million years, the Earth s surface gradually accumulated a widely dispersed primordial soup of organic compounds and phosphates, the result of the energy provided by solar ultraviolet radiation, lightning discharges, and other sources. Erosion of the rocky surface of our planet probably provided the phosphates, but these and some of the organic material may also have arrived in comets and meteorites. 11

12 History of Origin of Life on Earth III 3 Additional compounds formed within the soup as the result of continuing chemical reactions, aided by local sources of heat, water runoff, and evaporation and / or freezing. 4 This in turn led to the formation of polymers, possibly on the surfaces of clays. 12

13 Early atmosphere I Early Atmosphere was probably less reducing Gas Giants have atmospheres that are highly reducing CH 4, NH 3, H 2 O, H 2 but UV leads to CO 2, CO, N 2, H 2 O (mildly reducing) Nitrogen N 2 is 78% of earth s atmosphere 13

14 Early atmosphere II comes from outgasing from subsurface rock life on earth helps explain the persistance of Nitrogen in our atmosphere lightening produces NO, (fixing the nitrogen) rain washes NO into the soil, thus Nitrogen should disappear denitrifying bacteria break the nitric oxides apart, returning N to the atmosphere 14

15 Miller Experiment 15

16 Stanley Miller 16

17 Early Atmosphere 17

18 Necessities for Life Needs to have something that can make complex molecules in which energy can be stored (on earth: Carbon) Needs a solvent to maintain chemical equilibruim, regulate temperature, and provide a material in which nutrients can float (on earth: water) 18

19 Water makes up 95% of Jellyfish 19

20 Formation of Life Organic Material Forms In hydrothermal vents In the atmosphere In interstellar space Washed into streams, ponds, tidal pools Water provides shield from UV! 20

21 Water is self-shielding 21

22 Early Life Incoming material (comets, asteroids, meteorites) rich in organics early life was probably chemical rather than photosynthetic 22

23 Early Life in Reducing Atmosphere 1 ammonia molecule + 2 methane molecules = 1 glycine molecule water molecules 5 hydrogen molecules + energy NH 3 + 2CH 4 + 2H 2 O + energy C 2 H 5 O 2 N + 5H 2 23

24 Early Life in Mildly Reducing Atmosphere 3 hydrogen cyanide molecules + = 1 glycine molecule 2 water molecules cyanamide molecule energy 3HCN + 2H 2 O + energy C 2 H 5 O 2 N + CN 2 H 2 Needs ABSENCE OF Free Oxygen Life creates the oxygen of the present atmosphere 24

25 Clicker Question Do you think that the Terrestrial Climate is warming (a) Yes (b) No (c) No opinion 25

26 Clicker Question Do you think that Climate Change is driven by human activities (a) Yes (b) No (c) No opinion 26

27 The Case for Carbon Carbon can form bonds with four other Hydrogen atoms for example: Methane CH 4 Others Cannot: Oxygen makes just 2: H 2 O and H 2 O 2 Nitrogen: NH 3 (ammonia) and N 2 H 2 (hydrazine) 27

28 Oxygen Compounds 28

29 Periodic Table 29

30 What about Silicon? I Si-Si bonds about half the strength of C-C bonds Thus Si-Si bonds more easily broken than C-C bonds C-H and C-O bonds about as strong as C-C bonds Si-H and Si-O bonds stronger than Si-Si bonds 30

31 What about Silicon? II Thus long chains of Si-Si-Si materials unstable Si-O polymers possible, but they are very stable (rocks) 31

32 Difficulty of Silicon I Silicon has strong affinity for Oxygen Even if Si exists under strong reducing conditions (atmosphere full of hydrogen) SiH 4 doesn t form until about 1000K Below 1000K makes SiO 2 Example Jupiter Atmosphere Primarily Hydrogen Contains: NH 3, PH 3, AsH 3, CH 4, GeH 4, and H 2 O But no: SiH 4! 32

33 Difficulty of Silicon II O/C 20 therefore Si will end up in SiO 2 CO 2 desolves in H 2 O, easily breaks up into C+O but SiO 2 is hard to dissolve Also CO 2 is gaseous to -75 C SiO 2 doesn t become a gas until 2000 C! 33

34 Solvents Solvent Temp for Range of Liquid State Temp Water 0 to 100 C 100 C Ammonia -78 to -33 C 45 C Methyl Alcohol -94 to 65 C 159C 34

35 Heat Capacity Solvent C V (cal/g) Latent Heat (cal/g) Water 1 C 595 Ammonia 1.23 C 300 Methyl Alcohol 0.6 C

36 Case for Water Water Expands on freezing ponds freeze from the top down Water is polar Other polar molecules dissolve in it But non-polar ones (oil) do not Means we can have cell membranes 36

37 Summary Life forms on earth in the presence of an atmosphere different from that today If all the life on earth were destroyed, in this picture it would not start again Easy to make amino acids, but not so easy to actually produce DNA and RNA Like to see early life before it evolved Mars 37

Chapter 19. History of Life on Earth

Chapter 19. History of Life on Earth Chapter 19 History of Life on Earth Opening Activity Draw a picture of what you think Earth s first life form may have looked like and label the parts of the organism. Content Objectives I will be able