1. Summary for Final Last week of classes 12/10 to 12/14 Last week of classes 12/10 to 12/14 First hour (Monday): First hour (Monday): Planetarium Sky Quiz (30 pts) Planetarium Sky Quiz (30 pts) Final, Part 1 (Solar System Object Quiz, 20 pts) Final, Part 1 (Solar System Object Quiz, 20 pts)Solar System Object QuizSolar System Object Quiz Second hour (Wednesday): Second hour (Wednesday): Final, Part 3: SCANTRON Test (Form 882, #2 pencils), 70 questions from Review questions, cumulative, includes question on SGA and Planispheres (70 pts) Final, Part 3: SCANTRON Test (Form 882, #2 pencils), 70 questions from Review questions, cumulative, includes question on SGA and Planispheres (70 pts) During your Third Hour During your Third Hour Final, Part 2: Group effort on questions relating to 3 rd hour (20 pts) Final, Part 2: Group effort on questions relating to 3 rd hour (20 pts) All extra credit due by 12/14 at NOON All extra credit due by 12/14 at NOON Review Session: Friday, 7 December, 2-4 pm, here Review Session: Friday, 7 December, 2-4 pm, here

2. 2 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth Is there life beyond Earth? Great for science fiction plots, but at present there is no undeniable evidence that aliens have been here Many astronomers of the past have suggested that life existed elsewhere Kepler – thought there were inhabitants on the Moon Herschel – claimed life existed on nearly all the planets Lowell – thought he saw canals on Mars Before searching for life elsewhere in the universe we must first look at how life arose on the Earth

3. 3 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth Three recent developments have led to idea that life may not be so uncommon beyond Earth Life arose quite early in Earth’s history Laboratory experiments show that the chemical make- up of the young Earth could readily combine to form organic molecules, suggesting that life formed from naturally occurring chemistry We have discovered microorganisms which live in extreme Earth conditions which may be similar to those found on other worlds

4. 4 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth When did life arise on the Earth? After the Earth formed 4.5 billion years ago, life had little chance to survive First several hundred million years was era of heavy bombardment Theses bombardments could vaporize oceans killing any life that might have formed Studies of the craters on the Moon suggest that the heavy bombardment ended 4.2 to 3.9 billion years ago. Remarkably life may have been thriving 3.85 billion years ago, a geological blink of an eye after conditions were more hospitable

5. 5 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth Fossils and Geologic time scale The key to understanding ancient life is to look for fossils, relics of organisms which lived and died long ago. These fossils can be found under layers of sediments which are carried by rivers or lie under ocean floors. Grand Canyon show billions of years of Earth’s history Relative ages of rocks and fossils are easy to determine: each deeper layer formed earlier Radiometric dating confirms this and estimates the absolute ages of the material Based of the layering of the rocks and fossils Earth’s history can be divided into several distinct intervals or geological time scales sedimentary Geological TS Grand Canyon

6. 6 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth Fossil Evidence of Early Life Since the Earth is so geologically active, it is difficult to find rocks which are over 3 billion years old The evidence of the existence of life 3.5 billion years ago is suggestive and subtle since microscopic fossils are difficult to detect What we see today is what was left behind by ancient bacteria, rocks called stromatolites Also the increased ratio of Carbon-13 to Carbon-12 in rocks is suggestive that ancient life formed as far back at 3.85 billion years ago, just after the end of the heavy bombardment Geological TS

7. 7 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth How did life Arise on Earth? Theory of Evolution In the 19 th century, most biologists agreed that species change through time In 1859, Charles Darwin explained how life might undergo those changes based on two observations: Overproduction and struggle for survival Individual variation Conclusion: unequal reproductive success  what is often termed natural selection or survival of the fittest. Geological TS

8. 8 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth The Mechanism of Life DNA (deoxyribonucleic acid) is the genetic material of all life on Earth. It consists of 4 chemical bases: adenine (A), thymine (T), guanine (G), cytosine (C) which pair up in two long strands and wind together in a double helix DNA is self-replicating which is the key to heredity Any change (small or large) to this sequence from imperfect duplication is called a mutation Most mutations are lethal and kill the cell with the mutation But some are beneficial and these can be passed to offspring DNA

9. 9 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth The First Living Organism DNA is has the same basic chemical nature in all life Also all organisms build proteins from the same set of amino acids This suggest that all life had a common ancestor which arose some 3.85 billion years ago. The present day black smokers which thrive deep underwater at high temperatures may resemble this early form of life High temperatures may promote faster and more diverse chemistry which allows life to form quickly Looking at DNA from all life, biologists have composed a “tree of life” which suggest how the DNA changed to other types of life Consists of 3 main domains: Bacteria, Archaea, and Eukarya Tree of life Black smokers

10. 10 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth The Origin of The First Living Organism Where did this first life come from? Some experiments done in the 1950s (and since) showed a mixture of early-Earth organic molecules plus lightning can produce all the major molecules of life including amino acids and DNA bases. Strands of RNA (ribonucleic acid) which resemble single strands of DNA have been reproduced in the laboratory Many biologist presume that RNA came first followed by DNA Microscopic enclosed membranes can form which may have surrounded self-replicating RNA on the early Earth Miller-Urey Life chamber Steps to life membranes

11. 11 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth Could life have migrated from elsewhere? The idea that life started elsewhere and then came to the Earth (via meteor impacts) is called panspermia. While the prospect of life traveling and surviving through space seems difficult, we have evidence of organic molecules in meteorites and test that show microbes and survive space for years.

12. 12 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth A Brief History of Life on Earth As Earth formed, chemical reactions form the first organic molecules. After the heavy bombardment ended, the common ancestor of life formed. Life rapidly grew and diversified, but remained single cell organisms for 1 billion years. The land was still inhospitable until the ozone layer formed – this required atmospheric oxygen

13. 13 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth Nearly all of the original oxygen was released via photosynthesis from single-celled cyanobacteria some 3.5 billion years ago. For more than 1 billion years this oxygen reacted with surface rocks and little stayed in the atmosphere. Eventually, some 2 billion years ago, the oxygen began to accumulate but would not be “breathable” until just a few hundred million years ago. This allow new species (e.g. plants and animals to form) Many other species did not need oxygen or even found oxygen to be toxic cyanobacteria

14. 14 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth About 540 million years ago, tiny plants and animal organisms changed dramatically in about 40 million years and formed into all the basic plans (phyla) that we find on Earth today The dramatic change in the diversity of life is called the Cambrian explosion Dinosaurs and early arose at the same time (225 to 250 million years ago) Dinosaurs died off 65 million years ago (by a meteor impact?) and left the mammals The earliest humans formed only a few million years ago (after 99.9% of Earth’s history) Geological times

15. 15 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth What is necessary for Life to exist? While animals need moderate temperature and abundant oxygen, simpler life can life under must more extreme conditions and locations (extremophiles) Underground, high and low temperatures There seem to 3 basic requirements A source of nutrients Energy to fuel the activities of life Liquid water (the biggest constraint) Geological times

16. 16 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life on Earth While animals need moderate temperature and abundant oxygen, simpler life can life under must more extreme conditions and locations (extremophiles) Underground, high and low temperatures There seem to be 3 basic requirements A source of nutrients Energy to fuel the activities of life Liquid water (the biggest constraint) Geological times

17. 17 © Sierra College Astronomy Department Shameless Advertising Need a Science Lab Class?: Astronomy 11 – Astronomy Lab. Go outside and look at the stars and use telescopes (weather permitting). Astronomy 11 – Astronomy Lab. Go outside and look at the stars and use telescopes (weather permitting). Astronomy 14 – Astrophotography. Take pictures of stars while learning how to use a telescope. No cameras necessary (though you can bring your own if you want). Astronomy 14 – Astrophotography. Take pictures of stars while learning how to use a telescope. No cameras necessary (though you can bring your own if you want).Plus: Interdisciplinary 11 (Astro 7, Astrobiology) Interdisciplinary 11 (Astro 7, Astrobiology) Astronomy 25 – Frontiers of Astronomy Astronomy 25 – Frontiers of Astronomy

18. 18 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life in the Solar System To look for life elsewhere, we need to search for places where the basic necessities of life exist – the habitable worlds This eliminates most of world in our solar system Moon and Mercury are barren and dry Venus too hot for liquid water Jovian planets are gaseous This leaves Mars and a few of the moons orbiting Jovian planets, notably Europa Geological times

19. 19 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life in the Solar System Mars Percival Lowell thought he saw canals on Mars, but we are quite confident now that there are no civilizations on Mars. Nevertheless, we have good evidence the liquid water flowed on the Martian surface Today it contains subsurface ice which could be heated to form areas of liquid water underground Geological times

20. 20 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life in the Solar System Missions to Mars, looking for life The Viking missions took soil samples and look for chemical changes that could be attributed to biological processes 3 experiments suggested that life may be present, but also ordinary chemical reactions could have caused the same results A fourth experiment found little organic material, the opposite of what one would expect if life were present

21. 21 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life in the Solar System Pathfinder, Spirit and Opportunity studied the Martian conditions to see if life might have exsited. The Mars Express orbiter detected methane gas Methane should disappear within a few centuries due to chemical reactions So, something is supplying Mars with methane It could come from comet impacts, volcanoes, or life Volcanism seem the most like candidate Opportunity

22. 22 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life in the Solar System Martian meteorites One meteorite which landed in Antarctica 13,000 years ago and found in 1984 was clearly of Martian origin. Inside the meteorite were complex organic materials and structures which looked like nanobacteria, very small bacteria which have been discovered on Earth. These structures can also be made by chemical and geological means Contamination from being on the Earth may also explain the presence of organic materials. Inside ALH 84001 ALH 84001 nanobacteria

23. 23 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life in the Solar System Life on Europa Europa has enough tidal heating to possibly form a subsurface ocean underneath its icy crust. Life there could form like the “black smokers” on Earth. Larger life could form in the vast oceans, but energy sources are limited and this would tend to limit the size of any life there Opportunity

24. 24 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life in the Solar System Life on Ganymede, Callisto and Titan Ganymede and Callisto might have subsurface ocean, but their internal heat is small and liquid water would not be terribly abundant. Titan has no native liquid water, but an abundance of organic materials. Could life evolve from the lakes of methane? Water might be able to brought in from comets, but this would freeze eventually

25. 25 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life around other Stars Where in the Galaxy might we find life? Since technology might allow us to get surface pictures or spectra, we restrict ourselves to considering extrasolar planets with habitable surfaces So far all detected extrasolar planets (except maybe one) are gaseous giants and are unlikely to have surface life However, they may be surrounded by moons which may support life

26. 26 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life around other Stars Constraints on Star Systems A star must be stable and live long enough to allow a planet to develop life Stars greater than a few solar masses are ruled out (but this is only about 1% of all stars) A star must allow stable planet orbits Binary and multiple are much less likely to have this – about 50% of all star systems

27. 27 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life around other Stars A third constraint is a planet must form in the habitable zone. This is a region where a terrestrial type planet would have the right surface temperature for liquid water to exist. Stars less massive than the Sun have smaller zones. A star like the Sun (or more massive) would have the largest zone Even if we restricted our search to Sun-like stars, we would still have to consider billions of stars in our Galaxy Habitable zone

28. 28 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life around other Stars Finding Habitable Planets Two upcoming mission may be able spot Earth sized planets Kepler will look for transits of planets across other stars The Space Interferometer Mission (SIM) may be able to detect Earth sized planets. A decade or so from now, the Terrestrial Planet Finder (TPF) Spectra from future telescope can look for signatures of life Habitable zone spectra

29. 29 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life around other Stars Rare Earth? Some feel that an Earth type planet (with it complex type of life) is rare: Galactic constraints Too close to the galaxy’s center and the rate of supernovae are too great Too far from the center and “metal” content is too low A stellar system needs a Jupiter-like planet to sweep-out and deflect meteors that might wipe out life on Earth Galaxy Habitable zone

30. 30 © Sierra College Astronomy Department Lecture 15: Life in the Universe Life around other Stars Climate stability Plate tectonics and the carbon dioxide cycle Earth’s large moon keeps axial tilt relatively stable There are counterarguments to these, suggesting that these conditions may not too rare or would have significant effect on producing complex life Habitable zone

31. 31 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Extraterrestrial Intelligence SETI - The Search for Extraterrestrial Intelligence is trying to find signs of alien communication How many civilizations out there? The (modified) Drake Equation suggests the number of civilization we might be able to contact: # of civilizations = N HP × f life × f civ × f now Where N HP is the number of habitable worlds. f life is the fraction of these world which actually have life. f civ is the fraction of these worlds which have interstellar communications f now is the fraction of these worlds which have a civilization at the present time It is hard to know exactly what any of these numbers are at the present time Habitable zone

32. 32 © Sierra College Astronomy Department Lecture 15: Life in the Universe Interstellar Travel If one is restricted to going no faster than the speed of light, then interstellar travel will be difficult. In any event, vast new energy sources must be used to propel ship. Hydrogen scoopers Nuclear bombs or nuclear power Matter-anitmater

33. 33 © Sierra College Astronomy Department Lecture 15: Life in the Universe Interstellar Travel If there is advanced alien life out there, why haven’t we seen them? We are alone and there is no other advanced life out there Civilizations are common, but no one has colonized the galaxy because Technology prevents a widespread travel The desire to explore is unusual Civilizations destroy themselves before they can colonize the stars There is a galactic civilization, but it has not revealed itself!!!

34. © Sierra College Astronomy Department 34 THE END

35. 35 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe While there may be other Earth-like planets orbiting other stars, our search begins in our own Solar System We have seen that Earth-like conditions (pressure, temperature, atmospheric composition) are not found beyond Earth at the present time We must consider a planet’s history and changing conditions since its formation We must also have some idea what we mean by “life” Advertising other classes: Astro 7 (Astrobiology) Plus : Astro 11, 14, and 25

36. 36 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe Defining Life We need to list a few characteristics that are common to life All terrestrial life are composed of cells - organized collections of molecules enclosed in a wall-like membrane Life also reproduces itself and can change itself over time, especially if it increases its chance for survival cell

37. 37 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe Life on Earth All life is based on organic molecules, which contain carbon atoms or chains of carbon atoms combined with O, H, N, or S atoms These make up things like amino acids, nucleotides, proteins, which are used as building blocks for organisms Nucleic acids such as RNA and DNA are also essential, but are probably somewhat specialized for terrestrial life

38. 38 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe Water also seems essential for life because it make such an excellent solvent and has a high heat capacity (good for cooling down an organism) Where liquid water can exist on an Earth-like planet defines Habitable Zone Other Possibilities Silicon-based life has been proposed to be possible since silicon has many similar chemical properties to carbon However, chains of silicon atoms are less likely to form making more difficult to make complicated chemical structures Habitable Zone Habitable Zone evolution

39. 39 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe Origin of Life on Earth Fossils give us a pretty idea of the progress of life on Earth Life seemed to have developed soon after the Earth cooled as fossil bacteria date back to 3.5 billion years It is unclear whether organic material formed here on Earth or fell onto the Earth New, life forming compounds could have been produced by lightning discharges and volcanic eruptions in the primitive atmosphere of the Earth Bacteria Fossils 0.01 mm

40. 40 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe Origin of Life on Earth More complicated life arose as organic molecules gathered and formed into things like cells Given enough time more complicated life arose The conditions on Earth also became more favorable for complex life

41. 41 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe Origin of Life on Earth Also: no catastrophic event happened to wipe all the Earth’s life Jupiter is the vacuum cleaner and broom of the solar system as comets and asteroids are either destroyed or deflected away The Moon may be crucial also as it kept the Earth’s rotation tilt axis from getting too extreme

42. 42 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe Life Elsewhere in the Solar System To find a place that might have life on it, we need to search for a place that might have Earth-like conditions liquid water, solid surface Perhaps a significant atmosphere We should also consider places that may have had these conditions in the past

43. 43 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe Mars Mars has the most Earth-like conditions in the solar system Mars has seasons, polar ice caps, solid surface However, the surface is nearly airless, the temperatures are frigid -- an unlikely place for liquid water Mars may have been a more hospitable place in the past (warmer, wetter)

44. 44 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe Mars – Evidence for past life? Opportunity discovered clear evidence that liquid water once existed on Mars In 1996, a meteorite thought to have come from Mars, showed fossil like structure, and unusual amounts organic material Some astronomers dismiss this evidence as byproducts of natural inorganic processes or that the meteor was contaminated by Earth organisms Mars Fossil?

45. 45 © Sierra College Astronomy Department Lecture 15: Life in the Universe The Search for Life in the Universe Other Places Europa is another intriguing place which may harbor life Tidal stresses coming from Jupiter may allow the presence of liquid water underneath the surface Some theorist suggest, however, that the tides are not currently strong enough liquefy the icy mantle Titan is too cold for liquid water flow presently, but it atmosphere of organic molecules makes it similar to the primitive Earth conditions Enceladus (moon of Saturn) was recently discovered to have subsurface water