Life on Earth and on other worlds

1. Prehistory: physical conditions for the Universe to be life-friendly Life on Earth Chances for extraterrestrial life Search for other civilizations – are we alone in the Universe? Life on Earth and on other worlds

2. Do we live in a special universe?? • Change of physical constants by a very small amount would • render impossible the life in the universe as we know it • Adding or subtracting just one spatial dimension would make • the formation of planets and atoms impossible • Life as we know it needs a universe which is large enough, flat, • homogeneous, and isotropic

4. Anthropic Principle We observe the universe to be as it is because only in such a universe could observers like ourselves exist. That is, selection effects would say that it is only in universes where the conditions are right for life (thus pre-selecting certain universe) is it possible for the questions of specialness to be posed. This is a solution, but can we do better?

5. Supernatural explanation Do we need a supernatural force? How, and whether is it possible to cognize a real world? Newton, Galileo, Kant, and many others: Faith and scientific reasoning should not interfere

6. When any form of belief (religious, ideological etc. ) tries to solve scientific problems, the progress is stopped, and only bad thing happen: From inquisition (Giordano Bruno, Galileo) to prosecution of genetics, ban on theory of evolution, quantum mechanics, etc. Beliefs and rational thinking are two complementary parts of human personality, but they should not replace one another

7. Our local country is nothing special (ancient travelers) Planet Earth is nothing special (Copernicus) Milky Way galaxy is nothing special (Hubble) Our part of the Universe is nothing special Self-reproducing Universe Eternal Big Bang and ensemble of universes History of science teaches us that there is nothing special in the place we live Linde, Vilenkin

8. Landscape of the multiverse Planck scale: Planck Length Planck Mass Planck density 1094 g/cm3

9. Life on Earth Organization. All living things are organized and structured at the molecular, cellular, tissue, organ, system, and individual level. Organization also exists at levels beyond the individual, such as populations, communities, and ecosystems. Maintenance/Metabolism. To overcome entropy (the tendency of a system to become more disorganized and less complex), living things use energy to maintain homeostasis (i.e., maintain their sameness; a constant, structured internal environment). Metabolism is a collective term to describe the chemical and physical reactions that result in life. Growth. Living things grow. The size and shape of an individual are determined by its genetic makeup and by the environment. Response to Stimuli. Living things react to information that comes from outside or inside themselves. Reproduction. Individuals reproduce themselves. Life also reproduces itself at the subcellular and cellular levels. In some instances, genetic information is altered. These mutations and genetic recombinations give rise to variations in a species. Variation. Living things are varied because of mutation and genetic recombinations. Variations may affect an individual's appearance or chemical makeup and many genetic variations are passed from one generation to the next. Adaptation. Living things adapt to changes in their environment.

10. Physical basis of life on Earth: the carbon atom! Carbon can form long, complex, stable chains of atoms Another shared property is that the proteins found in present-day organisms are fashioned from one set of 20 standard amino acids. These proteins include enzymes (biological catalysts) that are essential to development, survival and reproduction.

11. Key property: information storage and duplication Replication agent: nucleic acids RNA and DNA The genetic code specifies the amino acid sequences of all the proteins each organism needs. More precisely, the instructions take the form of specific sequences of nucleotides, the building blocks of nucleic acids. These nucleotides consist of a sugar (deoxyribose in DNA, and ribose in RNA), a phosphate group and one of four different nitrogen-containing bases. In DNA, the bases are adenine (A), guanine (G), cytosine (C) and thymine (T). In RNA, uracil (U) substitutes for thymine. The bases constitute the alphabet, and triplets of bases form the words.

12. Information Storage and Duplication All information guiding all processes of life are stored in long spiral molecules of DNA (Deoxyribonucleic Acid) Basic building blocks are four Amino acids: Adenine, Cytosine, Guanine, and Thymine Information is encoded in the order in which those amino acids are integrated in the DNA molecule.

13. Processes of Life in the Cell Information stored in the DNA in the nucleus is copied over to RNA (ribonucleic acid) strands, which acts as a messenger to govern the chemical processes in the cell.

14. Duplication and Division In the course of cell division, the DNA strands in the nucleus (chromosomes) are duplicated by splitting the double-helix strand up and replacing the open bonds with the corresponding amino acids Process must be sufficiently accurate, but also capable of occasional minor mistakes to allow for evolution.

15. When the earth formed some 4.6 billion years ago, it was a lifeless, inhospitable place. A billion years later it was teeming with organisms resembling blue-green algae. How did they get there? How, in short, did life begin?

16. The Origin of Life on Earth • Life develops into more complex forms through gradual evolution, spanning many thousands of generations. • Life began in the sea as single-celled creatures. • Those as well as early multi-celled creatures had no hard parts to leave fossils. Earliest, microscopic fossils date back ~ 4 billion years.

17. Two advances of the 19th century In one advance Louis Pasteur discredited the concept of spontaneous generation. He offered proof that even bacteria and other microorganisms arise from parents resembling themselves. He thereby highlighted an intriguing question: How did the first generation of each species come into existence? The second advance, the theory of natural selection, suggested an answer. According to this proposal, set forth by Charles Darwin and Alfred Russel Wallace, some of the differences between individuals in a population are heritable. When the environment changes, individuals bearing traits that provide the best adaptation to the new environment meet with the greatest reproductive success. Consequently, the next generation contains an increased percentage of well-adapted individuals displaying the helpful characteristics. In other words, environmental pressures select adaptive traits for perpetuation. Repeated generation after generation, natural selection could thus lead to the evolution of complex organisms from simple ones. The theory therefore implied that all current life-forms could have evolved from a single, simple progenitor - an organism now referred to as life's last common ancestor.

18. Prehistory Previous stars supplied heavy elements Our Solar System has been formed with the Sun – sufficiently long-lived star One of the planets, the Earth, formed at a distance from the sun where conditions were favorable and the necessary chemical ingredients were available (note illustration's infalling comet and dust) for the origin of life.

19. The prebiotic earth: first billion years Vigorous chemical activity is represented by the heavy clouds, which were fed by volcanoes and penetrated both by lightning discharges and solar radiation. The ocean received organic matter from the land and the atmosphere, as well as from infalling meteorites and comets. Here, substances such as water, carbon dioxide, methane, and hydrogen cyanide formed key molecules such as sugars, amino acids, and nucleotides. Such molecules are the building blocks of proteins and nucleic acids, compounds ubiquitous to all living organisms. A critical early triumph was the development of self-replicating RNA molecule, which directed biological processes and preserved life's "operation instructions" for future generations.

20. The Miller Experiment Miller Experiment in 1952: Simulating conditions on Earth when life began ~ 4 billion years ago: Experiment produced some of the fundamental building blocks of life: amino acids, fatty acids, and urea. Water (oceans), primitive atmosphere gases (hydrogen, ammonia, methane), and energy from electric discharges (lightning).

21. The Origins of Life on Earth (3) • Miller experiment shows that basic building blocks of life form naturally. • Amino acids and other organic compounds naturally tend to link up to form more complex structures. • Early oceans on Earth were probably filled with a rich mixture of organic compounds: the “Primordial Soup” • Chemical evolution leads to the formation and survival of the most stable of the more complex compounds.

22. Extraterrestrial Origin of Life on Earth • Alternative theory: Most primitive living entities transported to Earth in meteorites or comets. • Some meteorites do show traces of amino acids. • Theory of extraterrestrial origin of life is currently untestable.

23. Early evolution of life Most of life's history involved the biochemical evolution of single-celled microorganisms. We find individual fossilized microbes in rocks 3.5 billion years old, yet we can conclusively identify multicelled fossils only in rocks younger than 1 billion years. The oldest microbial communities often constructed layered mound-shaped deposits called stromatolites, whose structures suggest that those organisms sought light and were therefore photosynthetic. These early stromatolites grew along ancient seacoasts and endured harsh sunlight as well as episodic wetting and drying by tides. Thus it appears that, even as early as 3.5 billion years ago, microorganisms had become remarkably durable and sophisticated!

24. Advanced life: last 500 million years Trilobites – among the first complex organisms

25. The Origin of Life on Earth (2) ~ 1/2 billion years ago, in the Cambrian Period, the diversity and complexity of life on Earth dramatically increased “Cambrian Explosion” Best-known fossils from the Cambrian period: Trilobites. All known fossils from the Cambrian period are from sea creatures. No traces of life on land until ~ 400 million years ago.

26. Geologic Time In geologic terms, higher life forms, in particular mammals and humans, have evolved only very recently. Humans have existed for only ~ 3 million years.

27. Three Questions About the Evolution of Life 1) Could life originate on another world if conditions were suitable? Miller experiment etc. indicate: probably yes. 2) Will life always evolve toward intelligence? If intelligence favors one species over another: probably yes. 3) How common are suitable conditions for the beginning of life? Investigate conditions on other planets and statistics of stars in our Milky way

28. Habitable planet should have a stable temperature regime and a liquid to mix the essential building block elements together (carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur, and transition metals like iron, chromium, and nickel). The planet should have a solid surface to concentrate the building block elements together in the liquid on top. The more concentrated the solution of water and molecules is, the more likely the molecules will react with each other. If the molecules were fixed in a solid, they would not be able to get close to each other and react with each other. If the molecules were in a gaseous state, they would be too far apart from each other to react efficiently. Though the reactions could conceivably take place, they would be rare! The planet should also have enough gravity to keep an atmosphere.

29. Life in Our Solar System Other planets or their moons are unlikely to have ever provided suitable conditions for life. Most promising candidate: Mars. Claimed traces of microscopic fossils may well be regular mineral formations in the rock. Meteorite ALH84001,0 probably originated on Mars. Possibly some evidence of past life on Mars, but questionable.

30. Jupiter’s Family of Moons Over two dozen moons known now; new ones are still being discovered. Four largest moons already discovered by Galileo: The Galilean moons Io Europa Ganymede Callisto Interesting and diverse individual geologies.

31. Europa: heated internally, therefore the surface is soft No vertical surface features can survive! Surface is smooth as a skating rink Fig. 18-10a, p.389

32. The Interior of Europa Europa is too small to retain its internal heat Heating mostly from tidal interaction with Jupiter. Core not molten No magnetic field. Europa has a liquid water ocean ~ 15 km below the icy surface.

33. Titan • About the size of Jupiter’s moon Ganymede. • Rocky core, but also large amount of ice. • Thick atmosphere, hiding the surface from direct view.

34. Titan’s Atmosphere Because of the thick, hazy atmosphere, surface features are only visible in infrared images. Many of the organic compounds in Titan’s atmosphere may have been precursors of life on Earth. Surface pressure: 50% greater than air pressure on Earth Surface temperature: 94 K (-290 oF) methane and ethane are liquid! Methane is gradually converted to ethane in the Atmosphere Methane must be constantly replenished, probably through breakdown of ammonia (NH3).

36. 200 billion stars in the Milky Way Planetary systems are common However not all stars and all planets are suitable for life! How Many Of Them Are Out There?

37. Amount of hydrogen fuel Lifetime = Rate of energy loss Lifetime T ~ M/L ~ 1/Mp-1 = 1/M2.5 ; p ~ 3.5 T ~ 3x108 years M = 4M;

38. “Good” stars should live long: 0.5 to 1.4 solar masses Binary stars are probably excluded Only metal-rich Population I stars contain heavy elements

39. G and K stars are most suitable

40. Requirements for Life in Other Planetary Systems • Planetary systems are probably common. • Stable orbit around the star consider only single stars. • Time for evolution consider only F5 or less massive stars. • Moderate temperatures Life zone around the star

41. The Drake Equation Factors to consider when calculating the number of technologically advanced civilizations per galaxy: Nc = N*· fp · nLZ · fL · fl · FS Most of the factors are highly uncertain. Possible results range from 1 communicative civilization within a few dozen light years to us being the only communicative civilization in the Milky Way.

42. Other factors: global catastrophe mass extinctions

44. Mass extinctions: once every ~ 100 million years Asteroid or comet of 10 km size?

46. 150 known impact sites on the earth Diameters from 50-70 m to 200 km

47. Barringer crater, Arizona 49,000 yr old Iron meteorite of size 50 m, mass 300,000 ton Impact velocity 11 km/sec Over 30 tons of fragments found Fig. 19-12b, p.426

48. The K-T Event and the Cretacious-Tertiary mass extinction 65 million years ago Sixty-five million years ago, about 70 percent of all species then living on Earth disappeared within a very short period in what is termed the Cretaceous-Tertiary Mass Extinction---commonly known as the K-T Event (K is used to denote the Cretaceous period rather than C to avoid confusion with other periods such as the Cambrian). Among the species that disappeared were the last of the dinosaurs. The cause of this and other sudden species extinctions has long been an important and controversial topic. In 1980, physicist Luis Alvarez and coworkers reported finding a very high concentration of the element iridium in the sedimentary clay layer laid down at the time of the K-T extinction. On Earth, iridium is very rare in the crust because it was concentrated in Earth's core when it was largely molten. However, chondritic meteorites often still have the primordial solar system abundances of these elements. This led Alvarez et al to suggest that a chondritic asteroid 10 kilometers in diameter that struck the Earth in the K-T period would contain enough iridium to account for the worldwide clay layer iridium enhancement, and that this meteor impact could also have triggered dramatic climatic changes that produced the K-T extinction.

49. K/T boundary clay layer (Italy) Places where the sediments were found

50. Further evidence: Sites near the Brazos River in Texas show a thick layer of unusual sediment immediately underneath the iridium layer. This sediment was formed by a massive tsunami (tidal wave), caused by the impacting object. Sites in Beloc, southern Haiti, also show tsunami debris together with large quantities of ejected material such as shocked quartz and tektites. spherules tectites Shocked quartz