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2nd midterm Complete Study Guide

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Western University
Astronomy 2021A/B

Astronomy second midterm study guide Chapter 6 – The origin and evolution of life on Earth When did life begin? - Stromatolites o Living: colonies of bacteria living in outer layer of sedimentary rocks  Sediment mixed with microbes that use photosynthesis to gain energy  Those on bottom use organic compounds left as waste for energy o 3.5 byr old rocks: almost identical layered structure  If we find a rock with fossil from 3.5 billion years ago we know life was before that time - Microfossils o Very rare o Oldest microfossils are 3.5 billion years old (life may have existed before this)  Studies suggest life originated 3.5 – 3.0 billion years ago o Reside in sedimentary rock - Isotopic Evidence o Carbon – 12 atoms are common and carbon – 13 are more rare (1/89) o Living organisms and fossils show less carbon-13 than inorganic material 13 o Some rocks older than 3.85 byr show the low C abundance Evolutionary relationships - Living fossils (living creatures) can show relationships o Ex. Chimps and humans - Slow investigation o Dna sequencing is slow and painful - DNA sequencing uses order but not dating (can’t determine time but only order) Stromatolitic, microfossil, and isotopic evidence points to life originating 3.85–3.5 Byr ago: • shortly after end of Heavy Bombardment ~3.9 Byr ago Where did life begin? - Unlikely on land o Solar UV radiation: protection today by ozone (O3) o But no atmospheric oxygen in the early Earth - In water: no problem, UV absorbed effectively - Shallow ponds o First evidence from Miller-Urey experiment o Recent evidence: incorrect atmospheric content - Thermophiles (deep sea and underground environments are most likely candidate) o DNA evidence shows early thermophiles o Have advantage of more chemical energy o Deeper sea vents better protected against bombardment How did life begin? - Life is made up of organic molecules made from chemical reactions - Early organic chemistry had no oxygen o Beneficial as oxygen destroys many organic compounds - Miller-Urey experiment o Small gas flasks were used to simulate chemical conditions on early earth o One had water to represent the sea and was heated to produce water vapour. o Methane and ammonia were mixed to represent the atmosphere o Flowed into second flask where sparks created energy for chemical reactions o Glass was cooled so it condensed and rained back into first glass. o The water eventually turned brown and after a chemical analysis it showed that there were amino acids and organic molecules in the water o WE NOW KNOW MIXTURE OF METHANE AND AMMONIA WAS NOT REPRESENTATIVE OF ATMOSPHERE - Alternative sources of amino acids o Extraterrestrial: amino acids are abundant in meteorites o Deep sea vents: abundant chemical energy & protected from UV - Chemical reactions near the ocean surface, near deep sea vents and from space played a role in shaping early life From Chemistry to biology • Organic soup of amino acids – Has to be the initial step, however the amino acids formed • Short strands of RNA (needs enzymes to replicate but enzymes can’t be made without RNA) – Required physical catalysts: clay or other minerals • Clay refers to silicate materials • Oldest zircon grains show clay was around 4.4 billion years ago 1. Clay catalyzes formation of RNA strands up to a few abses 2. RNA strands peel away from clay and fold 3. Folded RNA molecules attach to make longer RNA strands 4. Longer strands perform more catalysis eventually leading to self replication – Some had to be self-replicating (some could partially catalyze their own replication) – DNA arose from an RNA world • RNA materials canbe easily contained in Spontaneous lipid membranes  “pre-cells or vessicles” – Protect chemicals and allow faster reactions (increases chance of self replication) – Isolated from outside which allows enzymes and RNA to be concentrated (faster reactions) • Slow initial natural selection – Gradual increase of complexity – Fast mutation but slow natural selection at first • Rapid natural selection within pre-cells – Complexity  risk  faster natural selection – Probably the stage when DNA formed and took over Could Life have migrated to Earth? - Idea called Pansperima - For: o Fact: amino acids found in meteorites - For a living microbe to arrive on earth it would have to survive 1. Impact that blasts it off a. Possible 2. Time in harsh environment (space) - Unlikely a. No atmosphere or water b. Solar and stellar radiation 3. Plunge through atmosphere a. Possible - Easy formation of life o Life could have formed on Earth, but also elsewhere in the solar system o Life was then transported to Earth, before life on Earth had a chance to form Early Microbial Evolution - Looked like modern bacteria or archae o Lacked nuclei and other complex structures found in eukarya - All life must have been Anaerobic: it does not require molecular oxygen o We are aerobic organisms (we can’t survive without oxygen) - First microorganism where chemoautotrophs o Got carbon from carbon dissolved in oceans and energy from chemical reactions - Had limited enzymes which meant a faster mutation rate. This led to faster evolution o Fossil evidence of photosynthetic organisms prove this - Thermophiles were favourited: got energy from hydrogen, iron and sulfur Cyanobacteria - Exist today (blue-green algae) o Earliest fossils resemble modern cyanobacteria - Release oxygen in photosynthesis o Many microbes went extinct when oxygen was created as they attack bonds of molecules - Oxygen is highly reactive: would disappear from the atmosphere in a few million years o To maintain oxygen, it therefore needs to be replenished constantly o Today: living creatures consume most of the Oxygen - Early Earth: inorganic reactions, mainly rusting iron, suffice, and for a long time prevented the rise of Oxygen - Banded iron formations (23 byr old) suggest very low atmospheric oxygen (less than 1% of today) - Rise of Oxygen began about 2 byr ago - Evidence for Oxygen at today’s levels: only 0.2 byr ago Earliest Eukarya - Evidence o Earliest known fossils: 2.1 byr ago o First, earlier eukarya developed folding in their membranes ultimately leading to a cell nucleus o Second, they absorbed small bacteria creating a symbiotic relationship: where both organisms benefit from the other being there  Evidence of symbiosis comes from mitochondria (energy from ATP) and chloroplasts (energy from photosynthesis)  Both have their own DNA and can reproduce on their own proving theat they were once free roaming bacteria Cambrian Explosion: - All 3 domains of life were established 2.1 billion years ago - Animals classified by phyla o Chordata (internal skeletons): reptiles and mammals o Arthropoda (segmented, external skeleton): insects, crab and spiders o Altogether modern animals: ~30 phyla - Cambrian explosion (began 542 million years ago) o Diversiy of life began (Phylas began appearing) o Long after the appearance of eukaryotes o No similar diversification since then - Why? o Sudden rise in oxygen o Significant increase in genetic complexity o Climate: emerging from snowball Earth episodes o No efficient predators Colonization of land • Microbes – Colonized where it was Easy to find water and UV protection on land • Larger organisms – Remained in the oceans longer, particularly animals • No protective ozone layer (protects against UV) • Only microbes could live on land – Need to draw water from the soil but energy from sunlight – Plant colonization of land began ~ 475 myr ago • Algae – DNA: plants evolved from algae – Algae  plants in small pools during periods of dryness? • Carboniferous period – Animals followed plants to land within 75 myr – Large forests ~ 360 myr ago  coal K-T Event (65 million years ago) • Cretaceous-Tertiary (KT) transition: – Dinosaurs disappear “instantaneously” 65 myr ago • Meteorite event – Luis and Walter Alvarez: found sediments on boundary rich in iridium (Ir), like in meteorites (rare on earth) – Found KT Iridium the same as KT boundary, all around the world – Would have taken a meteorite 10-15 km in diameter to distribute it all around the earth • Evidence for the impact 1. High abundances of osmium, gold and platinum 2. Shocked quartz: formed at high temperature and pressure 3. Spherical rock droplets: molten rock solidifies in air 4. Soot (some sites): widespread fires 5. 200 km crater in Yucatán peninsula: 10 km meteorite • Caused a Mass extinction – ~10 hydrogen bombs – Tidal wave up most of low-lying North America – Forest fires worldwide  harsh winter  plants die  lack of food – Acid rain  kill life in the oceans too – 99% of all living died, 75% of all species became extinct Other Mass extinctions • Multiple mass extinctions – At least 5 big ones – Many smaller ones – Event like KT every ~100 myr – Sick earth hypothesis: volcanism lead t climate change and ultimately extinction – Nearby supernova explosions also every ~ 100 myr • Release cosmic and gamma rays (destroy earths ozone layer) – Magnetic reversals every few million years remove cosmic-ray protection of the magnetosphere • Earth’s ozone layer fluctuates allowing more Ultraviolet rays. These can cause major mutations and lead to extinctions • Evolution – Catastrophes create opportunities, not just disaster – May have more effect than gradual evolution Continuing Impact Threat - Impact objects o Meteor: small (<1 cm), ~ 25 million per day, burn in atmosphere o Fireball (not UFO): medium (10 cm  1 m), explode in the atmosphere o Meteorite: large (> few m), vaporizes solid rock, leaving a crater o Tunguska meteorite (1908): <30 m, energy of several atomic bombs, sound heard round the globe, no crater (comet?) - Future o Probability declines rapidly with size o Currently able to detect threat, but not divert it (question is not whether one will occur but when?) Primate evolution • Adaptation to tree life – Limber arms – Eyes close together  stereoscopic vision – Eye-hand coordination • Parental care – Need  longer rearing time  more complex systems – Hand down experience  life past menopause • Common ancestor – We did not evolve from chimpanzees and gorillas • Common DNA – Chimpanzees and humans share 98% of their genome (closest relatives) – Ardi lived 4.4 million years ago and Lucy 3.2 million years ago • Skulls that look like modern humans date back 100,000 years – Myths: there is no missing link in human evolution and humans are all the same species regardless of race Emergence of Humankind - Numerous hominid species - Shared existence o Neanderthals: coexisted with us until 35,000 yr ago (cause of extinction unknown) Cultural and Technological evolution • Biological evolution – Slow random mutations, no significant evolution in 40,000 years • Cultural evolution – Faster and accelerating – Agriculture and written language: tens of thousands of yearsr – Industrial revolution: 200 years – Breeding: intentional selection • Technology evolution – Information technology on exponential growth – Medicine: counter to natural selection • Genetic engineering – Already taking place in agriculture – Top down approach is rearranging bits and pieces of existing organisms vs building one from scratch • Craig venter is doing this Chapter 7: Searching for life in Our Solar System Environmental requirements for life 1. Building Blocks of life - Environment that any kind of life can survive in (not just humans) - Oxygen, carbon, hydrogen and nitrogen make up 96% of living organisms o Hydrogen and helium are most common elements in the universe o If condensation and accretion occurs then we can expect worlds to contain these elements o Some organic compounds can only be formed in an atmosphere or an ocean or in space  Atmosphere and ocean are reasonable requirements 2. Energy for life - Sunlight: o Decreases as the inverse square distance o Example: if you put leaf on world twice as far from the sun as earth is, then it would only receive one fourth as much energy as a leaf on earth. (1/2^2 = ¼) - Electrical: o Lightning in atmospheres - Chemical: o Abundant, but needs mixing in atmosphere or liquid o Earth: plenty of water and atmosphere o Mars and Venus: still enough internal heat for surface or subsurface chemical reactions o Jovian moons: plenty of ice and tidal heating in the ones closest to the planets, e.g., Io and Europa 3. Water - Alternative liquids at colder temperatures: o Ammonia (NH ):3-78C  -33 C o Methane (CH )4 -182C  -164 C o Ethane (C 2 6: -183C  -89 C o Saltwater freezes slightly below 0 (seawater is -2) - Main advantages of water: 1. Wider and higher range of temp for which it is liquid 2. Solid water floats 3. Charge separation of water molecules allows for chemical bonds - Density decreases with decreasing temperature below 4C  floating Ice o Ice is less dense than liquid water - Water distributes electrical charge better o One side of molecule has a negative charge and th eothe rhas appositive charge (Called polar molecules) o Affects how water dissolves (very easily) - Does 3 main things: 1. Dissolves organic molecules, making them available for chemical reactions in cells 2. Allows for transport of chemicals into and out of cells 3. Involved directly in metabolic reactions in cells Environmental requirements for habituality 1. Source of molecules to build living cells 2. Source of energy to fuel metabolism 3. Must have a liquid medium, most likely water, for transporting molecules of life a. Most stringent requirement (hard to meet) Moon and Mercury • Small • No atmosphere • No volcanism so no outgassing and weak gravity which means gasses can escape easily • No liquids • Moon: has ice at the bottom of polar craters that are perpetually in shadow • Mercury: – Daytime temperatures of 425 Celsius – Nighttime temperatures of -150 Celsius – Close to the Sun, so little original water – Water from bombardments hard to keep (never in liquid form) – High density: giant early bombardment removed mantle and crust, where most water would have been Venus - Sister planet to earth - Hell of the Solar System o Temperature: 470C (850F) o Pressure: 90 atmospheres o Atmosphere also contains concentrated sulfuric acid and other harmful chemicals - Runaway greenhouse effect o Atmosphere: 96% CO because there is no way to remove it 2 o Oceans: too hot today for liquid water o Plate tectonics: apparently none today - Past life on Venus? o Oceans around 4 byr ago o Cratering shows the surface to be ~1 byr old (volcanism Mars - Mars cooled down - May have liquid water underground because of internal heat Jupiter + Saturn - Composition: solar - No solid surface - Water at a depth ~100 km - Strong winds and vertical circulation: no stable life at any layer of the atmosphere - Large buoyant creatures: could avoid circulation, but how would they be formed? - Other Jovian planets (Saturn, Uranus and Neptune): same problems o Uranus and Neptune have outer cores of water methane and ammonia  Potential zones of habitability Small moons, Asteroids and Comets - Large moons have potential - All: too small to keep liquid water - Comets (also Pluto and Eris): in permanent freeze o Those in Kuiper belt and oort cloud - Complex organic molecules: are found in both asteroids and comets - Small moons, e.g., moons of Mars: similar to asteroids Spacecraft exploration - We have sent robotic spacecraft to all eight planets as well as many moons asteroids and comets o New horizons is on route to pluto - Flyby: flies by world and continues on its way o Least energy  lowest cost o Gravitational boost to reach other planets o Short duration o Can obtain very high resolution images o Can measure magnetic fields or sample interplanetary dust - Orbiter: orbits world studying allowing for longer observations o More energy  higher cost o Longer duration - Probes and landers: probes atmosphere by flying through it or lands on planet o Probes: death-throe information from orbiter  Probe sent down to collect info before it crashes or breaks o Landers: often capable of roaming - Sample return: spacecraft comes back to earth carrying sample o Blast-off  highest energy o So far only from the Moon (Soviet Union) Chapter 8: Mars - William Herschel (1784) o Most famous astronomer of his time  Discovered Uranus  Catalogued double stars and nebulae  Reinvented the hypothesis that nebulae were made of stars, i.e., galaxies (without knowing about Kant)  Measured rotation of the planets  Discovered Martian day of 24 hours 37 minutes o Mars fantasies  Mars has a atmosphere  Thought everything had inhabitants  They enjoy l
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