9PTYS_206_origin_life

9PTYS_206_origin_life - PYTS/ASTR 206 – Origins of life:...

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Unformatted text preview: PYTS/ASTR 206 – Origins of life: Here and elsewhere 1 Announcements HW6 due now for 50% credit Last in-class activity today Comments on the final No ‘office hours’ today as we’ve run out of assignments Ask for grades via email Meetings about course material for anyone interested • We can set up a time by email • Or come talk to me after the lecture PYTS/ASTR 206 – Origins of life: Here and elsewhere 2 Origins of life: Here and elsewhere PTYS/ASTR 206 – The Golden Age of Planetary Exploration Shane Byrne – shane@lpl.arizona.edu PYTS/ASTR 206 – Origins of life: Here and elsewhere 3 In this lecture… Requirements for life Carbon compounds Energy Liquid water Building a habitable planet Galactic location Planetary location Planetary companions The Early Earth Plates and Volcanoes Impacts Evidence for early oceans Life on Earth Earliest evidence Rise of Oxygen Life outside Earth? Mars, Europa & elsewhere PYTS/ASTR 206 – Origins of life: Here and elsewhere 4 What’s “Alive”? There’s no formal definition Common characteristics proposed Homeostasis Organization Metabolism Growth Reproduction Including adaptation Response to stimuli PYTS/ASTR 206 – Origins of life: Here and elsewhere 5 Requirements Three basic building blocks Carbon Energy Liquid water PYTS/ASTR 206 – Origins of life: Here and elsewhere 6 Organic molecules require carbon Manufactured in nuclear reactions in big stars Carbon is an abundant material But not on the Earth! Life gathers and concentrates sparse elements like carbon PYTS/ASTR 206 – Origins of life: Here and elsewhere 7 Why is carbon so useful? Up to four bonds Can bond in many different ways H H C H Bonds with: Hydrogen Nitrogen Oxygen H H H H H H C C C C H H H H H H C C C C H H C C H PYTS/ASTR 206 – Origins of life: Here and elsewhere 8 Organic molecules based on carbon can become huge Non-linear and complex Organic chemistry allows for very complicated reactions to take place Reactions that lead to life And caffeine…. PYTS/ASTR 206 – Origins of life: Here and elsewhere 9 Luckily this stuff is everywhere Complex hydrocarbons have been detected in giant molecular clouds PYTS/ASTR 206 – Origins of life: Here and elsewhere 10 …and they’re not that hard to make on Earth Miller-Urey experiment Put basic compounds together Meant to simulate the atmosphere of the early Earth Add some electrostatic discharges You get complex organic molecules… PYTS/ASTR 206 – Origins of life: Here and elsewhere 11 Carbon is rare on Earth But common further out in the solar system Carbonaceous meteorites Dark material that coats icy bodies Easy to deliver carbon compounds to the early Earth Iapetus PYTS/ASTR 206 – Origins of life: Here and elsewhere 12 Increasing complexity costs energy Growth & reproduction need energy Life needs an energy source Energy is available from Stars Internal heat sources Radioactivity • Earth-like planets Contraction • • Jupiter Helium rain on Saturn Differentiation PYTS/ASTR 206 – Origins of life: Here and elsewhere 13 Liquid water is an essential component Medium to suspend reacting material Gets molecules in contact with each other Can dissolve many compounds easily Radiation protection But it’s pretty rare in our solar system Limited to Earth’s surface Interiors of some of Jupiter’s Moons Along with Titan (and maybe Triton) Ganymede PYTS/ASTR 206 – Origins of life: Here and elsewhere 14 Building a habitable planet Galactic position plays a role Central locations have many stars Manufactures elements like carbon …but… Close stellar passages disrupt planetary systems Stars in the outskirts are sparse Solar systems are safe …but… Not as many heavy elements produced Fewer planetary systems PYTS/ASTR 206 – Origins of life: Here and elsewhere 15 You need the right kind of star Supermassive stars burn up their fuel and explode They live only a few million years Not enough time to develop life Or even planets Very small stars last almost forever Long after the galaxy is a cold dead place these little stars will still be shining feebly They don’t supply much solar energy to planets The planetary systems also tend to be low-mass PYTS/ASTR 206 – Origins of life: Here and elsewhere 16 A planet must lie in the habitable zone Temperature range where liquid water is stable on the surface Depends on how bright the star is Carful… if you get too close you’ll be tidally locked Fry one side of the planet Freeze the other PYTS/ASTR 206 – Origins of life: Here and elsewhere 17 Giant planets are helpful They can get rid of a lot of the small bodies Fewer impacts More conducive to life …but… Giant planet migration can also cause more impacts Late heavy bombardment in out solar system PYTS/ASTR 206 – Origins of life: Here and elsewhere 18 Giant planets can also be a menace… Giant planets migrate into the inner solar system Pretty much wreak any Earth-like planets in that region PYTS/ASTR 206 – Origins of life: Here and elsewhere 19 This happened to many systems PYTS/ASTR 206 – Origins of life: Here and elsewhere 20 Earth Mars, Earth Earth, Venus, Mars All start with CO2 and water in their atmosphere CO2 and water goes into rocks Rocks recycled by plate tectonics Mars No plate tectonics–CO2 stuck in rocks Venus Water not stable as liquid Venus CO2 stays in atmosphere Rock cycle Runaway icehouse Runaway greenhouse PYTS/ASTR 206 – Origins of life: Here and elsewhere 21 The Early Earth We know life arose in at least one place… The solar system is half way out in the galaxy Safe from other stars Enough raw material to build planets Earth orbits a mediocre star Big enough to power life Small enough to last a long time Earth is in the habitable zone Liquid water is common We have a nearby friendly gas giant planet – Jupiter Cleared away many small bodies Didn’t migrate close to the sun and kill us all Earth seems to have struck the balance in regulating atmospheric CO2 Plate tectonics PYTS/ASTR 206 – Origins of life: Here and elsewhere 22 Earth initially forms and differentiates Radioactive elements power geologic activity Large moon-forming impact Earth mostly molten Inner solar system gets cleaned up over the first 100 million years Many big collisions No atmospheres or oceans are stable Initial crust is oceanic crust PYTS/ASTR 206 – Origins of life: Here and elsewhere 23 Volcanoes produce secondary atmosphere of steam and CO2 Continental fragments produced from reprocessing of oceanic crust Earth cools water forms oceans CO2 starts to dissolve Venus-style greenhouse avoided Hadean and Archaean geologic periods PYTS/ASTR 206 – Origins of life: Here and elsewhere 24 Plate tectonics swaps hot mantle material for cold crustal material Important way for Earth to lose heat More heat to lose in the early Earth so plate tectonics was probably more active Many smaller plates Ocean-ocean plate interactions Subduction Produces continental rock PYTS/ASTR 206 – Origins of life: Here and elsewhere 25 Starting with only oceanic crust we can manufacture continental crust as ocean arc islands These continental fragments get shuffled around Eventually they stick together to form the first continents PYTS/ASTR 206 – Origins of life: Here and elsewhere 26 How long did this take? New work on analysis of Zircon crystals Virtually indestructible Survive long after the original rock is eroded away Dated back to 4.4 Gyr ago Earth formed 4.5Gyr ago Results Formed with continental rocks i.e. plate tectonics was operating Formed in the presence of water i.e. oceans already existed PYTS/ASTR 206 – Origins of life: Here and elsewhere 27 Large impacts still occurring Vaporizes oceans Recovery time of 1000s of years Still not a good time for life – but things start to calm down Late heavy bombardment occurred 3-8 to 4 billion years ago Lunar crater record – Jupiter’s inward migration Existing life? Probably could not survive… Oldest evidence for life Rise of Oxygen Hadean Plate Tectonics PYTS/ASTR 206 – Origins of life: Here and elsewhere 28 Life on Earth Finding ancient evidence of life on Earth is complicated… Fossils only cover the most recent periods Because recent rocks are well preserved Because older life was not multicellular There aren’t many Archaean rocks left… PYTS/ASTR 206 – Origins of life: Here and elsewhere 29 Earliest evidence for life is geochemical Carbon has many isotopes 12C, 13C, 14C Isotope ratios of living things is very distinctive These ratios are found in rocks in Greenland – Age 3.85 billion years ago End of late heavy bombardment period – 3.8 billion years ago Life appeared very quickly once conditions permitted it Oldest evidence for life Hadean Plate Tectonics PYTS/ASTR 206 – Origins of life: Here and elsewhere 30 First physical fossil evidence comes later Stromatilites – 3.5 billion years ago Colonies of cyanobacteria – used CO2 for energy and emit Oxygen Precipitate calcium carbonate which gets fossilized PYTS/ASTR 206 – Origins of life: Here and elsewhere 31 The Archaean saw the start of life At least the life that stuck around That life had an unexpected effect… PYTS/ASTR 206 – Origins of life: Here and elsewhere 32 Life basically terraformed the Earth But almost wiped itself out in the process Appearance of oxygen was a major crisis The stromatilites and bacterial mats used CO2 and produced Oxygen ~2.7 billion years ago O2 started coming out of the oceans And oxidizing everything in sight Created banded iron formations These organisms used to dominate the globe Now a new kind of Oxygen-using lifeform has taken over PYTS/ASTR 206 – Origins of life: Here and elsewhere 33 Life outside the Earth Two main candidates Mars Ancient wet climate Warmer temperatures in the past A rock record that goes back to the early solar system Europa A current-day liquid ocean In contact with a rocky core PYTS/ASTR 206 – Origins of life: Here and elsewhere 34 Jupiter’s tidal flexing pumps heat into Europa’s interior Keeps the ocean liquid Probably drives volcanism in the inner rocky core PYTS/ASTR 206 – Origins of life: Here and elsewhere 35 In the case of Mars the chances of current life are pretty slim Surface is chemically very oxidizing Destroys organic molecules Water is not liquid (usually) Temperatures are low (not much energy to drive life) …but… Chances of life on early Mars are quite good Warmer climate Liquid water Viking lander one had a biological experiment package PYTS/ASTR 206 – Origins of life: Here and elsewhere 36 We have an interesting sample of ancient Mars here on Earth Meteorite ALH0084001 Timeline 4.5 billion years ago Rock solidifies Oldest rock we have 3.6-4 billion years ago Rock was fractured Carbonate minerals form in cracks Bacteria live in the rock Rock gets ‘fossilized’ 16 million years ago Rock is blasted off Mars by an impact 13 thousand years ago Rock lands in Antarctica 25 years ago Someone finds it… PYTS/ASTR 206 – Origins of life: Here and elsewhere 37 What was in this meteorite? Organic compounds on the fractures But this stuff is commonplace Carbonate globules Looks a lot like things terrestrial bacteria produce Magnetite grains Look a lot like remains of terrestrial magnetic bacteria “Fossils” Look like fossilized bacteria Except they’re about 1000 times smaller than terrestrial bacteria People aren’t so sure now… Most people don’t consider this conclusive Lots of debate, but we need new information to solve this one PYTS/ASTR 206 – Origins of life: Here and elsewhere 38 In this lecture… Prerequisites for life Organic compounds, energy and liquid water Prerequisites for a habitable planet Galactic location, Star-type, position in the habitable zone and friendly gas giants The Early Earth Unsuitable for life until after late heavy bombardment Early life appeared very fast Life changed Earth’s atmosphere to be oxygen rich Astrobiology Europa’s subsurface ocean may harbor life today Ancient Mars may have harbored life Next: Final next week – on Tuesday Reading Chapter 28 to revise this lecture PYTS/ASTR 206 – Origins of life: Here and elsewhere 39 Notes on the final: TUESDAY MAY12TH AT 11AM Questions will be multiple choice (usual scan-tron) Topics About 50% recycled questions from the mid-terms (word for word) Everyone can get a high mark on this Most of the remaining 50% will be on material covered since the second midterm A handful of new questions will cover the entire course This test will be longer than the mid-terms - 1.5 hours About 75 questions ...
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