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Lecture-29 (PDF) Life in the Universe Orin Harris and Greg Anderson Department of Physics & Astronomy Northeastern Illinois University Spring 2021 c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 1 / 95 Overview Dating Rocks Life on Earth How Did Life Arise? Life in the Solar System Life Around Other Stars Interstellar Travel SETI Review c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 2 / 95 Dating Rocks Zircon Dating Sedimentary Grand Canyon Life on Earth How Did Life Arise? Life in the Solar System Life Around Dating Rocks Other Stars Interstellar Travel SETI Review c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 3 / 95 Zircon Dating Zircon, (ZrSiO4), minerals incorporate trace amounts of uranium but reject lead. Naturally occuring uranium: • U-238: 99.27% • U-235: 0.72% Decay chains: • 238U −→ 206Pb, τ =4.47 Gyrs. • 235U −→ 207Pb, τ = 704 Myrs. 1956, Clair Camron Patterson dated the Canyon Diablo meteorite: τ =4.55 Gyrs. c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 4 / 95 Dating Sedimentary Rocks • Relative ages: Deeper layers were deposited earlier • Absolute ages: Decay of radioactive isotopes old (deposited last) oldest (depositedolder first) c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 5 / 95 Grand Canyon: Earth History from 200 million - 2 billion yrs ago. Dating Rocks Life on Earth Earth History Timeline Late Heavy Bombardment Hadean Shark Bay Stromatolites Cyanobacteria Q: Earliest Fossils? Life on Earth O2 History Q: Life on Earth How Did Life Arise? Life in the Solar System Life Around Other Stars Interstellar Travel SETI Review c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 7 / 95 Earth History Earth Forms (4.6 Ga) Oxygen in Atmosphere Impact Forms Moon (4.5 Ga) Late Heavy Bombardment Isotopic Evidence (3.8 Ga) Stromatolites (3.45 Ga) Hadean Archean Proterozoic Phanerozoic 5 4 3 2 1 0 Billions of years ago c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 8 / 95 Earth History Earth Forms (4.6 Ga) Oxygen in Atmosphere Impact Forms Moon (4.5 Ga) Late Heavy Bombardment Isotopic Evidence (3.8 Ga) Stromatolites (3.45 Ga) Hadean Archean Proterozoic Phanerozoic 5 4 3 2 1 0 Billions of years ago Paleozoic Mesozoic Cenozoic c OSD C P TR J K Pg N 550 450 350 250 150 50 Millions of years ago c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 8 / 95 Timeline for Early Life on Earth Life arose on Earth soon after the end of late heavy bombardment. • 4.6 billion years ago (Ga) - earth forms • 4.2, 4.4 Ga - evidence of oceans (detrital zircon) • 4.1–3.8 (3.85-3.82) Ga – late heavy bombardment • 3.8 Ga – Isotopic % BIF evidence from Greenland • 3.5, 2.7 Ga – Stromatolites and other fossils. • 2.3 Ga – The great oxygenation event • 2.0 Ga – Evolution of Cells with Nuclei (Eukaryotes) • 1.2 Ga – Evolution of complex multicellular organisms • 0.5 Ga – Cambrian explosion c 2012-2021 G. Anderson., O. Harris Universe: Past, Present & Future – slide 9 / 95 Hadean Earth c Don Dixon Fossil Stromatolites Modern stromatolites: Shark’s Bay Cyanobacteria “blue-green algae” • The fossil record for early life (Stromatolites) goes back 3.5 Gyrs (disputed) [2.7 Gyrs (undisputed). • Early photosynthesis created a great oxygenation event 2.4 Gyrs ago. • Cyanobacteria obtain their energy through photosynthesis, and pro- duce oxygen as a byproduct. • By releasing oxygen into the atmo- sphere, Cyanobacteria allowed for the evolution of more complex life- forms on Earth. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 13 / 95 Q: Earliest Fossils? According to fossil evidence, how far back in time did life on Earth exist? A) About 65 million years B) About 545 million years C) About 1.0 billion years D) > 2.7–3.5 billion years or more c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 14 / 95 Q: Earliest Fossils? According to fossil evidence, how far back in time did life on Earth exist? A) About 65 million years B) About 545 million years C) About 1.0 billion years D) Fossil stromatolites in Australia are 3.5 Ga. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 14 / 95 History of Atmospheric Oxygen • Before 2.3 Ga levels of atmospheric oxygen were to low to sustain aerobic life. • By 0.5–0.6 Ga, atmospheric oxygen was plentiful enough to support complex multicellular life. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 15 / 95 Q: Life on Earth You have a time machine with a dial that you can spin to send you randomly to any time in Earth’s history. If you spin the dial, travel through time, and walk out, what is most likely to happen to you? A) You’ll be eaten by dinosaurs. B) You’ll suffocate because you’ll be unable to breathe the air. C) You’ll be consumed by toxic bacteria. D) Nothing: you’ll probably be just fine. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 16 / 95 Q: Life on Earth You have a time machine with a dial that you can spin to send you randomly to any time in Earth’s history. If you spin the dial, travel through time, and walk out, what is most likely to happen to you? A) You’ll be eaten by dinosaurs. B) You’ll suffocate because you’ll be unable to breathe the air. C) You’ll be consumed by toxic bacteria. D) Nothing: you’ll probably be just fine. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 16 / 95 Dating Rocks Life on Earth How Did Life Arise? Origin of Life on Earth Phylogenetic tree Hydrothermal Vents How did life arise? Miller-Urey How Did Life Arise? Experiment (1953) RNA World Hypothesis pre-cells DNA DNA Strand Evolution Natural Selection Peppered Moth Q: Natural Selection? Life in the Solar System Life Around Other Stars Interstellar Travel c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 17 / 95 Origin of Life on Earth Last Universal Common Ancestor (LUCA): • All life on Earth shares a common ancestry. • We may never know exactly how the first organism arose, but laboratory experiments suggest plausible scenarios. Possibilities include: • tidepools • hotsprings • deep sea hydrothermal vents c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 18 / 95 Hydrothermal Vents Some lines of evidence, including DNA sequencing, suggest the first life earth may have been an extremophile which lived in extremely high temperatures near deep sea hydrothermal vents. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 20 / 95 How did life arise? 1. Simple organic molecules form 2. Replicating molecules (RNA?) evolve and begin to undergo natural selection. 3. Replicating molecules become enclosed within cell membranes. 4. Some cells evolve modern metabolic processes. 5. Multicellular life evolves c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 21 / 95 Miller-Urey Experiment (1953) Stanley Miller & Harold Urey’s U. Chicago experiment to simulate conditions on early Earth: Ingredients for Primor- dial Soup: • Water (H2O) • Methane (CH4) • Ammonia (NH3) • Hydrogen (H2) Shocked, heated cooled, ...produced Amino acids: the building blocks for protiens. Modern versions of this experiment have produced even more builing blocks for life. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 22 / 95 RNA World Hypothesis The first life on earth used RNA to store genetic information and to catalyze chemical reactions. • Discovery of Ribozymes - RNA can catalyze chemical reactions. • Formation of long RNA strands may catalyzed by clays, salty ice water c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 23 / 95 pre-cells Clay minerals catalyze formation of membranes around RNA. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 24 / 95 Deoxyribonucleic acid (DNA) Molecule that encodes the genetic instructions for all living cells. Double helix composed of the nucleotides. Nu- cleotide = nucleobase + deoxyribose sugar + phosphate group. Nucleobases: • Guanine (G): C5H5N5O • Adenine (A): C5H5N5 • Thymine (T): C5H6N2O2 • Cytosine (C): C4H5N3O c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 25 / 95 Evolution Evolution: The change in the inherited characteristics of biological populations over successive generations.” • All life on earth has decended a common ancestor. • The fossil record shows evolution has occurred through time. • Darwin’s theory of natural selection tells us how this evolution occurs. • This theory was supported by the discovery of DNA: our genetic information is stored in DNA, evolution proceeds through mutations. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 27 / 95 Natural Selection Charles Darwin (1809–1882), The Origin of Species (1859). Natural Selection: • Variations exists within all populations of organisms. • More offspring are produced than can possibly survive. • Individuals with certain traits are more likely to reproduce. • Over time the population evolves. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 28 / 95 Evolution of the Peppered Moth Peppered Moth (Biston betularia): Studied for 200 years. Two morphs: typica (light) vs carbonaria (dark). In the UK, over time mostly light −→ mostly dark −→ mostly light. c 2012-2021G.Anderson.,O.Harris Universe:Past,Present&Future – slide 29 / 95 Q: Natural Selection? Which of the following best describes natural selection? A) It is the idea that organisms with genetic traits that improve their ability to reproduce are more likely to pass those traits on to future generations. B) It is the idea that the strong survive and the weak die off.
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