Origins of Life Lecture Notes PDF

TRACING EVOLUTIONARY HISTORY Origins of life UNIT 3 Lesson 12 Chapter 15  OBJECTIVES Discuss when, where and how life began Describe the prebiotic evolution was controlled by early atmosphere and climate Describe Miller-Urey Experiment Discuss The RNA-...

TRACING EVOLUTIONARY HISTORY Origins of life UNIT 3 Lesson 12 Chapter 15  OBJECTIVES Discuss when, where and how life began Describe the prebiotic evolution was controlled by early atmosphere and climate Describe Miller-Urey Experiment Discuss The RNA-world hypothesis What were the first organisms like Timeline of events Overview: Lost Worlds Past organisms were very different from those now alive The fossil record shows macroevolutionary changes over large time scales, for example: – The emergence of terrestrial vertebrates – The impact of mass extinctions – The origin of flight in birds © 2011 Pearson Education, Inc.  E ARLY E ARTH AND THE O RIGIN OF L IFE © 2015 Pearson Education, Inc. Conditions on Early Earth https://www.youtube.com/watch?v=LinWJsangs4 (3 MINUTES)  EARTH’S EARLY ATMOSPHERE 4.6 Billion Years Old Geologic evidence shows Earth formed ~4.6 BYA Early Atmosphere Probably contained CO2, CO, Nitrogen, Ammonia, Methane But, No Oxygen! (wouldn’t support life) 3.8 BYA Earth cooled enough for liquid water to form How old is this planet anyway? The Universe is probably ~13 billion years old (Big Bang Theory/Doppler Shift) Earth is ~4.6 billion years old Bombardment of Earth by rocks and ice likely vaporized water and prevented seas from forming before 4.2 to 3.9 billion years ago Earliest records of life ~3.5 to 3.8 billion years ago  When Did life Begin? Prokaryotes dominated from 3.5 to 2 billion years ago. - During this time, the first divergence occurred: Bacteria and Archaea  How did life evolve? Three theories Creationism Extraterrestrial origin (Panspermia) Spontaneous Origin Theories of early earth III. Theories Explaining the Formation of Life cont. PANSPERMIA THEORY - Life had come to earth from other planets of the universe, in the form of resistant spores. - Gk. “seeds everywhere” aka Cosmozoic Theory - Interstellar dust and comets contain organic compounds. - comets, which are largely made of water (ice) carry bacterial life across galaxies and protect it from radiation damage along the way. I. Early Theory: conditions on early Earth made the origin of life possible Spontaneous Generation (Abiogenesis)- The hypothesis that life arises regularly from non-living thing Objective: Describe the prebiotic evolution 15.2 Conditions on early Earth made the origin of life possible Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules. 2. Joining of these small molecules into macromolecules. 3. Packaging of molecules into “protobionts.” 4. Origin of self-replicating molecules. Synthesis of Organic Compounds on Early Earth Earth’s early atmosphere likely contained water vapor and chemicals released by volcanic eruptions (nitrogen, nitrogen oxides, carbon dioxide, methane, ammonia, hydrogen, hydrogen sulfide). A. I. Oparin and J. B. S. Haldane hypothesized that the early atmosphere was a reducing environment. – O2 is absent; therefore, oxidation is prevented. (O2 disrupts chemical bonds) Stanley Miller and Harold Urey conducted lab experiments that showed that the abiotic synthesis of organic molecules in a reducing atmosphere is possible.  However, the evidence is not yet convincing that the early atmosphere was in fact reducing. Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents. Amino acids have also been found in meteorites. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Primordial Soup  Primordial Soup The Primordial Soup Theory states that life began in a wam pond/ocean from a combination of chemicals that form amino acids, which then make proteins. This is suppose to happen at least 3.8 billion to 3.5 billion years ago. Basic theory by Haldane in the 1920’s The basic building blocks of life (amino acids) came from simple molecule which formed in the atmosphere (without oxygen) This was then energized by lighting and the rain from the atmosphere created “organic soup”. Lead to Miller-Urey Experiment in 1953 Deep Sea Vents Monomers Evolve Oparin/Haldane Miller /Urey Objective: Describe Miller-Urey experiment  15.2 SCIENTIFIC THINKING: Experiments show that the abiotic synthesis of organic molecules is possible In 1953, graduate student Stanley Miller, working under Harold Urey, tested the Oparin-Haldane hypothesis. Miller identified a variety of organic molecules that are common in organisms, including hydrocarbons and some of the amino acids that make up proteins.  Chemical conditions of the early Earth 1950s – Miller and Urey made a “reducing atmosphere” of H2O, H2, NH3, CH4 in a spark chamber after sparking, they found that amino acids and other organic compounds had formed designed to mimic what was thought at the time to have been Earth’s early atmosphere  Miller & Urey’s Experiment Fig. 4.7  Variations of Miller-Urey Experiment Different mixes of gases to represent atmosphere Different energy sources, like UV (sunlight) Results: ALL PRODUCE AMINO ACIDS AND COMPLEX ORGANIC MOLECULES Not as much as original experiment MUST be more sources of organic material Origin of the First Cell(s)  15.3 Stages in the origin of the first cells probably included the formation of polymers, protocells, and self-replicating RNA STEP 1: The abiotic synthesis of small organic molecules would have been the next step in the origin of life. STEP 2: Before enzymes, hot sand, clay, or rock may have helped monomers combine to form polymers. Waves may have splashed organic molecules onto fresh lava or other hot rocks and then rinsed polypeptides and other polymers back into the sea.  STEP 3 : Protocell Evolves A primitive cell-like structure that has some properties of life and that might have been precursors of cells. Made up of only 2 molecular components: RNA replicase & a fatty acid membrane Exhibit simple reproduction and metabolism & maintain an internal chemical environment (key properties of life) Extremely simple version of a cell. 32 Protobionts May Have Formed Spontaneously  STEP 4 Today’s cell The first genetic material was probably RNA, not DNA. RNA molecules called ribozymes ( ribonucleic acid enzyme , can carry out enzyme-like functions.) have been found to catalyze many different reactions For example, ribozymes can make complimentary copies of short stretches of their own sequence or other short pieces of RNA..  The origin of self-replicating molecules THE RNA WORLD HYPOTHESIS  M AJOR E VENTS IN THE H ISTORY OF L IFE 15.6 © 2015 Pearson Education, Inc.  Geologic Time Spans ↗ Earth’s History spans 4.6 billion years. ↗ Scientists have divided this large time span into smaller units called eons →eras → periods–?Epochs. ↗ Geologic Time Scale is sometimes called the calendar of Earth’s history. Eons: Precambrian: Earliest span of time Phanerozoic: Everything since Eras: Paleozoic Periods: Mesozoic Cambrian Cenozoic Ordovician Silurian Paleozoic Devonian “Age of Invertebrates” Carboniferous (Missipp. & Pennsylvanian) Permian Epochs: Triassic Paleocene Jurassic Eocene Mesozoic Cretaceous Oligocene “Age of Reptiles” Paleogene Neogene Miocene Cenozoic Quaternary Pliocene “Age of Mammals” Pleistocene Holocene We are living in the Phanerozoic Eon, Cenozoic Era, Quaternary Period, Holocene Epoch…….. PRECAMBRIAN “AGE OF EARLY LIFE” 1. Hadean Eon ↗ 4.6 to 4.0 ↗ No life ↗ Earth’s crust cools and solidifies ↗ moon forms ↗ Came from Greek word for “Hades” which means “underworld” ↗ Earth had no liquid water and was covered with many active volcanoes. 2. Archean Eon 4.0 to 2.5 billion years ago Temperature dropped ○ Earth had its first solid surface First form of life on our planet was created in the oceans 3. Proteorozoic Eon 2.5 bya to 542 mya Oxygen was added to the atmosphere First multicellular organisms evolved in water (soft bodies make evidence hard to find) 4. Phanerozoic Eon ↗ 540 myo - present ↗ Development of shells and other hard body parts https://www.youtube.com/watch?v=MYKAyIXGN 70 Table 15.6-0 15.4 The origins of single-celled and multicellular organisms and the colonization of land were key events in life’s history 5 Major Extinctions