MOD B - The History of Life on Earth.docx
MOD B - The History of Life on Earth.docx

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University of British Columbia
Earth and Ocean Sciences
EOSC 116
Louise Longridge

Early Life 1/27/2013 7:54:00 PM Early Origins  Universe: 12-14 billion years old  Originated from the big bang  Earth and solar system formed about 4.5-4.6 billion years ago (Ga)  Water: prerequisite for life on Earth o Surface cool enough to support liquid water by 3.8 Ga The Biosphere  Biosphere: thin layer of life that surrounds the surface of the planet o Penetrates a bit into the crust and is present in the atmosphere o Interacts with the lithosphere (solid Earth), hydrosphere (liquid water), cryosphere (ice), and atmosphere (air) o Life regulates surface conditions on Earth Origins of Life on Earth  Three hypotheses o (1) Panspermia: life was brought to earth o (2) Earth-based origin: ocean margin hypothesis o (3) Earth-based origin: deep ocean hydrothermal vent hypothesis Panspermia  Organic molecules brought to Earth by impacts of extraterrestrial bodies  Life may have been transported to Earth as microbes  No evidence for either claim Earth-based Origin: Ocean Margin Hypotheses  Alexander Oparin and J.B.S. Haldane: conditions on Earth favored chemical reactions that produced organic compounds from inorganic material  Miller’s Experiment (tested the hypothesis) o Mixed gases that were thought to be constituents of the early Archean atmosphere (methane, ammonia, water, and hydrogen) o Added an electric spark to represent the turbulent Archean atmosphere o Bathed the mix in UV light o Results: 20 amino acids had formed o Criticism  Did not represent the true composition of the Archean atmosphere o Established that it is possible to produce organic molecules via abiogenic processes  Definition of “living” o Metabolism o Growth o An ability to reproduce o Evolution with changing environmental conditions  Polymerization: amino acids being brought together to form more complex molecules o Sidney Fox: evaporate seawater off a beach  amino acid chains could be returned to the ocean on the next tide o Clay helps polymerization  Clay has an electrical charge capable of attracting amino acids  Acts as a template for the formation of complex molecules Earth-based Origin: Deep Ocean Hydrothermal Vent Hypothesis  Hypothermal vent: forms when oceanic water seeps through cracks in the seafloor and is heated by magma o Water heats  less dense  rises back to the surface o Heated water passes through oceanic rocks to dissolve minerals and transport them to the surface where they are precipitated to form vents  Organic + inorganic materials have been discovered at these vents o Deep ocean may have been where life originated DNA or RNA?  DNA: deoxyribonucleic acid: contains info needed in the development and functioning of all living organisms and some viruses o Chicken and the egg problem: which came first o DNA is the blueprint of life but can only reproduce with enzymes, which require DNA to be produced in the first place…  RNA: ribonucleic acid: self-replicating  possible that earliest life on Earth may have been RNA-based, not DNA-based First Life: Primitive Heterotrophs  Earliest fossils: advanced microbes  means one of two things: o Life was brought to Earth via Panspermia at that particular time at that specific stage of development (unlikely since fossils were well-adapted to Earthly conditions) o We are missing lots of info about early life on Earth  Early life was anaerobic: don’t need free oxygen o Oxygen produced around 2.5 Ga  Early life was heterotrophic: no need to synthesize own food, find food to eat instead o Organic chemicals in the ocean were probably used for food o ATP (used for metabolism) was abundant in the oceans  Early life form was a prokaryote: organism that lacks a nucleus o Lived in oceans, fed on the organic compounds produced from inorganic stuff  Meteorite crashed into Mars that may have transported stuff to Earth 16 Ma  Life may have developed in a wet Mars and Earth o Life may have originated on Mars and been transferred to Earth on meterorites The Autotrophs  The ATP supply in the oceans depleted  Evolution of autotrophic bacteria  Autotroph: organisms that produce complex organic compounds from simple inorganic compounds and energy o Fermentation: used by autotrophs o Photosynthesis: develops later The Earliest Fossil Evidence  Found in the Australian Apex Chert (3.5 billion years) and resembles cyanobacteria (photosynthetic)  Isua Formation, Greenland o Rocks here have C-12 (signature of photosynthesis) Stromatolites  Mats of cyanobacteria (blue-green algae) that develop in shallow-water marine conditions  They trap and bind sedimentary (inorganic) grains which help form layered domes o Layers grow when the cyanobacteria grow and move upwards towards the sun  Oldest stromatolites are located in W. Australia (3.5 billion years old) Increasing Complexity  Eukaryotes: DNA contained in a nucleus (includes all life forms that are not bacteria)  Possess internal cell structures called organelles (unlike prokaryotes)  Sexual distinction: vital for the diversifying life o Prokaryotes reproduce via binary fission (make identical copies of the parent cells) o Sexual reproduction allows for variation in kids  made evolution faster  Structures that generate energy for the cell (mitochondria: animals; chloroplast: plants) have their own DNA different from that in the cell nucleus o Suggests that these energy structures once existed as independent prokaryotes o Suggests a symbiotic relationship (joined, instead of destroying each other)  Endosymbiosis  (1) Start with 2 independent bacteria  (2) One bacteria engulfs the other  (3) One bacteria now lives in the other  (4) Both bacteria benefit  (5) Internal bacteria are passed onto future generations  Earliest fossil evidence for eukaryotes: 900 million years ago in Bitter Springs Formation, Australia Evolving Earth, Evolving Atmosphere  Most significant change: Earth’s transition from no oxygen to tons of oxygen o Occurred between 2.5 to 1.8 Ga  “Great Oxygen Crisis”  Evidence o (1) Banded iron formations o (2) Uraninite (UO2) and pyrite (FeS2) o (3) Red beds Banded Iron Formations (AKA BIFs)  BIF: rocks composed of bands of chert (cryptocrystalline silica, SiO2) and other iron oxide minerals o Unique b/c under current chemical conditions of Earth’s oceans, they can’t form  Before the Great Oxygen Crisis, iron minerals were eroded from land and transported to the oceans in a reduced state o Earth’s early oceans had tons of dissolved iron o When oxygen came about, the iron would “rust” and be precipitated as iron oxide on the ocean floor Uraninite (UO2) and Pyrite (FeS2)  These two minerals were eroded from continental rocks and deposited in ocean sediments  After oxygen was introduced, they were oxidized  B/c of this, they are not found in oceanic sediments younger than 1.8 billion years old Red Beds  Iron minerals in desert sands existed in a reduced state  Color of reduced iron is green o Desert sandstone is green before oxygen is introduced o Turns red after oxidation  Source of the introduced oxygen: possibly cyanobacteria (stromatolites) o They produce oxygen as a by-product of photosynthesis Multicellular Creatures: The Rise of the Metazoans  Advantages of being multicellular o (1) You can get big and interact more effectively with the environment o (2) You live long (replace dead cells)  Earliest large body fossils: Ediacaran fossil o Over 100 species  were extinct by the early Camrbian  Early metazoans (multicellular, eukaryotic organisms) o Evidence for existence: traces of larger creatures that were moving around in ocean sediments were found  Trace fossils: evidence that organisms physically interacted with the environment o Bioturbated sediments: Sediments that were mixed or disturbed by organisms  Fossils of animal embryos and multicellular algae: preserved in Doushantuo Formation The Study So Far Years Before Present Event 3.8 billion First prokaryotes 2.5-1.8 billion Photosynthesis 2.5-1.8 billion Great Oxygen Crisis 1.4 billion Eukaryotes 600 million First metazoans Video (Stromatolites)  Extremophiles: heat-loving bacteria o Most primitive organisms on Earth o Must have existed 3.7 billion years ago o Earliest ancestors of all life The Cambrian Explosion 1/27/2013 7:54:00 PM Introduction  Cambrian Explosion: burst in innovation in creatures with hard parts  Major body plans developed and evolved into creatures we see today Life in the Cambrian  Cambrian Explosion: follows the initial radiation of metazoan life represented by Ediacaran fauna o Ediacaran fauna: soft-bodied with no skeletons  Developed metazoans with hard parts  Calcium carbonate: used to build shells  Why did the Cambrian Explosion happen? o Increase in oxygen following a glacial episode at the end of the Precambrian o Breakup of Rodinia (supercontinent) circulated nutrie
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