THE HISTORY OF LIFE ON EARTH 25.1 CONDITIONS ON EARLY EARTH MADE THE ORIGIN OF LIFE POSSIBLE

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1 THE HISTORY OF LIFE ON EARTH LOST WORLDS The Earth is ever changing. Antarctica was once a tropical paradise and the western United States was a shallow sea. Naturally occurring processes cause these changes over time CONDITIONS ON EARLY EARTH MADE THE ORIGIN OF LIFE POSSIBLE The evidence presented by analysis of extremely ancient rocks (from places like the Ediacaran Hills of Australia) and their microfossils indicate that life on Earth developed from nonliving matter. The Earth is approximately 4.6 billion years old. Its early atmosphere included these gases: CO 2, H 2 O, CO, H 2, N 2 and small amounts of NH 3, H 2 S and CH 4. There was no free oxygen in the atmosphere of early Earth. All oxygen was tied up in the structure of the various compounds that were present. The chemical conditions provided the environment that was necessary for chemical evolution to occur. Microfossils Panspermia Abiotic Synthesis Chemical Evolution Oparin + Haldane Urey + Miller Pre-Cellular Structures: Microspheres Liposomes Coacervates New technology is providing information indicating that such as interaction is much more likely to have occurred in rock or clay surfaces than directly in water. Clay is the primary choice because it contains zinc and iron ions that can act as catalysts. Laboratory research has resulted in the production of various protobionts, which are groupings of abiotically produced organic polymers. SELF-REPLICATING RNA Cech and Altman (1982) revealed that RNA was most likely the first replicating molecule. They unearthed evidence that RNA can act as a catalytic agent an enzyme. RNA molecules that act enzymatically are referred to as ribozymes. Any ancient protobionts that accessed and contained ribozymes would be able to transfer the molecules, and hence a piece of themselves, to daughter molecules/molecular masses. 9

2 25.2 THE FOSSIL RECORD DOCUMENTS THE HISTORY OF LIFE Microfossils of Clostridium species have been found in parts of Australia, South Africa and parts of Canada. Stromatolites, which are rock columns with multiple tiny layers of prokaryotes (often cyanobacteria); provide much of the evidence that prokaryotes evolved first. Fossil stromatolite reefs are found in the Great Slave Lakes (Canada), the Gunflint Iron formation of Lake Superior and the Hamlin pool of Western Australia. The first prokaryotes were probably anaerobic heterotrophs. Why? Fossils Strata Radiometric Dating Half Life C-14 U KEY EVENTS IN LIFE S HISTORY INCLUDE THE ORIGINS OF SINGLE-CELLED AND MULTICELLED ORGANISMS AND THE COLONIZATION OF LAND This time scale presents a record of changes in the geologic structure of the Earth over time. It provides a listing of the fossil and microfossil evidence of various life forms that existed throughout the changing time on our home planet. The revised Geologic Time Scale is divided into three eons: Phanerozoic Eon Cenozoic Era Neogene Period Paleogene Period Mesozoic Era Cretaceous Jurassic Triassic Paleozoic Era Permian Period 10

3 Carboniferous Period Devonian Period Silurian Period Ordovician Period Cambrian Proterozoic Eon Precambrian Neoproterozoic Edicaran Period 1 Billion 542 MYA Cryogenian Period MYA Tonian Period MYA Archaean Eon 3.6 BYA MYA (Archeozoic) Hadean Eon Earth s origins BYA The first autotrophs evolved from heterotrophs and were chemotrophs (green sulfur and purple sulfur bacteria). Cyanobacteria were the first bacterial forms to split water to get H + for food production (photosynthesis). Evolution of populations of photosynthetic autotrophs changed the planet s atmosphere over time. The ozone layer formed and provided UV light protection. At the end of the Paleozoic era, 90% of all species disappeared. When the Cretaceous period ended, (65 million years ago: the time of the great dying ) the big reptiles had vanished from the planet. Stromatolites Ediacara Endosymbiont Theory Eukaryotic cells descended from prokaryotic ones. A possible mechanism is suggested by Lynn Margulis, and is known as the endosymbionic theory (a/k/a endosymbiont theory). This theory states that there was an incorporation of prokaryote forms into existing organic masses, which provided survival advantage(s) for the prokaryotes. Evidence includes the fact that chloroplasts and mitochondria have their own primitive prokaryotic DNA. Examples of mutualistic relationships exist in nature and include termites (and roaches), which have flagellated protozoans that live in their gut. 11

4 The flagellate is Mixotricha paradoxa, a member of the Trichonympha. The protozoans have spirochaete bacteria mutualistically living on their surface. This complex association allows termites to digest cellulose THE RISE AND FALL OF DOMINANT GROUPS REFLECT CONTINENTAL DRIFT, MASS EXTINCTIONS, AND ADAPTIVE RADIATIONS We think that humans are the be-all and end-all of life forms, but we are not. Others in the Earth s past have been more successful and for longer periods of time than humans will ever be! Someday we will be gone like the dinosaurs. Why? Continental Drift Alfred Wegener Pangaea Laurasia Gondwana Tectonic Plates Sea-floor Spreading Alvarez Hypothesis Iridium Chicxulub Crater Big Five Mass Extinctions Time of Great Dying Index Fossils Punctuated Equilibrium Adaptive Radiation 25.5 MAJOR CHANGES IN BODY FORM CAN RESULT FROM CHANGES IN THE SEQUENCES AND REGULATION OF DEVELOPMENTAL GENES We study geological records, fossils, homologies, DNA comparisons, adaptive radiation and many more large-scale events to explain change over time. Intrinsic biological mechanisms (natural cellular events within cells and tissues) can help explain evolutionary changes. 12

5 Heterochrony Paedomorphsis Homeotic Genes Hox Genes Ubx Scr 25.6 EVOLUTION IS NOT GOAL ORIENTED New forms of organisms arise overtime through slight modifications of existing forms (Jacob of Jacob-Manod). Modifications can occur to developmental genes and/or to genes that govern structures. There is no drive towards a particular goal. Changes just occur. The results either work out or they don t. 13