4 1. Life on Earth originated between 3.5 and 4.0 billion years ago organisms were microscopic and mostly unicellular.2. Prokaryotes dominated evolutionary history from 3.5 to 2.0 billion years agoprokaryotes diverged into two main evolutionary branches, the bacteria and the archaea.
5 1. stromatolites (fossilized layered microbial mats) Two rich sources for early prokaryote fossils are:1. stromatolites (fossilized layered microbial mats)2. sediments from ancient hydrothermal vent habitats.stromatolitesStromatolite = 墊藻岩 ( 由鈣質藻類形成的薄片狀石灰岩 )Fig. 26.4
7 3. Oxygen began accumulating in the atmosphere about 2 3. Oxygen began accumulating in the atmosphere about 2.7 billion years agoearly versions of photosynthesis did not split water and liberate oxygen.Cyanobacteria, photosynthetic organisms that split water and produce O2 as a byproductWater were saturated with O2 extra O2 reacted with dissolved iron to form the precipitate iron oxide. (banded iron with red color) [Fig 26.5]all iron preciptate oxygen began accumulating in the atmosphere (10% of current values)
9 4. Eukaryotic life began by 2.1 billion years ago Eukaryotic cells are generally larger and more complex than prokaryotic cells.In part, this is due to “endosymbiotic prokaryotes” that evolved into mitochondria and chloroplasts.The evolution of chloroplasts and mitochondrion, turned the accumulating O2 to metabolic advantage through cellular respiration.
10 5. Multicellular eukaryotes evolved by 1.2 billion years ago A great range of eukaryotic unicellular forms evolved into the diversity of present-day “protists.”單細胞生物 protistFossilzed algawith more than2 types of cellsFig. 26.6
11 snowball Earth hypothesis ice age (750 to 570 million years ago) may be responsible for the limited diversity and distribution of multicellular eukaryotes until the very late Precambrian. The first major diversification at the time of thawing of snowball Earth.Ice age 冰河時期
12 6. Animal diversity exploded during the early Cambrian period = Cambrian radiation(explosion) of animalextent from their first fossilSee detail in chapter 32-34Fig. 26.8
13 7. Plants, fungi, and animals colonized the land about 500 million years ago Plants colonized land in association with fungi. symbiotic associationherbivorous (plant-eating) animals and their predators.The most widespread and diverse terrestrial animals are certain arthropods and certain vertebrates.Most orders of modern mammals, including primates, appeared million years ago.Humans diverged from other primates only 5 million years ago
14 Introduction Hypothesis: CHAPTER 26 EARLY EARTH AND THE ORIGIN OF LIFESection B: The Origin of LifeIntroductionHypothesis:4.0 billion years ago the Earth’s crust began to solidify3.5 billion years ago stromatolites appear the first organisms
15 1. The first cells may have originated by chemical evolution on a young Earth: an overview Most scientists favor the hypothesis that life on Earth developed from nonliving materials, an idea called spontaneous generation.
16 In 1862, Louis Pasteur conducted broth experiments that rejected the idea of spontaneous generation. Although there is no evidence that spontaneous generation occurs today, conditions on the early Earth were very different.Fig. 26.9
17 the principle of biogenesis All life today arises only by the reproduction of preexisting life.hypothesis is that chemical and physical processes in Earth’s primordial environment eventually produced simple cells.four stages that can be tested in the laboratory:(1) the abiotic synthesis of small organic molecules;(2) joining these small molecules into polymers:(3) origin of self-replicating molecules;(4) packaging of these molecules into “protobionts.”
18 2. Abiotic synthesis of organic molecules is a testable hypothesis In the 1920’s, A.I. Oparin and J.B.S. Haldane independently postulatedthat conditions on the early Earth favored the synthesis of organic compounds from inorganic precursors.The reducing environment in the early atmosphere promoted the joining of simple molecules to form more complex ones.
19 In 1953, Stanley Miller and Harold Urey tested the Oparin-Haldane hypothesis The atmosphere in the Miller-Urey model is more strongly reducing environment than is currently believed.amino acids & organic molecules.Fig
20 3. Laboratory simulations of early-Earth conditions have produced organic polymers The abiotic origin hypothesis predicts that monomers should link to form polymers without enzymes and other cellular equipment.
21 4. RNA may have been the first genetic material Today, cells store their genetic information as DNA transcribe into RNA translate into enzymes and other proteins.Many researchers have proposed that the first hereditary material was RNA, not DNA.Because RNA can also function as an enzymes, it helps resolve the paradox of which came first, genes or enzymes.
22 Short polymers of ribonucleotides can be synthesized abiotically in the laboratory. base-pairing rules up to 10 bpIf zinc is added, may reach 40 bp with less than 1% error.Fig
23 In the 1980’s Thomas Cech discovered that RNA molecules are important catalysts in modern cells. Ribozymes1. RNA catalysts that remove introns from RNA.2. help catalyze synthesis of new RNA polymers. In the pre-biotic world, RNA molecules may have been fully capable of ribozyme- catalyzed replication.
24 RNA sequences can evolve in abiotic conditions. RNA molecules have both a genotype (nucleotide sequence) and a phenotype (three dimensional shape) that interacts with surrounding molecules.some RNA sequences are more stable, replicate faster and with fewer errors.RNA-directed protein synthesis is one function of rRNA today in ribosomes.
25 5. Protobionts can form by self-assembly Living cells may have been preceded by protobionts, aggregates of abiotically produced molecules.Protobionts do not reproduce precisely, but they associate with life, metabolism, and excitability.Proto =最初, 原始; bionic =仿生學的; protobiont =原生物 ( 原始的有機體 )
26 In the laboratory, lipid droplets of abiotically produced liposomes form a molecular bilayer, like bio-membrane. [growth]SimplereproductionFig a
27 absorb Simple metabolism release Fig. 26.12b If enzymes are included in the solution from droplets self-assemble, some protobionts can carry out simple metabolic pathways.Fig b
28 6. Natural section could refine protobionts containing hereditary information Fig
29 Evolution refined primitive metabolism and inheritance. The most successful protobionts would grow and split, distributing copies of their genes to offspring.Evolution refined primitive metabolism and inheritance.One refinement was the replacement of RNA as the repository of genetic information by DNA, a more stable molecule.
30 7. Debates about the origin of life abounds It is proposed that ancestors of modern prokaryotes thrived in very hot conditions and may have lived on inorganic sulfur compounds that are common in deep- sea vent environments.Hypothesis: life is not restricted to Earth.The presence of ice on Europa, a moon of JupiterMars is cold, dry, and lifeless today.木星 Jupiter;Europa = [希神】 歐羅巴 ( Phoenicia 國王之女; Zeus 所愛的女人,宙斯變成白公牛將她拐走 )=木衛二 ( Galilean satellites ) ( 木星的第二衛星 )
32 1. The five-kingdom system reflected increased knowledge of life’s diversity In the early days of biology, all organisms were classified as either plants or animals. [Linnaeus]Single-celled eukaryotic organisms such as algae and Paramecium plant kingdoms [photosynthetic]Fungi and prokaryotes plants[fungi are sedentary and prokaryotes have cell walls.]Paramecium = 草履蟲
33 In 1969, R.H WhittakerThe five-kingdom system prevailed in biology for over 20Yr.autotrophicdecomposerDifferent NutritionMonera = ; Protista = 原生生物界Most protists are unicellular.However, some multicellular organisms were included in Protista because of their relationships to specific unicellular protists.Fig
34 2. Arranging the diversity of life into the highest taxa is a work in progress During the last 30Yr, cladistic analysis have been identifying problems with the five- kingdom system. two distinct lineages of prokaryotes.three-domain system:Bacteria, Archaea, and Eukarya, as superkingdoms.cladistic 依據遺傳因素與血統關係的
35 FigMany microbiologists have divided the two prokaryotic domains into multiple kingdoms (based on cladistic analysis of molecular data.)Cladistic =依據遺傳因素與血統關係的; phylogenetic = 系統發育的Keep in mind that phylogenetic trees and taxonomic groupings are hypotheses that fit the best available data.