Origion And History Of Life

CHAPTER 22 ORIGIN AND HISTORY OF LIFE

Prepared by

Brenda Leady, University of Toledo

1 reprod Copyright (c) The McGraw-Hill Companies, Inc. Permission required for

The universe began with the Big Bang about 13.7 bya  Our solar system began about 4.6 bya  The Earth is 4.55 billion years old  4 bya the Earth cooled enough for outer layers to solidify and oceans to form  4-3.5 bya life emerged 

2

3

Origin in 4 overlapping stages 1. 2.

3. 4.

Nucleotides and amino acids produced prior to the existence of cells Nucleotides and amino acids became polymerized to form DNA, RNA and proteins Polymers became enclosed in membranes Polymers enclosed in membranes evolved cellular properties

4

Stage 1: Origin of organic molecules Conditions on primitive Earth may have been more conducive to spontaneous formation of organic molecules  Prebiotic or abiotic synthesis 

 Formed



prebiotic soup

Several hypotheses on where and how organic molecules originated 5



Reducing atmosphere hypothesis  Based

on geological data  Experiments simulated conditions of primitive Earth postulated in 1950s  Formed precursors, amino acids, sugars and nitrogenous bases  First attempt to apply scientific experiments to understand origin of life  Since 1950s, ideas about early Earth atmosphere changed 

Similar results 6

7



Extraterrestrial hypothesis  Meteorites 

brought organic carbon to Earth

Includes amino acids and nucleic acid bases

 Opponents

argue that most of this would be destroyed in the intense heating and collision



Deep-sea vent hypothesis  Biologically

important molecules may have been formed in the temperature gradient between extremely hot vent water and cold ocean water  Supported by experiments  Complex biological communities found here that derive energy from chemicals in the vent (not the sun) 8

9

Stage 2: Organic polymers Experimentally, prebiotic synthesis of polymers not possible in aqueous solutions  Experiments have shown formation of nucleic acid polymers and polypeptides on clay surface 

10

Stage 3: Formation of boundaries 



Protobiont/ prebiont describes first nonliving structures that evolved into living cells 4 characteristics 1. 2. 3. 4.

Boundary separated external environment from internal contents Polymers inside the protobiont contained information Polymers inside the protobiont had enzymatic function Protobionts capable of self-replication

11

Living cells may have evolved from 

Coacervates  Droplets

that form spontaneously from the association of charged polymers  Enzymes trapped inside can perform primitive metabolic functions 

Microspheres  Small

water-filled vesicles surrounded by a macromolecular boundary



Liposomes  Vesicles

surrounded by a lipid layer  Clay can catalyze formation of liposomes that grow and divide  Can enclose RNA 12

13

Stage 4: RNA world  

Majority of scientists favor RNA as the first macromolecule of protobionts 3 key RNA functions 1. 2. 3.



Ability to store information Capacity for replication Enzymatic function – ribozymes

DNA and proteins do not have all 3 functions 14

Chemical selection 



Chemical within a mixture of different chemicals has special properties or advantages that cause it to increase in number compared to other chemicals in the mixture Hypothetical scenario with 2 steps 1.

One of the RNA molecules mutates and has enzymatic ability to attach nucleotides together 

2.

Advantage of faster replication

Second mutation produces enzymatic ability to synthesize nucleotides 

No reliance on prebiotic synthesis

15

16

Bartel and Szostak Demonstrated Chemical Selection in the Laboratory  





Began with synthesis of 1015 RNA molecules (long) Each RNA contained 2 regions – constant region the same in all the molecules and a variable region Also made short RNAs that were complementary to a portion of the long RNA and had a tag sequence to bind to beads If the long RNAs mutated and obtained enzymatic activity, the long RNA would be held to the short RNA bound to the beads

 

 



Long RNAs that had this ability formed pool #1 More long RNAs were made that were variations on Pool #1 Repeated several times Pool #10 showed enzymatic ability 3 million times higher that the original random pool Results showed that chemical selection improves the functional characteristics of a group of RNA molecules over time by increasing the proportions of those molecules with enhanced function

Advantages of DNA/RNA/protein world 

Information storage  DNA

would have relieved RNA of informational role and allowed RNA to do other functions  DNA is less likely to suffer mutations 

Metabolism and other cellular functions  Proteins

have a greater catalytic potential and efficiency  Proteins can perform other tasks – cytoskeleton, transport, etc. 20

History of life on Earth 

Geological time scale  Origin



4.55 bya to present

Precambrian- first 3 eons

21

22



Changes in living organisms the result of  Genetic

changes  Environmental changes Can allow for new types of organisms  Responsible for many extinctions 

23

Major environmental changes Climate/temperature  Atmosphere  Land masses  Flood  Glaciation  Volcanic eruptions  Meteoric impacts 

24

25

Mass extinctions 5 large mass extinctions  Near end of Ordovician, Devonian, Permian, Triassic, and Cretaceous periods  Geologic time periods are often based on these events 

26

Fossils Recognizable remains of past life on Earth  Paleontologists study fossils  Many rocks with fossils are sedimentary 

 Sediments

pile up and become rock  Organisms buried quickly and hard parts replaced by minerals 

Older rock is deeper and older organisms are deeper in the rock bed 27

28

Radioisotope dating Fossils can be dated using elemental isotopes in accompanying rock  Half-life – length of time required for exactly one-half of original isotope to decay  Measure amount of a given isotope as well as the amount of isotope produced when the isotope decays  Usually igneous rock dated  Expect fossil record to underestimate actual date species came into existence 

29

30

31

Prokaryotic cells arose during Archaeon Eon   

Archaeon Eon when diverse microbial life flourished in primordial oceans First known fossils 3.5 bya First cells prokaryotic  Bacteria

   

and Archaea are similar but different

All life forms prokaryotic during Archaeon Eon Hardly any free oxygen so organism were anaerobic First cells were heterotrophs Autotrophs evolved as supply of organic molecules dwindled

32

Stromatolites Autotrophic cyanobacteria were preserved when heterotrophic ancestors were not  Form stromatolites- layered structure of calcium carbonate  Cyanobacteria produce oxygen as a waste product of photosynthesis  Spelled doom for many prokaryotic groups that were anaerobic  Allowed the evolution of aerobic species 

33

34

The Origin of Eukaryotic Cells During the Proterozoic Eon Involved a Union Between Bacterial and Archaeal Cells    

Origin of first eukaryotic cell matter of debate In modern eukaryotes, DNA found in nucleus, mitochondria and chloroplasts Examine properties of this DNA and modern prokaryotes Nuclear genome – both bacteria and archaea contributed substantially  Symbiotic

relationship – 2 species live in direct contact  Endosymbitoic – one organism lived inside another 

Data supports this origin

Proterzoic Eon  

Multicellular eukaryotes arise 1.5 bya 2 possible origins  Individuals

form a colony  Single cell divides and stays stuck together   

Volvocine green algae display variations in the degree of multicellularity Multicellular animals emerge toward the end of the eon First animals invertebrates  Bilateral

symmetry facilitates locomotion 37

38

39

Phanerzoic Eon Proliferation of multicellular eukaryotic life extensive during Phanerzoic Eon (543 mya to today)  Paleozoic Era  Mesozoic Era  Cenozoic Era 

40

Phanerzoic Eon, Paleozoic Era 543-248 mya  Cambrian period  Ordovician period  Silurian period  Devonian period  Carboniferous period  Permian period 

41

Phanerzoic Eon, Paleozoic Era, Cambrian Period   

543-490 mya Warm and wet with no ice at poles Cambrian explosion – abrupt increase in diversity of animal species  Cause

unknown – shell evolution, atmospheric oxygen?

  

All existing major types of marine invertebrates plus many other that no longer exist Although new species have arisen since, no major reorganizations of body plans First vertebrates 520 mya 42

43

Phanerzoic Eon, Paleozoic Era, Ordovician Period      

490-443 mya Warm temperatures and atmosphere very moist Diverse group of marine invertebrates including trilobites and brachiopods Primitive land plants and arthropods first invade land Toward end, abrupt climate change (large glaciers) resulting in mass extinction Over 60% of existing marine invertebrates became extinct 44

45

Phanerzoic Eon, Paleozoic Era, Silurian Period        

443-417 mya Relatively stable climate Glaciers largely melted No new major invertebrates Significant new vertebrates and plants Many new fish Coral reefs appeared Large colonization by terrestrial plants and animals  Had

 

to evolve adaptations to drying out

Spiders and centipedes Earliest vascular plants

46

Phanerzoic Eon, Paleozoic Era, Devonian Period  

      

417-354 mya Generally dry across north but southern hemisphere mostly covered by cool, temperate oceans Major increase in number of terrestrial species Ferns, horsetails and seed plants (gymnosperms) emerge Insects emerge Tetrapods – amphibians emerge Invertebrates flourish in the oceans Age of Fishes Near end, prolonged series of extinctions eliminate many marine species

47

Phanerzoic Eon, Paleozoic Era, Carboniferous Period

354-290 mya  Rich coal deposits formed  Cooler, land covered by forested swamps  Plants and animals further diversified 

 Very

large plants and trees prevalent  First flying insects  Amphibians prevalent  Amniotic egg emerges - reptiles 48

49

Phanerzoic Eon, Paleozoic Era, Permian Period       

290-248 mya Continental drift formed supercontinent Pangaea Interior regions dry with seasonal fluctuations Forest shift to gymnosperms Amphibians prevalent but reptile became dominant First mammal-like reptiles appeared At the end, largest known mass extinction event  90-95%

of all marine species and large proportion of terrestrial species eliminated  Glaciations or volcanic eruptions blamed

50

Phanerzoic Eon, Mesozoic Era Permian extinction marks boundary between Paleozoic and Mesozoic eras  Age of Dinosaurs  Consistently hot climate, dry terrestrial environments, little if any ice at poles 

51

Phanerzoic Eon, Mesozoic Era, Triassic Period

248-206 mya  Reptiles plentiful  First dinosaurs  First true mammals  Gymnosperms dominant land plant  Volcanic eruptions led to global warming and mass extinctions near the end 

52

Phanerzoic Eon, Mesozoic Era, Jurassic Period

206-144 mya  Gymnosperms continued to be dominant  Dinosaurs dominant land animal  Some attained enormous size  First known bird  Mammals present but not prevalent 

53

54

Phanerzoic Eon, Mesozoic Era, Cretaceous Period      

144-65 mya Dinosaurs still dominant on land Earliest flowering plants, angiosperms Another mass extinction at the end of the period Dinosaurs and many other species died out Large meteorite/asteroid or volcanic eruptions blamed

55

Phanerzoic Eon, Cenozoic Era Spans most recent 65 million years  Tropical conditions replaced by a colder, drier climate  Amazing diversification of birds, fish, insects, and flowering plants 

56

Phanerzoic Eon, Cenozoic Era, Tertiary Period        

65-1.8 mya Mammals that survived expanded rapidly Birds and terrestrial insects diversified Angiosperms become the dominant land plant Fish diversified Sharks become abundant Whales appeared Hominids appeared about 7 mya 57

Phanerzoic Eon, Cenozoic Era, Quaternary Period

1.8 mya to present  Periodic ice ages cover much of Europe and North America  Widespread extinction of many species  Certain hominids become more humanlike  Homo sapiens appears 130,000 years ago 

58