1. CHAPTER 26 EARLY EARTH AND THE ORIGIN OF LIFE
Section A: Introduction to the History of Life
張學偉 助理教授 生物系
Cambrian =寒武紀的

2. Introduction phylogenetic tree chronology episodes Fig. 26.1
Cenozoic =Cainozoic 新生代的; Mesozoic 中生代的; Paleozoic 古生代的
phylogenetic
tree
Fig. 26.1

3. The clock ticks down from the origin of Earth to the present.
Fig. 26.2
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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 ago
prokaryotes 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.
stromatolites
Stromatolite = 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 ago
early versions of photosynthesis did not split water and liberate oxygen.
Cyanobacteria, photosynthetic organisms that split water and produce O2 as a byproduct
Water 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)

8. terrestrial rocks with iron began oxidizing.
This “corrosive” O2 had an enormous impact on life, dooming many prokaryote groups.
terrestrial rocks with iron began oxidizing.
Some species survived in habitats that remained anaerobic.
Other species evolved mechanisms to use O2 in cellular respiration (aerobic).
Corrosive 侵蝕性的
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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 protist
Fossilzed alga
with more than
2 types of cells
Fig. 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 animal
extent from their first fossil
See detail in chapter 32-34
Fig. 26.8

13. 7. Plants, fungi, and animals colonized the land about 500 million years ago
Plants colonized land in association with fungi.  symbiotic association
herbivorous (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 LIFE
Section B: The Origin of Life
Introduction
Hypothesis:
4.0 billion years ago the Earth’s crust began to solidify
3.5 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 postulated
that 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 bp
If 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.
Ribozymes
1. 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]
Simple
reproduction
Fig 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 Jupiter
Mars 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 )

31. CHAPTER 26 EARLY EARTH AND THE ORIGIN OF LIFE
Section C: The Major Lineages of Life
1. The five kingdom system reflected increased knowledge of life’s diversity
2. Arranging the diversity of life into the highest taxa is a work in progress
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

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 Whittaker
The five-kingdom system prevailed in biology for over 20Yr.
autotrophic
decomposer
Different Nutrition
Monera = ; 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. Fig
Many 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.