1. Chapter 19 Life’s Origin and Early Evolution

2. 19.1 Looking for Life
Astrobiology is the study of life’s origins and distribution – astrobiologists study Earth’s extreme habitats to determine the range of conditions living things can tolerate
Life on Earth is protected by the ozone layer, which serves as a natural sunscreen, preventing most UV radiation from reaching the planet’s surface
Life can adapt to nearly any environment with sources of carbon and energy – including extreme temperatures, pH, salinity, or pressure

3. Lessons from Chile’s Atacama Desert
Figure 19.1 The Mars-like landscape of Chile’s Atacama Desert. Scientist Jay Quade, visible in the distance at the right, was a member of a team that found bacteria living beneath this arid desert soil.

4. 19.2 The Early Earth
Knowledge of modern chemistry and physics are the basis for scientific hypotheses about early events in Earth’s history

5. Origin of the Universe and Our Solar System
Big bang theory
The universe began in an instant, 13-5 billion years ago
All existing matter and energy suddenly appeared and exploded outward from a single point
The universe is still expanding
Earth formed from dust and debris orbiting the sun, about 4.6 billion years ago

6. Formation of the Earth
Figure 19.2 Artist’s depiction of our sun surrounded by a cloud of dust, debris, and gases. Earth and other planets formed from the material in this cloud.

7. Conditions on the Early Earth
Earth’s early atmosphere came from gas released by volcanoes, and was low in oxygen
Rain washed minerals and salts out of rocks to form early seas

8. ANIMATION: Origin of organelles
To play movie you must be in Slide Show Mode
PC Users: Please wait for content to load, then click to play
Mac Users: CLICK HERE

9. Early Earth
Figure 19.3 An artist’s depiction of early Earth.

10. Take-Home Message: What were conditions like on the early Earth?
Earth’s early atmosphere had little or no oxygen
Meteorites pummeled the planet’s surface, and volcanic activity was more common than it is today

11. 19.3 Formation of Organic Monomers
All living things are made from the same organic subunits: amino acids, fatty acids, nucleotides, and simple sugars
Small organic molecules that serve as building blocks of life can be formed by nonliving mechanisms

12. Possible Sources of Life’s First Building Blocks
Stanley Miller showed that amino acids form in conditions that simulate lightning in the atmosphere of early Earth
Wächtershäuser and Huber synthesized amino acids in a simulated hydrothermal vent environment
Amino acids, sugars, and nucleotide bases may have formed in interstellar clouds and been carried to Earth on meteorites

13. water containing organic compounds
electrodes
to vacuum pump
spark discharge
CH4 NH3 H2O H2
gases
water out
condenser
water in
water droplets
water containing organic compounds
boiling water
liquid water in trap
Figure 19-4 p311 13

14. A Hydrothermal Vent on the Seafloor
Figure 19.5 A hydrothermal vent on the seafloor. Mineral-rich water heated by geothermal energy streams out, into cold ocean water. As the water cools, dissolved minerals come out of solution and form a chimney-like structure around the vent.

15. Take-Home Message: What was the source of organic molecules to build the first life?
Small organic molecules that serve as the building blocks for living things can be formed by nonliving mechanisms.
For example, amino acids form in reaction chambers that simulate conditions on the early Earth, and are present in some meteorites

16. ANIMATED FIGURE: Miller's reaction chamber experiment
To play movie you must be in Slide Show Mode
PC Users: Please wait for content to load, then click to play
Mac Users: CLICK HERE

17. 19.4 From Polymers to Protocells
We will never know for sure how the first cells came to be, but we can investigate the possible steps on the road to life

18. Properties of Cells
All living cells carry out metabolic reactions, are enclosed within a plasma membrane, and can replicate themselves
Cells have a genome of DNA that enzymes transcribe into RNA, and ribosomes that translate RNA into proteins
Studies support the hypothesis that cells arose from a stepwise process that began with inorganic materials

19. …self-assemble on Earth and in space
inorganic molecules
…self-assemble on Earth and in space
organic monomers
…self-assemble in aquatic environments on Earth
organic polymers
…interact in early metabolism
…self-assemble as vesicles
…become the first genome
protocells in an RNA world
…are subject to selection that favors a DNA genome
DNA-based cells
Figure 19-6 p312 19

20. Origin of Metabolism
Before cells, nonbiological process that concentrate organic subunits might increase the chance of polymer formation
Concentration of molecules on clay particles in tidal flats may have caused organic subunits to bond as polymers
The iron–sulfur world hypothesis holds that the first metabolic reactions began on the surface of rocks around hydrothermal vents

21. Origin of the Genome
An RNA-based system of inheritance may have preceded DNA-based systems
RNA world hypothesis
RNA may have stored genetic information and functioned like an enzyme in protein synthesis
RNAs that function as enzymes (ribozymes) are common in living cells today

22. Origin of the Plasma Membrane
The cell’s plasma membrane allows organic molecules to concentrate and undergo reactions
Membranous sacs (protocells) containing interacting organic molecules may have formed prior to the earliest life forms
In experiments, small organic molecules can react with minerals and seawater to form vesicles with a bilayer membrane

23. Laboratory-Produced Protocells
A Illustration of a laboratory-produced
protocell with a bilayer membrane of fatty
acids and strands of RNA inside.
B Laboratory-formed protocell consisting
of RNA-coated clay (red) surrounded by
fatty acids and alcohols.

24. Testing a Hypothesis
C Field-testing a hypothesis about protocell formation.
David Deamer pours a mix of small organic molecules
and phosphates into a hot acidic pool in Russia.

25. Take-Home Message: What do experiments reveal about steps that led to the first cells?
All living cells carry out metabolic reactions, are enclosed within a plasma membrane, and can replicate themselves
Metabolic reactions may have begun when molecules became concentrated on clay particles or in tiny rock chambers near hydrothermal vents
RNA can serve as an enzyme, as well as a genome. An RNA world may have preceded evolution of DNA-based genomes
Vesicle-like structures with outer membranes form spontaneously when certain organic molecules are mixed with water

26. 19.5 Life’s Early Evolution
Fossils and molecular comparisons among modern organisms inform us about the early history of life

27. Origin of Bacteria and Archaea
Life that arose 3-4 billion years ago was probably anaerobic and used dissolved carbon dioxide as a carbon source
Early fossil cells are similar in size and structure to modern archaea and bacteria
The first photosynthetic cells were bacteria that used the cyclic pathway (does not produce O2)

28. Fossil Prokaryotic Cells
A Possible cells from 3.5 billion years ago.
B Two types of cyanobacteria from 850 million years ago.

29. The Proterozoic Era
The oxygen-producing, non-cyclic pathway of photosynthesis first evolved in cyanobacteria
In the Proterozoic era Layers of photosynthetic bacteria formed large dome-shaped, layered called stromatolites
Oxygen accumulation in air and seas halted spontaneous formation of molecules of life, formed a protective ozone layer, and spurred evolution of organisms using aerobic respiration

30. Stromatolites
C Artist’s depiction of stromatolites. The surface of each stromatolite consists of a
mat of living photosynthetic bacteria. Beneath it are layers of earlier generations of
bacteria that trapped sediment and precipitated minerals. The inset photo shows
the layered structure of a fossil stromatolite.

31. The Rise of Eukaryotes
The earliest evidence of eukaryotes is lipids in 2.7-billion-year-old rocks – the lipids are biomarkers for eukaryotes
A red alga that lived 1.2 billion years ago is the oldest species known to reproduce sexually, a trait unique to eukaryotes
Multicellularity and cellular differentiation allowed evolution of larger bodies with specialized parts
Spongelike animals evolved about 870 million year ago; animals with more complex bodies existed about 570 mya

32. Fossils of Some Early Eukaryotes
A Grypania spiralis; 2.1 billion years ago
B Tawuia; 1.6 billion years ago
C Bangiomorpha pubescens; 1.2 billion years ago

33. Take-Home Message: What was early life like and how did it change Earth?
Life arose by 3–4 billion years ago; it was probably anaerobic and did not have a nucleus
An early divergence separated ancestors of modern bacteria from the lineage that lead to archaea and eukaryotic cells
The first photosynthetic cells were bacteria that used the cyclic pathway; later, the oxygen-producing, noncyclic pathway evolved in cyanobacteria
Oxygen accumulation in air and seas halted spontaneous formation of the molecules of life, formed a protective ozone layer, and favored organisms that carried out the highly efficient pathway of aerobic respiration

34. 19.6 How Did Eukaryotic Traits Evolve?
Eukaryotic cells have a composite ancestry, with different components derived from different lineages
Archaea-like nuclear genes govern genetic processes (DNA replication, transcription, translation)
Bacteria-like nuclear genes govern metabolism and membrane formation

35. Origins of Internal Membranes
In eukaryotes, DNA resides in a nucleus bordered by a nuclear envelope – a double membrane with pores that control the flow of material into and out of the nucleus
A few modern bacteria also have internal membrane-enclosed compartments
The nucleus and endomembrane system probably evolved from infoldings of plasma membrane

36. infolding of plasma membraneER
Figure Evolution of internal membranes.
A Infoldings of the plasma membrane could have evolved into
the eukaryotic nuclear envelope and endomembrane system.
nuclear envelope
19-10a p1910 36

37. Bacteria with Internal Membranes
B Bacterium (Nitrosococcus oceani)
with highly folded internal membranes
visible across its midline.
C Bacterium (Gemmata obscuriglobus)
that has DNA enclosed by a two-layer
membrane (indicated by the arrow).

38. Evolution of Mitochondria and Chloroplasts
The endosymbiont hypothesis holds that mitochondria and chloroplasts descended from bacteria that were prey or parasites of early eukaryotic cells
Mitochondria are genetically similar to aerobic bacteria called rickettsias; chloroplasts are similar to photosynthetic bacteria called cyanobacteria

39. Rickettsia prowazekii

40. Evidence of Endosymbiosis
Endosymbiosis can occur when a bacterium infects a eukaryotic cell
Eventually, host and symbiont become incapable of living independently
Example: The photosynthetic organelles of glaucophytes are dependent on their host – they can’t survive on their own

41. photosynthetic organelle that resembles a cyanobacterium
Figure Cyanophora paradoxa, a glaucophyte protist with large photosynthetic organelles that make the bacterial protein peptidoglycan.
Figure 19-12a p317

42. photosynthetic organelle that resembles a cyanobacterium
Figure Cyanophora paradoxa, a glaucophyte protist with large photosynthetic organelles that make the bacterial protein peptidoglycan.
Figure 19-12b p317

43. Take-Home Message: How might eukaryotic organelles have evolved?
A nucleus and other organelles are defining features of eukaryotic cells
The nucleus and ER may have arisen through modification of infoldings of the plasma membrane
Mitochondria and chloroplasts most likely descended from bacteria

44. 19.7 Time Line for Life’s Origin and Evolution

45. Table 19-1 p320

46. ANIMATION: Evolutionary tree of life
To play movie you must be in Slide Show Mode
PC Users: Please wait for content to load, then click to play
Mac Users: CLICK HERE

47. ANIMATED FIGURE: Milestones in the history of life
To play movie you must be in Slide Show Mode
PC Users: Please wait for content to load, then click to play
Mac Users: CLICK HERE