1. The Origin and Early History of Life
Chapter 4

2. Outline
Origin of Life Hypotheses
Chemical Evolution
Cell Origin Theories
Bubble Theories
Prokaryotic Cells
Archaebacteria
Bacteria
Eukaryotic Cells
Extraterrestrial Life

3. What do we know? ~ 1.5 Million species identified so far
Many more remain unidentified

4. Are we alone?
Yes No

5. Which one represents possible origin of life on earth?
Extraterrestrial aliens brought it
Came with meteors from other planets
Some superhuman powers created it
Chemicals from primordial soup combined to make life
None of the above

6. What have we learned so far?
Cell theory
All living organisms are made of cells, and all living cells come from other living cells.
Molecular basis of inheritance
DNA encodes genes which make-up and control living organisms.
Evolutionary change
Life-forms have evolved varying characteristics to adapt to varied environments.
Evolutionary conservation
Some characteristics of earlier organisms are preserved and passed on to future generations.

7. Where the first cell came from?
Or….Can life arise from non-life?
Can we test this scientifically?
Conditions on early earth
Formation of organic molecules
Chemical evolution
Primitive cell
Prokaryotes
Eukaryotes
Multicellular organisms

8. Conditions on Early Earth- Reducing Atmosphere
Life most likely emerged under high-temperature conditions.
Early atmosphere is often referred to as a reducing atmosphere.
exact conditions unknown
ample availability of hydrogen atoms
very little oxygen

9. Origin of Life - Location
Ocean’s edge
bubble hypotheses
Under frozen seas
problematic due to necessary conditions
Deep in Earth’s crust
byproduct of volcanic activity
Within clay
positively-charged clay
Deep-sea vents
conditions suitable for Archaea

10. Miller-Urey Experiment
Attempted to reproduce early reducing atmosphere and produce organic compounds from inorganic materials
hydrogen-rich
electrical discharges
Produced
amino acids
carbohydrates
lipids
nucleotides

11. Chemical Evolution
If life originally arose from non-life, how might this have happened?
Consider the following scenario
Synthesis and accumulation of small organic molecules
Joining of these monomers into polymers
Aggregation of these molecules into droplets to form localized microenvironments
Origin of heredity

12. Polymer Formation
Sidney Fox (University of Miami) demonstrated the abiotic polymerization of organic monomers
Polymers were formed when dilute solutions of organic molecules were dripped onto hot sand, clay, or rock
“Proteinoids”
Clay can serve to concentrate these molecules
Monomers bind to charged sites on clay particles
Metal ions in clay have catalytic function

13. Which came first? DNA RNA Protein Most Likely DNA  RNA  PROTEIN
(Genetic information) (Information and catalytic) (Catalytic and structural)

14. Abiotic RNA Replication
Remember RNA enzymes?

15. Lets make something with those molecules
Aggregations of abiotically produced molecules
Preceded living cells
Laboratory experiments have demonstrated their formation from organic compounds
Protobionts and liposomes

16. Origin of protobiots
Bubble theories (Oparin)

17. PROTO-CELLS
Chemical evolution ultimately led to the formation of proto-cells
Membrane-surrounded sacs containing genetic material and metabolically-active molecules
Such structures have been experimentally produced
From these proto-cells, cells ultimately arose

18. Microfossils have been found in rocks as old as 3.5 billion years old.
Earliest Cells
Microfossils have been found in rocks as old as 3.5 billion years old.
resemble prokaryotes
Stromatolites

19. EARLIEST LIFE The earliest cells were prokaryotic
Lack a membrane-bound nucleus
Early in the history of life, populations diverged into two major lineages
 bacteria
 archaea & eukaryotes

20. Archaebacteria
Extreme-condition prokaryotes
lack peptidoglycan in cell walls
methanogens
extreme halophiles
extreme thermophiles
thought to have split from Bacteria 2 bya.

21. Bacteria
Second major group of prokaryotes
strong cell walls
simpler gene structure
contains most modern prokaryotes
includes photosynthetic bacteria
cyanobacteria

22. EARLIEST LIFE
How do we know that domain Eukarya is more closely related to domain Archaea than to domain Bacteria?
Analysis of rRNAs and other highly conserved genes and proteins provide the strongest evidence

23. First Eukaryotic Cells
Eukaryotes probably arose about 1.5 bya.
Internal membrane-bound structures such as mitochondria and chloroplasts are thought to have evolved via endosymbiosis.
Energy-producing bacteria were engulfed by larger bacteria.
beneficial symbiotic relationship

24. First Eukaryotic Cells
Sexual reproduction
Eukaryotic cells can reproduce sexually, thus allowing for genetic recombination.
Genetic variation is the raw material necessary for evolution.
Multicellularity
arisen many times among eukaryotes
fosters specialization

25. Development of new branches on the TREE

26. TAXONOMY

27. Extraterrestrial Life
Universe has 1020 stars similar to our sun.
Conditions may be such that life has evolved on other worlds in addition to our own.
ancient bacteria on Mars.
largest moon of Jupiter, Europa, covered with ice.
liquid water may be underneath

28. The Domains and Kingdoms

29. What they have and what they don’t

30. What about this group?

31. Summary
Fundamental Properties of Life
Origin of Life Hypotheses
Chemical Evolution
Cell Origin Theories
Bubble Theories
Prokaryotic Cells
Archaebacteria
Bacteria
Eukaryotic Cells
Extraterrestrial Life