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1. Chapter 26:
Early Earth and the Origin of LifeEarly Earth and the Origin of Life

2. Some
major
episodes in
the history
of life.

3. Clock
analogy for
some key
events in
evolutionary
history

4. 1. The earth was formed ~4.5 billion years ago
2. It took ~500 million years for the crust to solidify.
3. The oldest fossils of microorganisms
• 3.5 billion years old,
• embedded in rocks in western Australia
3a. Prokaryotes dominated from 3.5 to 2 billion years ago.
- During this time, the first divergence occurred:
Bacteria and Archae

5. Early and modern prokaryotes

6. Fossilized evidence of bacteria
 Stromatolites are fossilized bacterial mats. Many fossils
of prokaryotes are found in layers that make up the
prokaryotic mats.

7. Bacterial mats and
stromatolites

12. 4. Oxygen began accumulating in the atmosphere about 2.7
billion years ago.
a. Cyanobacteria are photosynthetic prokaryotes that are
still present today  produced oxygen.

13. Banded iron formations are evidence of the age of oxygenic
photosynthesis – approximately 2 BYA in photo

14. 5. The oldest eukaryotic fossils are ~2 billion years old.
a. Symbiotic community of prokaryotes living within
larger prokaryotes.
 Mitochondria and chloroplasts
6. The oldest fossils of multicellular organisms are ~1.2
billion years old.

15. Endosymbiosis theory (Lynn Margulis, 1970’s)

17. Eukaryotic Origins
• A. Invagination of plasma membrane
• B. Endosymbiosis
– Symbiosis : An ecological relationship between
organisms of 2 different species that live
together in direct contact.
– How did this get started?
• prey or parasite

18. Evidence
• modern-day endosymbiotic relationships
– common among protists
• similarity between eubacteria & the
chloroplasts & mitochondria of eukaryotes
– size
– inner membrane systems, enzymes, electron transport
systems
– reproduction resembles binary fission
– circular DNA

21. Note the presence of
two types of cells
(photosynthetic and
hold fast) – evidence
of specialization of
cells functions, that
are important for
development of
multicellular organisms

22. 7. The oldest animal fossils are ~700 million years old.
a. Animal diversity exploded ~540 million years ago.

23. Fossilized animal embryos from Chinese sediments
570 million years ago.

24.
8. Plants, fungi, and animals began colonizing land ~500
million years ago.
a. First plants transformed the landscape…
b. Then animals were able to take advantage of new niches
 Mammals evolved 50 to 60 million years ago.

25. The
Cambrian
radiation
of animals

26. B. The origin of life
1. First cells may have originated by chemical evolution
involving 4 steps:
a. Abiotic (Non-biological) synthesis of small organic
molecules (monomers)  C + H = organic molecule
b. Monomers joined together to form polymers (proteins,
nucleic acids)
c. Origin of self-replicating molecules (inheritance of traits)
 proteins and polynucleic acids
d. Packaging of these organic molecules into protobionts. 
Aggregates of abiotically produced molecules that maintain
an internal chemical environment and exhibit some of the
properties associated with life (i.e. metabolism, excitability).

27. 2. Evidence that supports the four-stage hypothesis for the
origin of life
a. Oparin and Haldane in the 1920s  Abiotic synthesis of
organic molecules is testable in the laboratory
Hypothesis: Conditions on primitive earth favored chemical
reactions that synthesized organic compounds from inorganic
precursors. These conditions were different from what is now
present and include:
- Reducing environment (no oxygen, but instead H2O, CH4,
NH4, and H2) = lots of free electrons that could be used to
reduce carbon and produce organic molecules.
- Energy from lots of lightning, UV radiation (no O2 to block
UV rays from the sun) and volcanic activity (heat).

30. b. Miller and Urey in 1953
i. Tested the Oparin-Haldane hypothesis by creating
conditions in which there was an
- Atmosphere above warmed sea water that contained H2
O,
H2
, CH4
, and NH3
and
- Electrodes that simulated lightning.
- From this setup, they obtained organic compounds such as
amino acids that were collected in cooled water.

31. The Miller-
Urey
experiment

32. The experiment - organic molecules could be created out of
inorganic molecules.
So…….why don’t we see this happening in today’s world?
Any organic molecules that are now formed would be
used up by living organisms.
If microorganisms were created from these organic
molecules in the early earth’s water bodies, this would have
been an example of spontaneous creation!
For much of history, man believed that living organisms could
be created spontaneously from non-living material (e.g. flies
from dead meat, geese from barnacles, etc.)
This idea was refuted by Louis Pasteur in the 1860’s.

33. 3. RNA was probably the first hereditary material
a. Today, genetic information is usually stored as DNA, but
some organisms such as viruses use RNA to store info.

34. • Short polymers of ribonucleotides can be
synthesized abiotically in the laboratory.
– If these polymers are added to a solution of
ribonucleotide monomers, sequences up to 10 based
long are copied from the template according to the
base-pairing rules.
– If zinc is added, the copied sequences may reach 40
nucleotides with less than 1% error.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 26.11

35. • In the 1980’s Thomas Cech discovered that
RNA molecules are important catalysts in
modern cells.
• RNA catalysts, called ribozymes, remove
introns from RNA.
• Ribozymes also help catalyze the synthesis of
new RNA polymers.
• In the pre-biotic world, RNA molecules may
have been fully capable of ribozyme-catalyzed
replication.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

36. • Laboratory experiments have demonstrated
that 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.
• Under particular conditions, some RNA
sequences are more stable and replicate faster
and with fewer errors than other sequences.
– Occasional copying errors create mutations and
selection screens these mutations for the most
stable or best at self-replication.

37. • RNA-directed protein synthesis may have
begun as weak binding of specific amino acids
to bases along RNA molecules, which
functioned as simple templates holding a few
amino acids together long enough for them to
be linked.
– This is one function of rRNA today in ribosomes.
• If RNA synthesized a short polypeptide that
behaved as an enzyme helping RNA
replication, then early chemical dynamics
would include molecular cooperation as well
as competition.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

38. 4. The precursors of early life are known as Protobionts.
a. Protobionts form spontaneously in lab experiments from
mixtures of organic molecules.
b. They contain RNA that codes for metabolic proteins.
These protobionts absorb food and the proteins catalyze it
to make energy which can be used for growth and division
to daughter cells.
c. Natural selection would favor protobionts that grow and
replicate. When the organic molecules in the earth’s water
bodies were gone, the protobionts would “evolve” to either
obtain energy by photosynthesis or predation.
 It would only take the creation and evolution of one (1)
protobiont to give rise to the all the different organisms we
see today.

40. • Once primitive RNA genes
and their polypeptide products
were packaged within a
membrane, the protobionts
could have evolved as units.
• Molecular cooperation could
be refined because favorable
components
were concentrated
together, rather than
spread throughout the
surroundings.
6. Natural section could refine protobionts
containing hereditary information
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 26.13

41. This 4.5 billion-year-old rock, labeled meteorite ALH84001, is believed to have once been
a part of Mars and to contain fossil evidence that primitive life may have existed on Mars
more than 3.6 billion years ago. The rock is a portion of a meteorite that was dislodged
from Mars by a huge impact about 16 million years ago and that fell to Earth in Antarctica
13,000 years ago. The meteorite was found in Allan Hills ice field, Antarctica, by an
annual expedition of the National Science Foundation's Antarctic Meteorite Program in
1984. It is preserved at the Johnson Space Center's Meteorite Processing Laboratory in
Houston.

42. c. Louis Pasteur in the 1860s
i. Tested whether microorganisms emerge by spontaneous
generation or by reproduction of existing microorganisms.
- Microorganisms grew in open containers of sterilized broth.

45. C. Major lineages of life
1. At first, two kingdoms were recognized  Plants and
Animals.
2. In 1969, Robert Whittaker developed a five-kingdom
system  Plants, Fungi, Animals, Protists, and Prokaryotes
(Monera).

47. Whittaker’s
five-
kingdom
system

48. Our changing view of biological diversity