3. The big bang is how astronomers
explain the way the universe
began.
It is the idea that the universe
began as just a single point, then
expanded and stretched to grow
as large as it is right now—and it
is still stretching!
4. Prebiotic Earth
Conditions on the primitive Earth were
not the same as those present today
No spontaneous generation of life today
(Pasteur)…
because the necessary conditions no
longer exist.
5. Conditions on early Earth
Reducing atmosphere on the primitive Earth. No free
oxygen (O2)
Free hydrogen (H2) and saturated hydrides (CH4, NH3
and H2O)
Energy for chemical reactions between these gases
could come from electric discharge in storms or solar
energy (no ozone layer)
The Earth’s surface temperature probably hotter than
today.
6.
7. The formation of monomers
Miller and Urey
recreate these
conditions in vitro
The water is heated
and the mixture
circulates for many
days.
H2
NH3
CH4
H2O
H2O
Heat
Electric
discharge
Samples
8.
9. Results
After a week 15 amino acids in the
mixture
Other biologically important
molecules had been formed
including ethanoic acid, lactic acid
and urea
Later similar experiments were
done using CO2 that produced
nucleotides.
10. Conclusion
These experiments cannot reproduce the exact
conditions on the primitive Earth
We shall never know exactly what happened
But it can be shown that the basic building
blocks for the large macromolecules can be
synthesised in vitro from inorganic
compounds.
11. How Do Microbes Arise?
By 1860, the debate had become so heated
that the Paris Academy of Sciences offered a
prize for any experiments that would help
resolve this conflict
The prize was claimed in 1864 by Louis
Pasteur, as he published the results of an
experiment he did to disproved spontaneous
generation in microscopic organisms
12. Spontaneous Generation
For centuries, people based their beliefs on
their interpretations of what they saw going
on in the world around them without testing
their ideas
They didn’t use the scientific method to arrive
at answers to their questions
Their conclusions were based on untested
observations
13. Aristotle (384 –322 BC)
Proposed the theory of
spontaneous generation
Also called abiogenesis
Idea that living things can
arise from nonliving matter
Idea lasted almost 2000 years
15. Francesco Redi (1668)
In 1668, Francesco Redi, an Italian
physician, did an experiment with flies
and wide-mouth jars containing meat
16. Redi’s Experiment
Redi used open & closed flasks which
contained meat.
His hypothesis was that rotten meat does not
turn into flies.
He observed these flasks to see in which
one(s) maggots would develop.
17. Redi’s (1626-1697) Experiments
Evidence against spontaneous generation:
1. Unsealed – maggots on meat
2. Sealed – no maggots on meat
3. Gauze – few maggots on gauze, none on meat
18. Redi’s Findings
He found that if a flask was closed with a lid so
adult flies could not get in, no maggots
developed on the rotting meat within.
In a flask without a lid, maggots soon were
seen in the meat because adult flies had laid
eggs and more adult flies soon appeared.
19. Results of Redi’s Experiments
The results of this experiment
disproved the idea of
spontaneous generation for
larger organisms, but people
still thought microscopic
organisms like algae or
bacteria could arise that way.
22. 22
Needham’s Results
copyright cmassengale
Needham’s experiments seemed to support the
idea of spontaneous generation
People didn’t realize bacteria were already
present in Needham’s soups
Needham didn’t boil long enough to kill the
microbes
25. Microbes come from cells of
organisms on dust particles in
the air; not the air itself.
Pasteur put broth into several
special S-shaped flasks
Each flask was boiled and placed
at various locations
Pasteur's Hypothesis
27. Flask left at various locations
Did not turn cloudy
Microbes not found
Notice the dust that collected in
the neck of the flask
28. Pasteur's Experiment
Pasteur’s S-shaped flask kept microbes out but let air in.
Proved microbes only come from other microbes (life
from life) - biogenesis
