The document outlines the key processes thought to be necessary for the spontaneous origin of life on Earth: 1) The synthesis of simple organic molecules, as demonstrated by the Miller-Urey experiment; 2) The assembly of these molecules into polymers like polypeptides; 3) A mechanism for inheritance, proposed to be self-replicating RNA; 4) The development of membranes. These processes are hypothesized to have led to the formation of "protobionts", early cell-like structures surrounded by membranes. The endosymbiotic theory proposes that eukaryotic cells arose from engulfed prokaryotes that evolved to become organelles like mitochondria and chloroplasts. Early prokaryotes also produced oxygen as

1. Option D: Evolution
D1 Origin of life on Earth

2. What you need to be able
to do and understand:
D.1.1 Describe four processes
needed for the spontaneous
origin of life on Earth.
D.1.2 Outline the experiments
of Miller and Urey into the
origin of organic compounds.
D.1.3 State that comets may
have delivered organic
compounds to Earth.
D.1.4 Discuss possible
locations where conditions
would have allowed the
synthesis of organic
compounds.
D.1.5 Outline two properties of
RNA that would have allowed it
to play a role in the origin of life.
D.1.6 State that living cells may
have been preceded by
protobionts, with an internal
chemical environment different
from their surroundings.
D.1.7 Outline the contribution of
prokaryotes to the creation of
an oxygen-rich atmosphere.
D.1.8 Discuss the
endosymbiotic theory for the
origin of eukaryotes.

3. Imagine what it would
take to create life.
What do you need?

4. Spontaneous
origin?
If cells can only come from existing cells (the cell
theory) when and where did the first cells come from?
The oldest undisputed bacteria
fossil dates back 1.9 billion
years ago
Gunflint microfossil
Eosphaera 20 microns
across.
A recipe for cell-like structures:
1. Simple organic molecules need to be available
(amino acids need to be made from
water, carbon dioxide and ammonia)
2. Simple molecules need to be assembled into
polymers (polypeptides from amino acids)
3. A mechanism that makes inheritance possible
(self-replication is needed)
4. Development of membranes (to form with an
internal chemistry different than their
surroundings)

5. 1- Simple organic molecules
Miller and Urey
http://bcs.whfreeman.com/thelifewire/
content/chp03/0302001.html
They investigated the theory that organic compounds could
have formed spontaneously on Earth.
Watch this
tutorial:
In Miller’s own words…

6. So what did Miller and Urey conclude?
Organic compounds could have formed
spontaneously on Earth, before there were any
living organisms here.
http://www.ucsd.tv/miller-urey/
Now do your own experiment to create amino
acids

7. Where were the first
organic compounds
synthesized?
From the experiments of Miller and
Urey- in the atmosphere, in water, or
on the surface of the Earth
Hydrothermal vents with the
chemicals from the interior of the
Earth
Delivered by meteorites.
Extraterrestrial origins for organic
compounds- NASA conducted
experiments showing that organic
compounds could have formed in
cold interstellar space.
Certain categories of
meteorites are rich in carbon
and some of these meteorites
have been found to contain
many of the same amino
acids found in the Miller-Urey
experiment

8. Data
analysis
question
Read this paper for
more information:
http://www.lpi.usra.ed
u/publications/MSR/B
ada/BadaAbs.html
Amino Acid Murchison
meteorite
Miller-Urey
experiment
Glycine  
Alanice  
α-amino-N-butyric acid  
α-aminoisobutyric acid  
Valine  
Norvaline  
Isovaline  
Proline  
Popecolic acid  
Aspartic acid  
N-ethylglycine  
Sarcosine  
1. Compare the
amino acids found
in the meteorite
with those
produced in the
Miller-Urey
experiment. Refer
to named
examples [3]
2. Suggest a
conclusion based
on your
comparison. [1]

9. Hydrothermal vents
Another theory suggests that life may
have arisen at ancient volcanic vents.
This environment provides the necessary
gasses, energy, and a possible source of
catalysts (metal sulfides).
Read this site for a summary of
what is known to date:
http://www.chem.duke.edu/~jds/cr
uise_chem/Exobiology/sites.html

10. 2- assembled into polymers
(polypeptides from amino
acids)
Polymerization –
monomers to
polymers

11. 3- A mechanism that makes inheritance
possible (self-replication is needed)
RNA almost certainly preceded DNA
as the genetic material
Self-replication – RNA to RNA
RNA has two key abilities that make it the likely original genetic material
•genetically: self-replication
•enzymatically: catalyzing chemical reactions
Read this article on
RNA:
http://www.nytimes.com/
2009/05/14/science/14rn
a.html
Genes cannot be made/
replicated without
enzymes and enzymes
cannot be made without
genes. Therefore how did
it all start?

12. self-replication of RNA
RNA has been experimentally shown to
have the ability to self-replicate – one
molecule can be the template for the
production of another molecule.
Individual RNA nucleotides self-assemble
into RNA polymers because of
complementary nucleotide bases
A=U
G=C
RNA nucleotide sequence is
variable, thus allowing for diversity.
Self-replication allows for the inheritance
of information coding for amino acid
sequences in polypeptides and
transmitting genetic information between
generations

13. RNA can
catalyze
chemical
reactionsRNA can act as an enzyme, catalyzing
various reactions, producing polymers from
monomers in eukaryotic organisms today.
RNA regulates numerous cellular
functions, including protein synthesis
and gene control.
For example, RNA ribozymes are
found in modern cell
RNA can self- replicate
An interview with Dr.
Thomas Cech- talking
about what RNA can do.
He won the Nobel prize
in Chemistry in 1989

14. 4- Development of membranes- creating an internal
chemistry different from the external
A spherical vesicle composed of a bilayer
membrane form spontaneously from
phospholipids.
coacervates
A spherical aggregation of lipid molecules making up a
colloidal inclusion which are held together by hydrophobic
forces. They form spontaneously from certain dilute
organic solutions. Generally 1 to 100 micrometers in
diameter and possess osmotic properties.
microsphere
sThey form spontaneously from
heated and cooled amino acids and
exhibit some properties associated
with life (response to the
environment, basic metabolism and
simple reproduction)
liposom
es
See for more information: http://www.biog1105-
1106.org/demos/106/unit04/3a.protobionts.html

15. The result of the
recipe?“Protobionts:" the product of the four processes
which are cell-like structures.
They are an aggregate of abiotically produced
organic molecules surrounded by a membrane or
a membrane-like structure.
Protobionts exhibit some of the properties
associated with life, including simple
reproduction, metabolism and excitability, as well
as the maintenance of an internal chemical
environment different from that of their
surroundings.
Experiments by Sidney W. Fox and
Aleksandr Oparin have
demonstrated that they may be
formed spontaneously, in conditions
similar to the environment thought to
exist on an early Earth.
Fox dripped organic monomers onto hot sand, clay, and rock. The water vaporized
and left behind polypeptides he called proteinoids. Clay was abundant in prebiotic
earth and has the ability to act as a substrate. The charged sites on the clay attracted
monomers in such concentrations to bring them into close proximity for chemical
binding.
Once these organic compounds were produced, aggregates self-assembled into
small spheres called protobionts. These small spheres were capable of osmotic
swelling and shrinking and even able to produce a membrane potential.
http://www.siuc.edu/~
protocell/

16. Endosymbiotic theory be eaten and
survive…
Eukaryotic cells appear to have evolved from
prokaryotic ancestry as a smaller prokaryote
within a larger prokaryote and then
coexisted.
Evidence:
Mitochondria and chloroplasts both
have double membranes where the
second outer membrane is from the
host, therefore it might have been
“eaten”.Mitochondria and chloroplasts both have a
loop of naked DNA that lacks histone
proteins, as do prokaryotes.
Mitochondria and chloroplasts both divide by binary fission which is independent of
nuclear division.
Mitochondria and chloroplasts both have smaller 70S ribosomes which are similar
to prokaryotes and different from 80S eukaryotic ribosomes.
Chloroplast thylakoids are similar to cyanobacterial photosynthetic structures.
Chlorophyll a is the main photosynthetic pigment for both chloroplasts and
prokaryotes.

17. What did prokaryotes give to
us?
The first pollution
crisis
However, oxygen is a powerful degrader of
organic compounds. Even today, many bacteria
and protists are killed by oxygen. Organisms had
to evolve biochemical methods for rendering
oxygen harmless; one of these
methods, oxidative respiration, had the
advantage of producing large amounts of energy
for the cell, and is now found in most eukaryotes.
Where was this oxygen coming from?
Cyanobacteria, photosynthetic organisms that
produce oxygen as a byproduct, had first
appeared 3.5 billion years ago, but became
common and widespread in the Proterozoic era.
The first "pollution crisis" hit the Earth about 2.2 billion
years ago. Several pieces of evidence -- the presence of
iron oxides in paleosols (fossil soils), the appearance of
"red beds" containing metal oxides, and others -- point to
a fairly rapid increase in levels of oxygen in the
atmosphere at about this time.
Holland, H.D. 1994. Early Proterozoic atmospheric
change. Pp. 237-244. In: Bengtson, S. (ed.) Early Life on
Earth. Columbia University Press, New York.
Oxygen levels in the Archaean had been less that 1% of present levels in the
atmosphere, but by about 1.8 billion years ago, oxygen levels were greater than 15% of
present levels and rising. (Holland, 1994). It may seem strange to call this a "pollution
crisis," since most of the organisms that we are familiar with not only tolerate but require
oxygen to live.

18. A good summary of everything we
have done so far:
http://www.plosbiology.org/article/info:
doi/10.1371/journal.pbio.0030396
When Art and Science collide, you get the
Big Bang and the Origins of Life, as
interpreted by the amazing street art
animators, Blu.