Download The origin of life is explained by natural processes.

The Origin of
Life
Where did it all begin?
Keeping in mind that all of this
started a LOOOONG time ago,
here’s what we know….
Enduring understanding 1.D: The origin of life is
explained by natural processes.
The process of evolution explains
the diversity and unity of life. A
number of experimental
investigations have provided
evidence that the conditions early
in the Earth’s history provided an
environment capable of selfgenerating complex organic
molecules and simple cell-like
structures.
Ex. Miller-Urey Experiment
Miller-Urey’s experiment coined the “organic soup” model, hypothesized that the primitive
atmosphere contained inorganic precursors from which organic molecules could have been
synthesized through natural chemical reactions catalyzed by the input of energy from the
environment. Basically, the chemicals that build the macromolecules needed for life were
already there in the ocean, and the lack of oxygen in the environment combined with energy
from severe lightning storms allowed the first living molecules to self assemble and start the
chain of events that led to where we are today. Spontaneous generation through chemistry.
In turn, these molecules served as
monomers (building blocks) for the
formation of more complex molecules,
including amino acids and nucleotides,
that eventually became cells.
Some models suggest that primitive life developed on biogenic
surfaces, such as clay, that served as templates and catalysts for
assembly of macromolecules. (Again, the perfect chemistry at the
perfect time.)
Under laboratory
conditions, complex
polymers and selfreplicating molecules (DNA
or RNA) can spontaneously
assemble. Although, it
remains an open question
whether the first genetic
and self-replicating material
was DNA or RNA.
What was the first genetic
material? DNA or RNA?
The RNA World hypothesis
proposes that RNA could have
been the earliest genetic
material. From the structures of
the molecules, it’s logical to
conclude individual RNA
strands could link up to form
DNA molecules in order to
create storage of information
on how to make a group of
proteins for future reference.
Source:
http://evolution.berkeley.edu/evosite/evo101/IIE2bStudyorigins.sht
ml
Quick Review of the Steps that Would Give
Rise to the First Cell thanks to the Chemistry
of early earth
1. Chemicals assembled into Monomers
2. Monomers grouped to form
Macromolecules
3. Macromolecules grouped to create early
cells (prokaryotes)
4. Macromolecules are able to self replicate
which lead to more cells with the same traits
5. Mutations and changes lead to variation
6. Endosymbiosis lead to eukaryotes
7. Colonial eukaryotes lead to multicellular
organisms and specialized structures.
The Age of the Earth
All of this is difficult to study,
because of how long ago it
happened. (Earth formed
about 4.6 billion years ago
[bya] and was too hostile for
life for quite some time. The
first evidence of life
(prokaryotes) in the fossil
record appears at 3.5 bya).
**The earth is very old!**
The fossil record provides our best timeline for
the appearance of organisms on the planet.
Fossil Record Example
• While every major group (plants, protists, fungi, prokaryotes, and
animals) have a pathway of evolution that can be traced through the
fossil record, we are going to look at animals as an example. Notice
how the order that each major group was found builds on complexity
and there is evidence of homology between the groups.
• Animal Timeline (from earliest to most recent): Animal-Like Protists
(ex: amoebas) colonial animal-like protists 
Jellyfish/Sponges/Corals  Fish with no bones (sharks)  Fish with
bones  Amphibians  Reptiles  Birds and Mammals
Sample Question (AP Test)
Fossils of lobe-finned fishes, which are ancestors of amphibians, are found in rocks that are
at least 380 million years old. Fossils of the oldest amphibian-like vertebrate animals with
true legs and lungs are found in rocks that are approximately 363 million years old.
Three samples of rocks are available that might contain fossils of a transitional species
between lobe-finned fishes and amphibians: one rock sample that is 350 million years old,
one that is 370 million years old, and one that is 390 million years old.
(a) Select the most appropriate sample of rocks in which to search for a transitional species
between lobe-finned fishes and amphibians. Justify your selection.
(b) Describe TWO pieces of evidence provided by fossils of a transitional species that would
support a hypothesis that amphibians evolved from lobe-finned fishes.
PRACTICE: Discuss how each of the following
influenced the origin of living organisms.
a) primordial atmosphere
b) photosynthesis
c) endosymbiosis theory
d) RNA world hypothesis
ANSWERS: Discuss how each of the following
influenced the origin of living organisms.
a) primordial atmosphere – conditions were right in early earth for
organic molecules to form
b) photosynthesis – the evolution of photosynthetic prokaryotes added
oxygen to the atmosphere and “cleaned up” the hostile atmosphere for
life to move onto land
c) endosymbiosis theory – eukaryotes evolved from prokaryotes that
formed “mega cells” and membrane folding to create organelles
d) RNA world hypothesis – self-replicating RNA was the first nucleic
acid to form. DNA evolved later as a “gene storage” mechanism from
pieces of RNA that combined