Download The Origin of Life

The Origin of
Life
-AP Biology What you need to know….
Enduring understanding 1.D: The origin of living
systems 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 generating
complex organic molecules and
simple cell-like structures.
Ex. Miller-Urey Experiment
The “organic soup” model, the hypothesized primitive atmosphere contained
inorganic precursors from which organic molecules could have been synthesized
through natural chemical reactions catalyzed by the input of energy.
In turn, these molecules served as
monomers (building blocks) for the
formation of more complex
molecules, including amino acids
and nucleotides.
Some models suggest that primitive life developed on biogenic
surfaces, such as clay, that served as templates and catalysts for
assembly of macromolecules.
Under laboratory
conditions, complex
polymers and selfreplicating molecules (DNA
or RNA) can spontaneously
assemble. It remains an
open question whether the
first genetic and selfreplicating material was
DNA or RNA.
The RNA World
hypothesis proposes that
RNA could have been the
earliest genetic material.
Source:
http://evolution.berkeley.edu/evosite/evo101/IIE2bStudyorigins.sht
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Quick Review of the Steps
that Would Give Rise to the
First Cell
1. Monomers
2. Macromolecules
3. Plasma membrane
4. Self Replication
(DNA or RNA)
The Age of the Earth
Earth formed about 4.6
billion years ago (bya)
and was too hostile for life
First evidence of life at
3.5 bya
**The earth is very old!**
The fossil record provides a timeline for the
appearance of organisms on the planet.
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