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The Origin of Life
Chapter 14
The Beginning:
Earth is about 4.6 billion years old
Life began on Earth about 3.5 billion years ago
in the ocean
Evidence of Life:
Fossils: remains of organisms, found
in sedimentary rock
 Relative Dating: lower rocks are older
than higher ones
 Radiometric Dating: using radioactive
isotopes in rocks because rate of
decay is related to half-life
Relative Dating:
Radiometric Dating:
How does life arise?
Spontaneous generation: life
from nonliving things
– Francesco Redi: disproved theory
by showing that flies must come
from other flies
How does life Arise?
Spontaneous generation:
– Louis Pasteur: concluded that microorganisms
must come from other microorganisms using Sshaped flasks that let in only air = no organisms
Biogenesis: life only from other living things
– Miller & Urey: showed that organic molecules
could have formed the beginning of life
The origin of cells:
Anaerobic prokaryotes: lived in an
atmosphere with no oxygen
The origin of cells:
Aerobic organisms: evolved once
photosynthesis released oxygen
The origin of cells:
Prokaryotes: cells without a nucleus or
Eukaryotes: cells with a nucleus and
– cells grew in complexity once conditions for life
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