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History of Life
Chapter 14
Biogenesis
All living things come from other living
things
Spontaneous generation
• The idea that living things could also arise
from nonliving things.
Francesco Redi
• His experiments
showed that maggots
came from flies
• One open jar and one
closed jar
• Meat had maggots in
the open jar but not
the closed jar
Lazzaro Spallanzani
• His experiments showed that
microorganisms are in the air around us.
• Boiled broth in two flasks – covered one
and left the other open – microorganisms
appeared in the open flask
Louis Pasteur
• His experiments
helped to prove
biogenesis and get rid
of the idea of
spontaneous
generation.
• Used curved neck
flasks and broth
EARTH’S HISTORY
The Formation of Earth
• The estimated age of earth is about 4 billion
years old. This was determined by studying
the many layers of earth surface.
Radiometric dating
• Method for determining the age of materials
Isotopes
• Atoms of the same element that differ in the
number of neutrons they contain. Most
elements have several isotopes.
• Mass number of an isotope is the total
number of protons and neutrons in the
nucleus
• Isotopes are designated by their chemical
name followed by their mass number.
– Example: carbon exists as both carbon-12 and
carbon-14
Radioactive decay –
• the nuclei of an
isotope release
particles or radiant
energy, or both,
until the nuclei
become stable.
Such isotopes are
called radioactive
isotopes.
Half-life –
the length of time it
takes for one-half
of any size sample
of an isotope to
decay to a stable
form.
Alexander Oparin
and John Haldane
Hypothesized about how the first organic
compounds were assembled from earth’s
early atomosphere
Stanley Miller and Harold Urey
• Used Oparin’s
hypothesis to set up an
experiment and
synthesize organic
compounds including
amino acids in the lab
Sidney Fox
• Research on physical structures that may
have given rise to the first cells
• Cell like structures form spontaneously in
the lab from solutions of simple organic
chemicals
• Microspheres – spherical in shape and are
composed of many protein molecules that
are organized as a membrane
• Coacervates – collections of droplets that
are composed of molecules of different
types, including lipids, amino acids, and
sugars
• These studies suggest that the gap between
the nonliving chemical compounds and
cellular life may not be quite as wide as
previously thought
• However, microspheres and coacervates do
not have all of the properties of life.
THE FIRST LIFE FORMS
The First Cells
The first cells were probably anaerobic,
heterotrophic prokaryotes
The First Cells
• Archaea – related group of unicellular
organisms, many of which thrive under
extremely harsh environmental conditions
• Many species of archaea are autotrophs that
obtain energy by chemosynthesis instead of
photosynthesis
The First Cells
• Some forms of life had become
photosynthetic by 3 billion years ago
• Oxygen is a byproduct of photosynthesis
• Ozone formed in the upper atmosphere to
help protect the earth from ultraviolet
radiation
The First Eukaryotes
• Endosymbiosis – about 1.5 to 2 billions
years ago, a type of small aerobic
prokaryote was engulfed by and began to
live and reproduce inside a larger, anaerobic
prokaryote.
• The eukaryotes provided a beneficial
environment, and the prokaryotes provided
a method of energy synthesis.