History of Life
Chapter 14
Biogenesis
•Biogenesis is the principle that
all living things come from
other living things
•Spontaneous generation is the
belief that living things arise
from non-living things
• Back in seventeenth century
this was the explanation why
maggots arise from rotten
meat and fish appear in
ponds
Francesco Redi
•Italian scientist (1626-1697) that noticed and described the
different forms of flies
•Observed maggots turned into oval cases and flies emerge
Also observed maggots appear where adult flies landed
•Created an experiment to prove his hypothesis that flies
emerge from maggots
Francesco Redi’s Experiment
Jars were set up with meat inside and allowed to rot
Control group
The jars were exposed to the environment and not covered at
Experimental group
Jars were covered with cloth so air can flow through, but
organisms cannot enter or leave
Francesco Redi’s Experiment
Results
The uncovered jars that were exposed to flies had maggots
growing that eventually turned into flies
The covered jars did not have any maggots or flies inside
Lazzaro Spallanzani
Italian scientist (1729-1799) that used microscopes to
observe microorganisms that could explain biogenesis
At this time, it was believed that “vital force” was how
microorganisms arise from the air
Hypothesized that microorganisms formed from preexisting microorganisms
Created an experiment to test his hypothesis
Lazzaro Spallanzani’s Experiment
Boiled clear, fresh broth until
the flasks filled with steam
Control group
Flask was remained open
during experiment time
Experimental group
Flask was immediately
covered before cooling so not
to allow air or bacteria to
enter
Lazzaro Spallanzani’s Experiment
Results
The uncovered flask
(control group) became
contaminated with
microorganisms when air
entered
The experimental group
flask did not have any
growth
Scientists believed that
boiling the broth killed the
“vital force” and still
continued to believe
spontaneous generation
Louis Pasteur
French scientist (1822-1895) created an experiment to
answer objections of Spallanzani’s experiment
Made a curved neck flask that allowed air into the
flask, but prevented microorganisms to enter
Louis Pasteur’s Experiment
Started the experiment by boiling broth in the curved neck flask to kill
any microorganisms inside
Left the flask to sit for one year – the broth was still clear
After a year, the neck of the flask was broken
Results
After one day being exposed to the air, the broth became
contaminated with microorganisms
These results provided evidence for biogenesis and that spontaneous
generation was not possible
Formation of Earth
Earth’s Age
The estimated age of the Earth is 4.5 billion years old
Scientists are able to explore the surface and its layers to
study its geology and determine age
Formation of Earth
Radiometric Dating
A method of establishing the age of materials
Using isotopes (elements with more or less
neutrons) of specific elements, scientists can date
the age of rocks and fossils more accurately
Mass number = protons + neutrons
Isotopes have a different mass number due to change in
neutrons
Radioactive decay – when isotopes have an unstable
nuclei they release energy that we can calculate
Formation of Earth
Half-life
The length of time it takes for one-half of the same size of the
isotope to decay to a stable form
Carbon-14
All living things contain the isotope Carbon-14 in their cells
As they die, Carbon-14 decays into Carbon-12 at a known rate
that scientists can calculate and determine the age of the
organism
Organisms that are much older, scientists use different isotopes
Alexander Oparin & John Haldane
Soviet and American scientists that were able to determine the
inorganic compounds found in the early atmosphere
They believed it contained
Ammonia (NH3)
Hydrogen gas (H2)
Water vapor (H2O)
Methane (CH4)
Stanley Miller & Harold Urey
American scientists that
created an experiment to
explain how inorganic
compounds that existed on
Earth created our known
atmosphere
Set up a chamber containing
gases and allowed them to
circulate with electric shock
Results
After going through
experiment the end results
were organic compounds
that make up the modern
day atmosphere
Origin of Heredity
First cells
The oldest known fossils that are thought to be cells are the
size and shape of some living bacteria
Scientists believe that RNA was the first nucleic acid on Earth
Chemosynthesis
Archaea – related group of organisms that can survive under
harsh conditions
Chemosynthesis – when CO2 serves as the source of energy
as well as inorganic molecules like sulfur
Origin of Heredity
Photosynthesis & Aerobic Respiration
The ability for organisms to use inorganic matter and create
oxygen gas
Cyanobacteria – most likely the earliest bacteria that created
oxygen gas as a byproduct and release it into the atmosphere
After billions of years of oxygen gas forming and filling the
atmosphere, O atoms reacted with O2 to form O3 which is our
ozone
Without our ozone the UV light from the sun would damage our DNA
and life could not have come to exist
The First Eukaryotes
Eukaryotes
Larger than prokaryotes
DNA is organized into chromosomes
Contain cytoskeleton and nucleus
Endosymbiosis
Theory that modern day organelles were engulfed by ancient
eukaryotes and later became part of the cell’s function
Ex: chloroplast and mitochondria (contain their own DNA)