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Chapter 14
The History of Life
History in Rocks
• It is believed that the earth is about 4.6 billion
years old.
• The oldest rocks that have been found on
Earth formed about 3.9 billion years ago.
• Fossils (evidence of an organisms that lived
long ago) tell us information about the earth.
How Fossils Form
• 1. Trace fossils – a marking left by an animal
and may include a footprint, a trail, or a
burrow.
• 2. Casts – when minerals in rocks fill a decayed
organism, they make a replica, or cast, of the
organism.
• 3. Petrified fossils – minerals sometimes
penetrate and replace the hard parts of an
organism, producing copies of them.
• 4. Imprints – a thin object that falls into
sediment can leave an imprint when the
sediment hardens into rock.
• 5. Amber-preserved and frozen fossils – an
entire organism was quickly trapped in ice or
tree sap that hardened into amber.
• 6. Molds – when an organism is buried in
sediment and then decays, leaving an empty
space.
The Age of a Fossil
• Relative dating – If the rock layers have not
been disturbed, the layers at the surface must
be younger than the deep layers.
• Scientists can determine the order of
appearance and extinction of the species that
formed fossils in the layers.
Radiometric dating
• Scientists use radiometric dating techniques
utilizing the radioactive isotopes in rocks or
fossils.
Radioactive parent isotopes and their stable
daughter products
Radioactive Parent
Stable Daughter
Potassium 40
Argon 40
Uranium 235
Lead 207
Uranium 238
Lead 206
Carbon 14
Nitrogen 14
Rubidium 87
Strontium 87
Thorium 232
Lead 208
The Origin of Life
Early Ideas
• Spontaneous generation – the idea that
nonliving material can produce life.
Meat left out
decaying,
“produced”
maggots.
Francsco Redi’s
experiment
disproved this idea.
• Many scientists still believed that
microorganisms (bacteria) could
spontaneously be produced.
• Louis Pasteur’s experiment disproved this
idea.
The Origin of Life
Modern Ideas
• Biogenesis – living organisms come only from
other living organisms.
• In 1953, Miller and Urey performed an
experiment to see if the conditions of early
earth could produce organic (carbon
containing) molecules.
• After a week of performing their experiment,
several kinds of amino acids and sugars
appeared.
The Origin of Life
• Sidney Fox performed experiments to see if
these complex organic molecules could
combine to produce cells.
• He was able to produce protocells after
heating the organic molecules.
• Protocells – a large, ordered structure,
enclosed by a membrane, that carriers out
some life activities, such as growth and
division.
Protocell
RNA
Phospolipid
bilayer
The First True Cells
• The first cells are thought to have been
heterotrophic prokaryotes. They used the
organic molecules for food that were
abundant on earth.
• However, when the organic molecules were
gone, autotrophic prokaryotes became
abundant and used chemosynthesis to make
glucose.
• Next probably came the photosynthetic
prokaryotes that used sunlight to make
glucose.
• These organisms produced oxygen and
affected life on earth.
Endosymbiont theory
• Complex eukaryotes probably evolved from
prokaryotes that incorporated mitochondria
and chloroplasts for their energy making
ability.
• Mitochondria and chloroplasts have DNA
similar to prokaryotes.