Transcript Steady-State Theory

History of Life on Earth
Mike Yeoman
9th Grade Biology
Two Opposing Scientific Viewpoints
• Steady-State Theory: Developed in 1948
to oppose the Big Bang. Also called the
Infinite Universe Theory. Has since been
disproven.
• Big Bang Theory: Proposed as early as
1912, it is the theory with the most
evidence and best explains the current
state of the universe.
Steady-State Theory
• Alternative to the “Big Bang”
• Implies there was no beginning and no
end of the universe.
• New matter must constantly be created.
(cannot explain quasars and radio galaxies)
• Requires an “antigravity” force.
• Cannot explain cosmic background
radiation.
Big Bang Theory:
Three Pillars
• Hubble-type expansion of the universe.
Includes redshifts that are interpretted as a
Doppler shift.
• Cosmic microwave background radiation
left over from the initial expansion.
• Abundance of simple atoms like Hydrogen
and Helium as a result of nucleosynthesis.
• Radiometric dating is used to estimate the age
of a substance.
• Half-life is the amount of time it takes for half of
the radioisotope to decay.
• The Miller-Urey
experiment showed
that organic
compounds.
• Two major
problems: ammonia
and methane were
probably not
present; there was
no ozone to protect
the molecules from
UV radiation.
Precursors of the First Cells
• The Miller-Urey experiment and Lerman’s
Bubble Model show that it’s possible and gave
pathways that could have produced amino
acids, lipids, and hydrocarbons.
• RNA can form spontaneously in water.
• Messenger RNA acts as an informational
storage molecule.
• Hypothesis: RNA was the first self-replicating
information-storage molecule and it catalyzed
the assembly of the first proteins.
Formation of Cell Membrane
• Certain lipids, when combined with other molecules, can
form a tiny droplet whose surface resembles a cell
membrane.
• Lab experiments show that in water, short chains of
amino acids can form tiny droplets called microspheres.
• Another type of droplet made of linked amino acids and
sugars is called a coacervate.
• Microspheres are first step towards cellular organization.
• Longer lasting microspheres would have become more
common.
• Microspheres are not true cells unless they have the
characteristics of living things, including heredity.
• Scientists agree that double-stranded DNA probably
came from RNA.
Evolution of Cellular Life
• Scientists study the best evidence of early life, fossils
(preserved or mineralized remains).
• Marine cyanobacteria are photosynthetic bacteria that
produced oxygen in the Earth’s oceans.
• Two types of bacteria evolved from this: eubacteria and
archaebacteria
• Eubacteria are prokaryotes that contain peptidoglycan in
their walls. (Common bacteria)
• Archaebacteria lack peptidoglycan and have unique
lipids
Evolution of Eukaryotes
• The first eukaryotes appeared 1.5 billion
years ago.
• Eukaryotes are much larger than
prokaryotes.
• Almost all eukaryotes have mitochondria.
• Only plants and protists have chloroplasts.
• Mitochondria and chloroplasts are the size
of prokaryotes and contain their own DNA
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Size and Structure
Genetic Material
Ribosomes
Reproduction
• Six Kingdoms include: Eubacteria,
Archaebacteria, Protists, Fungi, Plants,
and Animals.
• Protists are often times unicellular and
nonspecialized.
• Some are like animals, some carry out
photosynthesis.
• Protists make up about half of the biomass
of the Earth.
• Burgess Shale shows creatures from “Cambrian
Explosion” 505 to 438 mya
• Mass extinction about 440 mya where a large
percentage of species were wiped out.
• 5 mass extinctions throughout history.
• Possible current mass extinction.
Life Invaded the Land
• Ancient cyanobacteria
produced oxygen,
some of which became
ozone. Ozone
enabled organisms to
live on land.
• Plants and Fungi
formed mycorrhizae
and were the first
multicellular organisms
to live on land.
• Arthropods were the
first animals to leave
the ocean.
More Life on Land
• The first vertebrates to
invade dry land were
amphibians.
• The extinction of many
reptile species enabled
birds and mammals to
become the dominant
vertebrates on land.
• The movement of the
continents on the
surface of the Earth has
contributed to the
geographic distribution
of some species.