The History of Life

1
The History of Life
2
Early History of Earth

• Early Earth was inhospitable!
• It was probably very hot, volcanoes might have
  erupted frequently spewing gases and lava
• These gases helped form Earths early atmosphere
  which contained little oxygen but abundant carbon
  dioxide and nitrogen
• About 3.9 billion years ago, earth might have
  cooled enough for water in the atmosphere to
  condense
• This would have led to millions of years of
  rainstorms, enough to fill Earths oceans
• It is in the oceans that scientist propose that
  the first organisms appeared between 3.9 and 3.5
  billion years ago

3
History in Rocks

• Scientist cannot be sure that earth formed in
  this way. There is no direct evidence of the
  earliest years of Earths history.
• The physical processes of Earth constantly
  destroy and reform rock.
• The oldest rocks that have been found on earth
  formed only about 3.9 billion years ago
• Rocks are an important source of information
  about the diversity of life that once existed on
  the planet

4
Fossils Clues to the Past

• The millions of species that live today are
  probably only a small fraction of all the species
  that ever existed.
• About 99 of species are extinct they no longer
  live on Earth
• Fossil evidence of an organism that lived long
  ago.
• Scientists use fossils to learn about ancient
  species.

5
The Origin of Life

• Francesco Redis experiment (1668)
• How do the results differ in the two jars?
• What might you conclude from these results?
• Louis Pasteurs experiment finally disproved
  spontaneous generation (mid 1800s)

6
Which came first, the chicken or the egg?

• Biologists have accepted the concepts of
  biogenesis for more than 100 years
• Biogenesis does not answer the question of how
  life began on Earth
• No one will ever know for certain how life began
  on earth. We can only make hypotheses about
  conditions on early Earth.

7
How does chemistry become life??

• Evolution of complex molecules

8
Primordial Soup

• Step 1 simple organic molecules must have formed
  (molecules that contain carbon)
• Step 2 Simple organic molecules must have become
  organized into complex organic molecules
  (proteins, carbohydrates, and nucleic acids)
• 1930s Oparin (Russian) hypothesized that life
  began in the oceans
• Energy from sun and lightning triggered chemical
  reactions to produce small organic molecules from
  substances in the atmosphere
• 1953 Miller and Urey (American) replicated
  conditions in the lab and produced amino acids,
  sugars, and other molecules

9
The next step

• How did we get from simple organic compounds to
  complex organic compounds?
• In the presence of heat, without oxygen, amino
  acids link to from proteins. ATP is produced in
  a similar way.
• Sidney Fox found that if you continued to heat
  the complex organic compounds protocells
  developed.

10
The Evolution of Cells

• The first true cells
• Prokaryotes that evolved from a protocell
• Anaerobic (no oxygen present in atmosphere)
• Food organic molecules abundant in oceans
• Autotrophs evolved to inhabit harsh conditions
  (ie. Archaebacteria)

11
Endosymbiont Theory

• Eukaryotes probably evolved from prokaryote cells
• Theory proposes that eukaryotes evolved through a
  symbiotic relationship between prokaryotes
• Evidence
• Chloroplast and cyanobacteria resemble
  eachother
• mitochondria and bacteria some look similar
• Chloroplast and mitochondria contain DNA that is
  similar to the DNA in prokaryotes
• Today, some prokaryotes live in close association
  with eukaryotes

12
Life Today

• Could new life originate on Earth today?
• List the specific evidence that supports each
  conclusion.
• Life comes from existing life
• Life probably originated on Earth through the
  reaction of chemicals in Earths atmosphere and
  their further reaction on Earths surface
• Cells probably evolved as the chemicals on early
  Earth became more organized.