Earth

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• Chapter 17.2
• Earths Early History

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Age of the Earth

• It is estimated that the Earth
• is 4.6 billion years old
• Theories of how the Earth was born vary (IE
  the Big Bang Theory)
• Elements arranged themselves according to density
• ?Least dense make up the atmosphere, most dense
  make up the core

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Earths Early Atmosphere

• Earths early atmosphere probably contained
  hydrogen cyanide, carbon dioxide, carbon
  monoxide, nitrogen, hydrogen sulfide, and water
• All toxic gases except the
• water

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The Early Earth

• It wasnt until 4 billion years ago that the
  first solid rocks formed
• It wasnt until 3.8 billion years ago that the
  Earth was cool enough to have liquid water
• So this is when the first oceans formed

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Formation of Organic Molecules

• Early atmosphere allowed the formation of organic
  molecules
• Did not have oxygen
• Would not form in todays atmosphere
• Oxygen is too reactive
• Bacteria would eat the molecules

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Miller and Urey

• Stanley Miller and Harold Urey attempted to
  answer what the
• Earths early atmosphere and
• how life began
• Filled an enclosed flask with
• hydrogen methane, ammonia,
• and water to represent the
• atmosphere
• Passed electricity through
• this mixture

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The Results

• Amino acids began to form after a couple days
• Extensions of their experiments have also shown
  to make nucleotides
• Scientists think that these were the first steps
  to life

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The First Cells

• Thought to have originated 200-300 million years
  after oceans formed
• Earliest cells called proteinoid microspheres
  were created when organic molecules became
  trapped in bubbles
• ?Not alive but have some
• characteristics of living cells

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Oxygen-Free Life Forms

• The first life forms are thought to have evolved
  in oxygen free environments approximately 3.5
  billion years ago
• Photosynthetic organisms evolved
• in the oceans approximately 2.2 billion
• years ago
• ?Started pumping oxygen into the
• atmosphere

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Rusty Oceans

• When oxygen mixed with iron in the water, the
  oceans began to rust
• The iron oxide sank to the bottom of the oceans
  giving us the iron ore deposits that we use today

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The Ozone Layer

• The ozone layer formed when oxygen began to
  accumulate in the atmosphere
• Created a poisonous atmosphere where most of the
  organisms became extinct
• Those that survived became the anaerobic
  organisms that we know today or they evolved to
  use oxygen

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Endosymbiotic Theory

• Belief is that eukaryotes formed approx. 2
  billion years ago
• Prokaryotes moved into prokaryotic cells
• Created a symbiotic relationship
• One group was able to use oxygen to make ATP
• Mitochondria
• One group was able to use light to make sugars
• Chloroplasts

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Evidence of the Endosymbiotic Theory

• Membranes of mitochondria and chloroplasts are
  similar to that of free-living prokaryotes
• Mitochondria and chloroplasts have
• DNA similar to bacterial DNA
• Ribosomes similar to those of bacteria
• Reproduce by binary fission

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Sexual Reproduction

• The use of sexual reproduction by early organisms
  allowed evolution to occur at a much quicker rate
• More gene shuffling