History of Life on Earth

1
History of Life on Earth
2
Objectives

• Summarize how radioisotopes can be used to
  determine the age of the earth
• Compare two models that describe how the
  chemicals of life originated
• Describe how cellular organization might have
  begun

3
Age of the Earth

• Scientist believe that the earth originated 4.5
  billion years ago
• They speculate that it was a fiery ball of molten
  rock that cooled into a solid rock
• Water vapor in the atmosphere condensed to form
  the vast oceans of the planet
• Most scientists believe that life began in these
  oceans

4
Radiometric Dating

• Radiometric Dating A process of measuring the
  age of an object by determining its concentration
  of certain radioactive isotopes
• Scientists estimate the age of the earth through
  a process called radiometric dating

5
Law of Superposition

• A general law stating that in any sequence of
  sediments or rocks that has not been overturned,
  the youngest sediments or rocks are at the top of
  the sequence and the oldest are at the bottom

6
Half-Life

• The time it takes for one-half of a given amount
  of radioisotopes to decay
• By measuring the proportions of certain
  radioisotopes and their decay, scientists can
  compute how many half-lives have passed since a
  rock was formed

7
Formation of Chemical Life

• Scientist believe that life began as a random
  series of chemical and physical processes.
• It is thought that life began when non-living
  chemicals reacted chemically during the first
  billion years of the earth's history

8
Primordial Soup Model

• Scientists A.I. Oparin and J.B.S. Haldane
• Suggests that the ocean was filled with many
  different organic molecules
• Theorized that molecules spontaneously formed in
  chemical reactions powered by lightening,
  volcanoes and solar radiation

9
Urey-Miller Model

• 1953 Stanley Miller tests Primordial Soup theory
• He created complex organic molecules using the
  basic gases found in the earth's ocean

10
However...

• It was later determined that the earth did not
  posses an ozone layer.
• The ozone layer protects the earth from the sun's
  ultraviolet rays
• Without the layer of protection the rays would
  have destroyed any complex molecules created by
  the primordial soup model

11
Bubble Model

• If gases necessary for life to evolved had not
  existed in the atmosphere, where did they come
  from?
• 1986 Louis Lerman suggested that the gases were
  trapped in bubbles on the surface of the ocean

12
Bubble Model

• Simple organic molecules from number eruptions of
  undersea volcanoes were trapped in bubbles
• Inside the bubbles gases underwent chemical
  reactions due to the concentration of the
  chemicals

13
Bubble Model

• Bubbles rose to the surface and burst releasing
  the organic molecules into the air
• Up in the air, the organic molecules were exposed
  to ultraviolet radiation and lightening which
  provided energy for more reactions

14
Bubble Model

• More complex organic molecules formed by further
  reactions fell into the ocean with rain, starting
  another cycle