BIOL 1202 Lecture : Biology 1202 Lecture 2
Biology 1202 Lecture 2
Chapter 25
o How did life begin?
o A few centuries ago …
▪ People thought that new living things appeared all the time
▪ 1609 “ There is a tree… frequently observed in Scotland. From
this tree leaves are falling; upon one side they strike the water
and slowly turn into fishes, upon the other side they strike the
land and turn into birds.
o Spontaneous Generation Refuted
▪ Mid 1800’s Louis Pasteur (broth in flask is boiled to kill
preexisting microorganisms).
▪ As broth cools, condensing water collects, sealing the mouth of
the flask
▪ If neck is later broken off, outside air can carry microorganisms
into broth
o Somehow, life spontaneously generated on the earth, we don’t know why.
o Conditions on early earth
▪ Atmosphere:
• Carbion dioxide, methane, ammonia, hydrogen,
nitrogen, HCl, HS, water vapor
• No free oxygen
• Frequent storms with lots of lightning
• Frequent volcanic eruptions
• Frequent meteor impacts
• UV light from the sun
• No Ozone layer
o Earth Before Life Arose
▪ Earth is about 4.6 billion years old
• Radiometric dating of meteorites and moon rocks
▪ Life arose about 3.8 billion years ago
• Chemical traces in rocks are verification
• Fossil bacteria in rocks 3.5 BY
• No Spontaneous generation now, but must have
happened then
o Rate of Decay of 40K to 40Ar
▪ Potassium 40 naturally decays to argon 40
o The Experiment of Miller and Urey-tried to replicate early conditions on
earth to produce life
o Used purified water, gases from primeval atmosphere
o Organic molecules appear after only a few days
▪ Ex. Amino acids
o How To Assemble a Living thing
o Accumulation of Organic Molecules (hypothesis)
