Download Theory =

History of life notes
Early Earth
4.6 bya (billion years after)
- VERY (colliding meteorites, erupting volcanoes)
- Atmosphere was mostly nitrogen, carbon dioxide, water vapor, methane,
ammonia but NO OXYGEN!!!!!
4.4 bya
- Earth cools
- water vapor condenses into rain creates oceans (where the first life will form)
Evidence that we do have!
Fossils = evidence of an organism that lived long ago and show the great diversity of life
(Examples:
A person who studies fossils is called a paleontologist (just like Ross on Friends!)
How is a fossil made?
- After an organism is buried, the sand and clay around it harden to form
sedimentary rock. Then erosion brings the fossil to the surface
Dating Fossils
1. Relative Dating- older rocks/fossils are on the bottom, younger ones are on top
2. Absolute Dating (also called radiometric dating)- measures the amount of
radioactive substance left in the rock or organism and determines its actual age
By examining rock layers and dating the fossils, scientists have been able to put together
a chronology, or calendar of Earth’s history called the Geologic Time Scale (see left
page)
Origin of Life
Cell Theory
1. all living things are made of cells
2. cells are basic unit of structure & function
3. All cells come from pre-existing cells.
What is the big question this theory raises?
1. Where did the first cell come from?
2. What can be observed now if it happened so long ago?
- The initial belief was that life was created through spontaneous generation
(abiogenesis).
Example: a piece if decaying meat produces maggots (baby flies)
Disproving Spontaneous Generation
1.
Francesco Redi was the first to disprove spontaneous generation in the 1600s.
History of life notes
Although Redi was able to disprove that large organisms did not simply appear,
many scientists thought that microorganisms (bacteria) were so numerous and
widespread that they must arise spontaneously- probably from a vital force in the air.
2. Louis Pasteur in the mid 1800’s designed an experiment that disproved the
spontaneous generation of microorganisms
From this time on BIOGENESIS, the idea life comes from life holds true.
(Ex. Humans give birth to humans, mice to mice, etc.)
But…. How did the very first life form that start this chain reaction?!!!
The current theory is that life began in the oceans.
Oparin’s hypothesis: Energy from the sun and lightning triggered chemical reactions
with the vapors that were present in the early atmosphere to produce small, organic
molecules. Then, the rain washed the molecules into the ocean to create what is called
the primordial soup. (place of the origin of life).
PROOF??
1953- Stanley Miller and Harold Urey tested the hypothesis by simulating the conditions
History of life notes
of early Earth in a lab.
Simple Molecules to Complex molecules?
- experiments were done to prove that simple molecules like amino acids when
heated without oxygen link up to form proteins (complex molecules)
Complex Molecules to Cells?
- Sidney Fox showed how amino acid chains will form protocells
Evolution of Cells
1st cells = prokaryotic, anaerobic and heterotrophic (does not make own food)
2nd cells = autotrophic prokaryotes (makes own food)
3rd cells = photosynthesizing prokaryotes
First organisms were prokaryotes
2 types
– Archaebacteria – bacteria that live in harsh environments, and more
closely related to early prokaryotes
– EubacteriaEndosymbiotic theory
Pre-eukaryotic bacteria engulfed another
– (similar to mitochondria or chloroplast)
History of life notes
Eukaryotic organisms formed much __________________ than prokaryotes
Summary