1. History of Life on Earth
BIOLOGY Chpt - 12
History of Life on Earth

2. The Theory of Spontaneous Generation
Before the microscope, it was commonly thought life arose from NON-LIFE - ABIOGENESIS
Flies came from rotting meat!
Bacteria came from rotting broth!
Francesco Redi - disproved flies came from rotting meat!
Louis Pasteur disproved bacteria spontaneously arose from broth!
BIOGENESIS- Life must arise from Life!!

3. HOW DID LIFE BEGIN? How did life form on Earth?
2-ways to approach this…..
Philosophy or Science

4. The AGE OF THE EARTH…………
Earth formed 4.5 billion years ago!
The Earth Began as a hot molten ball of lava..
3.9 billion years ago water vapor began to appear
3.5 billion years ago-life began!
From
Geology and
Archeology

5. A History in the Rock Oldest rocks - 3.9 billion years old!
They provide us with fossils, casts, imprints, and specimens in amber and ice
Most fossils occur in sedimentary rock!
Relative dating - layers closer to the surface are younger than those found in deeper layers!

6. From Chemistry-Radiometric Dating ...
TYPES
Carbon 14 –decays to Nitrogen.
half-life 5,730 years.
Potassium- decays to Argon then to calcium. half-life billion years
Uranium 238 –decays to lead. Dating….half life 704 million years
Radioisotopes-an unstable atom (extra neutrons)
Radioactive Decay the breakdown into smaller more stable atoms.
Half-life is the time needed for 1/2 of the substance to change!

7. GEOLOGIC TIME SCALE
The History of the Earth is divided into Four Eras
Precambrian-oldest fossils of cells / water invertebrates
Paleozoic -fish and plants appear
Mesozoic- age of the Reptiles
Cenozoic- Mammals

8. Plate Tectonics and. Continental Drift
The crust of the earth is floating on magma!
As the magma flows, the crust is broken apart and squeezed together!
These plates which hold the continents have moved location and thus affected life forms!
Where these plates meet cause earthquakes, and volcanic activity!

9. Mass Extinction….. 5 major mass extinctions
A time when suddenly large numbers of species become extinct !
Sudden Geological changes occur..
Asteroids
Volcanic eruptions

10. If Life comes from Life…. Where or How did the first life form arise
J.B. Haldane – and-
Alexander Oparin - hypothesized life began in the oceans from complex organic molecules!
Harold Urey- and Stanley Miller set up a test to see if the hypothesis had merit!

11. The Primordial Soup !
Stanley Miller’s experiment with the help of Harold Urey produced amino acids, sugars, and other organic compounds!
Similar processes have produced ATP- energy carrier, and nucleic acids- the building blocks for DNA!
BUT- If there was NO OZONE layer this process could not have happened!

12. The Bubble Model…
Louis Lerman – molecules for life formed within bubbles on the surface of the ocean.
gases trapped in ocean vents formed bubbles
methane and ammonia made amino acids released into atmosphere
UV rays forced further molecular change
these fell back into the ocean and repeated the cycle.

13. Proto cells… LIPIDS – (fats) form bubbles in water.
COACERVATES- amino acids and sugars form bubbles with cell membrane like structure.
MICROSPHERES – amino acid chains form bubbles
Scientists Cech and Altman showed that RNA can reproduce itself and can modify its structure over time.

14. The Evolution of PROKARYOTES
The oldest known fossils are the PROKARYOTES.
CYANOBACTERIA- blue green algae produced the OXYGEN in air !!
Ancient prokaryotes are called ARCHAEBACTRIA.

15. The first EUKARYOTE CELLS
1.5 Billion years ago…
first fossils of Eukaryotes!
Eukaryotes have organelles within..(Nucleus and others)
Archaebacteria
Cyanobacteria- developed into Chloroplasts and Mitochondria
Endosymbiosis occurred..
forming first Eukaryote cell

16. The ENDOSYMBIOTANT HYPOTHESIS
Evidence-
Mitochondria –same size as bacteria
Chloroplasts and Mitochondria have membranes like bacteria
Both have there own DNA
Both –have ribosomes like bacteria
Both Reproduce like bacteria
Lynn Marguli –
Proposed prokaryote cells engulfed smaller cells and formed a symbiotic relationship – of mutualism…..
where both benefit!

17. Multicellularity Protists – Primative unicellular
and multicellular organisms
Multicellularity
Unicellular organisms unite to form
multi-cellular
organisms
Specialization – cells become specialized for a particular function

18. OZONE LAYER As ozone formed , it allowed life to move onto the land….
First Fungi as it can absorb minerals
Plants need the minerals to carry on photosynthesis…they came next..
MYCORRHIZAE- fungi and plants in a symbiotic relationship of Mutualism!

19. Invertebrates….arrive
Arthropods followed plants
insects – spiders- centipedes-etc
Vertebrates…
..fish were evolving as the arthropods developed on land..
. Amphibians evolved from fish
.Reptiles developed the egg
.Birds developed from reptiles
.Reptiles gave rise to the mammals