1. History of Life on Earth
Ch. 12
Biology
Ms. Haut

2. How was the Earth Formed?

3. According to the BIG BANG, the universe was created sometime between 10 billion and 20 billion years ago from a cosmic explosion that hurled matter and in all directions.

6. The Origin of Life Began in Chemistry
Spontaneous origin—molecules of nonliving matter reacted chemically to form many different simple, organic molecules

7. Early Earth: Primordial Soup
Ancient Atmospheric Gases—H2O, CH4 (methane), NH2 (ammonia)
Additional gases (common emissions of modern volcanoes)—CO, CO2, N2, H2O vapor, H2S/FeS, HCN, H2
Meteor bombardment
Lightning, heat, and UV radiation served as energy sources

8. Can organic compounds be generated under conditions similar to those that existed on primeval earth?
Stanley Miller and Harold Urey (1950s) designed an experiment that demonstrated the possibility that organic compounds could be generated.

9. Early atmosphere of gases: methane, ammonia, hydrogen, and water vapor
Electrical sparks simulate lightning
Condenser cools gases in a “rain”; compounds collect in an “ocean”
Found pyrimidines, purines, and amino acids

11. Organic Chemicals Became Complex
Many hypothesize that inorganic molecules formed RNA nucleotides
Short chains of RNA nucleotides may have been the first self-replicating information-storage molecule (acting like enzymes)
Could have also catalyzed the assembly of the first proteins

12. First Genetic Material and Enzymes may both have been RNA

13. Microspheres May Have Led to Cells
Short chains of amino acids tend to gather into tiny vesicles called microspheres
Other molecules of different types formed vesicles called coacervates

15. Coacervates of lipid
microsphere

16. Prokaryotes are the Oldest Organisms
Microfossils

18. Archaebacteria Thought to be closely related to the first bacteria
Exist in harsh conditions (similar to early Earth)
Extreme heat
Lack of oxygen

19. Photosynthetic Prokaryotes
Cyanobacteria—among the first to appear
Produced and released oxygen into the oceans
Changed the earth’s atmosphere

20. Modern stromatolites in Shark Bay, Australia
Mats of photosynthetic organisms – cyanobacteria, algae and phototrophs

21. Modern Microbialite domes similar to ancient reef structures

22. First Eukaryotes: Endosymbiosis
~1.5 billion years ago
Protists
Single cells; some cells sharing a symbiotic relationship with others
Today’s eukaryotes contain mitochondria and chloroplasts
Because these organelles have their own DNA, they may be descendants of symbiotic, aerobic eubacteria and cyanobacteria

23. First Multicellular Organisms on Land
Plants evolved from photosynthetic protists paired up with fungi
Plants could harvest sunlight to make food / fungi could harvest minerals from bare rock
Mycorrhizae 

24. Life Invaded Land
With the development of photosynthetic bacteria came the development of an atmosphere containing oxygen
UV radiation from the sun reacted with the oxygen to form the ozone layer around the earth
Protected organisms from destructive radiation, allowing them to survive on the land

25. Arthropods
~100 million years after plants/fungi covered the earth, animals could survive on land
Arthropods are believed to be the first
Have hard outer skeleton and jointed limbs
Lobsters, insects, crabs, spiders
Specific traits allowed certain animals to survive and reproduce and pass on their genes
Eryon arctiformis

26. Vertebrates Animals with backbones (endoskeletons)
The first were jawless fishes (500 mya)
430 mya jawed fishes

27. Vertebrates Amphibians –first vertebrates on land
Had lungs, allowing them to absorb oxygen from the air
Limbs believed to be derived from bones if fish fins
Strong, flexible internal skeleton allowed animals to be much larger than insects
Plethodon glutinosus: Slimy Salamander
Lysorophid amphibian

28. Vertebrates Reptiles –350 mya
Watertight skin protected from dessication
Lay eggs with shells on land
Better adapted to dry climate
Iguana

29. Vertebrates
Birds
Winged animals
Can fly
Hollow skeleton

30. Evolution of Organisms
Extinctions –death of a species
opens up niches for other species to become more abundant
Continental drift—movement of Earth’s land masses over geologic time
Contributed to geographic distribution of some species
Marsupials in Australia and South America