1. Chapter 12 History of Life

2. 12-1 How Did Life Begin How old is the Earth? 4.5 to Billion Year Old!
How do we know?

3. Radiometric Dating
Calculating the age of an object by measuring the proportions of the radioactive isotopes of certain elements
Radioisotopes are unstable elements
They decay, or break apart

4. We measure decay using the half-life of the element
Half-life means how long it takes for half the atoms of a given radioisotope to decay
Different half-life # for different elements

5. Life From ?? Life on planet Earth came from two possible sources.
Most likely is Spontaneous Origin, life developing from organic molecules reacting with the environment
Where do we get organic molecules?

6. Deep Sea Hydrothermal Vents
Extraterrestrial Seeding
Frozen Ocean Theory

7. Conditions of Early Earth

8. THE EARLY ATMOSPHERE Possible gasses: H2O, NH3, CH4, H2, CO2.
Ammonia would have broken down:
2NH3 into N2 + 3H2 (escaped to space)
Final content was probably H2O vapor, CO2 and CO, N2 (80%).
NO OXYGEN

9. NO ENZYMES WERE PRESENT
REQUIREMENTS FOR LIFE
Lack of oxygen (reducing atmosphere).
Appropriate chemicals (water, organic and inorganic molecules)
Sources of energy (U.V., heat, lightning)
Great amounts of time
NO ENZYMES WERE PRESENT
REACTIONS WERE SLOW

10. Oparin and Haldane 1920s
Hypothesized steps of chemical evolution from primitive earth conditions.
Led to the Primordial Soup Model

11. Miller and Urey, 1953 Tested Oparin and Haldane’s hypothesis.
Experiment - to duplicate primitive earth conditions in the lab.

13. Results
Organic monomers formed including Amino Acids.

14. Problems With The Model
No ozone to protect the gases in the atmosphere
UV radiation would have destroyed ammonia and methane

15. Bubble Model
Louis Lerman suggested that the key process to form organic chemicals occurred at the ocean’s surface

16. What About Genetic Information?

17. Genetic Information DNA  RNA  Protein Too complex for early life.
Other forms of genetic information?

18. RNA Hypothesis
RNA as early genetic information.

19. Rationale RNA polymerizes easily. RNA can replicate itself.
RNA can catalyze reactions including protein synthesis.

20. What About Cell Membranes?
Short chains of amino acids can lead to microspheres

21. Coacervates
Colloidal droplets of proteins, nucleic acids and sugars surround by a water shell.
Will form spontaneously from abiotically produced organic compounds.

22. 12-2 Development of Life Oldest fossils are 3.5 Billion Years Old
They are prokaryotes
First prokaryotes were heterotrphs then autotrophs
Cyanobacteria were among the first photosynthetic bacteria
Responsible for free oxygen in the atmosphere

23. Eubacteria are prokaryotes that contain peptidoglycan
Archeabacteria are prokaryotes that do not contain peptidoglycan
Evidence indicates that archeabacteria were the 1st group to evolve

24. 1st Eukaryotes Appear about 1.5 Billion Years Ago
Mitochondria and Chloroplast appearance explained by endosymbiosis
These organelles are descended from aerobic, symbiotic eubacteria
Both organelles have their own DNA

25. Multicellular Forms of Life
Have developed many times
Life grouped into 6 Kingdoms
Eubacteria and Archeabacteria are single celled
Fungi, Plants, Protists, and Animals have multicellular organisms

26. Cambrian Explosion
When the most of the current body plans 1st appear in the fossil record
Most famous fossil find from this time period was the Burgess Shale

27. Mass Extinctions
Impact life because it reduces the amount of competition for resources
Allows for adaptive radiation to occur
Almost every time period has one!

28. 12-3 Progression of Life
Once the ozone layer formed, life could invade the land
Ozone began to form around 2.5 BYA
Is formed when oxygen gas (O2) becomes O3 from the radiation of the sun

29. 1st multicellular land organisms were plants and fungi (Around 430 MYA)
Created a mutualistic realationship
Means both benefit
Called mycorrhizae

30. Arthropods were the first animals to invade land (After the plants and fungi)
Arthropods have a hard exoskeleton and jointed limbs
Examples include lobsters, crabs, insects, arachnids, scorpions

31. Vertebrates followed arthropods
Vertebrates have a backbone
First ones were small, jawless fish in the oceans
Then came the jawed fishes

32. Amphibians were the 1st land vertebrates
Could breath air
Had better adaptations for thriving on land than fish

33. Reptiles evolved from amphibians
Even more adapted to life on land
Had water tight skin, and shelled eggs

34. Mammals and Birds evolved from reptiles
Better adapted to the changes in the climate at the end of the Cretaceous

35. Time Periods in Order Cambrian (Oldest) Ordovician Silurian Devonian
Carboniferous
Permian

36. Triassic
Jurassic
Cretaceous
Tertiary
Quaternary (Present)