1. Chapter 12 History of Life

2. Fossil Record Fossils – preserved form of ancient life
- can be found in ancient rocks, petrified tree sap, peat bogs, tar pits, and polar glaciers
Fossil record – grouping of similar organisms and arranging them in order in which they lived – oldest to most recent
- provides evidence about history of life on Earth and how different groups changed over time

3. Fossil Record Paleontologists are scientists who study fossils
- compare anatomical similarities to present day living organisms
- try to sequence the age based on location in the rock layers
Its believed that 99% of all species have become extinct or died out over course of Earth’s history

4. Fossil Formation Most fossils form in sedimentary rock
conditions deteriorate other rock layers into small particles that then carried to other locations and settle into sediment layers
Sediments are compressed together preserving intact organisms within layers

5. Dating Fossils
Two ways of determining age: 1. Relative dating – determines age of fossil by comparison of its placement with fossils in other rock layers. - rock layers form in order by age where oldest is at the bottom and youngest near the surface 2. Radioactive dating – uses the half life of radioactive elements to predict absolute age - elements decay at a certain rate; when half of the sample remains, that is the half life Ex: carbon 14(radioactive isotope)

6. Geologic Time Used to represent evolutionary time
Combines worldwide index fossils; and rock layers, relative age of rock layers
Radioactive dating has sequence ages that vary in millions of years
Segments have 3 major divisions:
1. Precambrian time
2. Eras – Paleozoic, Mesozoic, and Cenozoic
3. Periods – Mesozoic Era
- Triassic
- Jurassic
- Cretaceous

8. Earth’s Early History
Earth’s origin is believed to be 4.6 billion years old
Conditions and contents of chemicals were quite different from today
Ex: atmosphere was possibly made up of hydrogen cyanide, CO2, CO, H2SO3, Nitrogen, and water
Volcanic eruptions, comet and asteroid collisions, and lack of oceans

9. First Organic Molecules
1950’s scientists Stanley Miller and Harold Urey ran experiments to find out if organic molecules could have formed under harsh conditions of the infant planet Earth
- filled flask with hydrogen, methane, ammonia and water to simulate the atmosphere and passed electric current through the mixture
-over days they produced several amino acids

10. Life’s Origin
Under certain conditions large organic molecules can form tiny bubbles called proteinoid microspheres
- not cells but resemble living systems
- membranes, stores and releases energy
- evolved to modern form of cell
RNA may have formed before DNA and given rise to the evolution of DNA

11. Free Oxygen
Microfossils resembled the first single celled prokaryotes that changed to modern bacteria
They evolved without oxygen and over time became photosynthetic
Oxygen combined with iron in the oceans making them orange
Increase in oxygen served as pollutant to the Earth and may be to blame for extinction of some life forms; while others evolved

12. First Eukaryotes
Possible origins of a nucleus containing cell began 2 billion years ago
The Endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms
- mitochondria and chloroplast make the main connection to theory
- both have DNA
- both have ribosomes
- both can reproduce by binary fission

13. Patterns of Evolution
Macroevolution – large scale evolutionary patterns and processes, beyond a single species, that occur over long periods of time
Six patterns of macroevolution are:
1. Extinction
2. Adaptive radiation
3. Convergent evolution
4. Coevolution
5. Punctuated equilibrium
6. changes in developmental genes

14. Extinction What are the events that led to extinction of species?
What separates mass extinctions from extinction itself?
Competition for resources and environmental change, lack of adaptations ( or Natural selection itself) can explain some extinctions.
Mass extinctions were usually occurred because food webs collapsed, energy flow was disrupted, and basically the environment is collapsing around the organisms.
Ex: Massive asteroids collisions, shifting continents, changes in sea level

15. Adaptive Radiation
Evolution of many diversely adapted species from a common ancestor after being introduced into new environmental opportunities and challenges
Changes in environment can cause the progression and divergence toward dominant species in the ecosystem;
Extinction clears the way other species to become more prominent and diverge

16. Convergent Evolution
Process where unrelated organisms come to resemble one another
- caused with different species undergo adaptive radiation to similar environmental conditions
- organisms have different ancestral species but same demands of the environment
- Analogous structures - structures of the body between two species have similar appearance and function, but have different parts and different evolutionary history
Ex: bee wings vs. hummingbird wings

17. Coevolution
Process where two species evolve in response to changes in each other over time
- usually two closely connected species that have frequent ecological interactions
Ex: flowering plants and their pollinators

18. Punctuated Equilibrium
Punctuated equilibrium – episodes in fossil record where a new species suddenly appeared, persisted unchanged, and then disappear
- Time period of the fossil record skews the perception of changes that occurred making them unnoticeable
- long stable periods interrupted by rapid change

19. Developmental Genes
Controlling gene expression by turning genes “on or off” can dramatically effect the growth and differentiation of embryonic cells
Ex: hox genes control orientation of body parts
- small changes in control genes can have large impact on adult organisms
- sheds new light on evolutionary transformation of species