1. The History of Life & The Theory of Evolution
J. Quigley
2008

2. Early History of Earth
Early earth was inhospitable: very hot with volcanoes spewing lava and gases
The gases from the volcanoes helped create the ancient atmosphere which probably had little oxygen, a lot of water vapor, carbon dioxide and nitrogen.

3. Early Earth
Around 3.9 billion years ago Earth might have cooled enough for water in the atmosphere to condense.
The condensing water might have led to millions of years of rainstorms and lightning creating the oceans
Some scientists believe between 3.9 and 3.5 billion years ago, the first organisms appeared in the ocean

4. History in Rocks: Scientists can’t be certain how earth formed, but rocks help create hypotheses
Fossils are clues to the past.
A fossil is evidence of an organism that lived long ago.
Fossils can form many different ways

5. Types of fossils
Trace Fossils- a marking left by an animal like a footprint, trail or burrow.
Cast Fossils- when minerals in rocks fill the space left by an organism, they make a replica of the organism

6. Types of fossils
Imprint Fossils- thin objects such as a leaf fall into sediment, they leave an imprint when the sediment hardens into rock.
Mold Fossils- when an organism is buried in the sediment and then decays leaving an empty space

7. Types of fossils
Petrified Fossils- Minerals sometimes penetrate and replace the hard parts of an organism, producing copies of them
Amber Preserved and Frozen Fossils- At times an entire organism is trapped in ice or tree sap that hardens into amber

8. Paleontologists- Detectives of the past
Studying fossils is like solving a mystery.
Paleontologists study ancient life and use fossils to try to understand the events that happened long ago.
Fossils can explain where the organism lived, what it ate, size, and even sometimes behaviors.
Fossils can also help explain ancient climate and geography

9. Sedimentary Rock
For a fossil to form, organisms usually have to be buried in a small particles of mud, sand or clay soon after they die. These particles compress over time and harden into sedimentary rock (Look at page 381)

10. Dating Fossils: (not “dating” but how old are they) ha-ha!
Relative Dating- Fossils that are found deeper in the ground are older than ones found closer to the surface. This is the principal of geological law. Layering of rocks tells scientists which fossils are older than others
Radiometric Dating- Scientists use isotopes in the fossils to determine the exact age of the fossil. Isotopes “decay” at specific a speed, so they can look at the isotopes and determine the age of something.

11. A Trip Through Time
The geologic time scale is divided into four eras: Precambrian, Paleozoic, Mesozoic and Cenozoic.
Each era is divided into smaller amounts of time called periods
Time scale is distinguished by the organisms that lived during the time period.

12. Geologic Time Scale

13. Geologic Time Scale
The fossil record indicates that there were several occurrences of mass extinction that fall between the time divisions
Mass extinction is an event where entire groups of organisms disappear from the fossil record almost at once
The geologic time scale begins with the formation of earth about 4.6 billion years ago

14. Pangaea
About 245 million years ago the continents where joined in a landmass called Pangaea
About 66 million years ago most of the continents had moved away from each other and look like they do now

15. The Origin of Life
Modern Ideas
Biologists have accepted the concept of BIOGENESIS for more than 100 years…but biogenesis doesn’t answer the question “How did life begin on earth?”…no one will ever know for sure. (biogenesis means cells come from other cells)
Early Ideas Spontaneous generation: the idea that non-living material can produce life.
Cells only can come from other cells, so this idea was disproved.

16. Modern Ideas
Scientists believe two things needed to happen before life could begin
Organic molecules (contain carbon) must have formed
The organic molecules formed carbohydrates, fats, proteins and nucleic acids

17. The next step proposed by scientists was the molecules would make complex organic compounds called protocells.
Protocells: a large ordered structure, enclosed by a membrane that carries out some of life’s activities such as growth and division

18. True Cells
The 1st life forms may have been prokaryotes that evolved from a protocell.
Because the atmosphere didn’t have much oxygen, it is believed that the 1st organisms were anaerobic (don’t need oxygen)
The prokaryotes probably ate the complex molecules that were floating in the ocean (heterotrophs: do not make their own food)

19. Archeabacteria These first cells are thought to be Archeabacteria,
these prokaryotes still survive today in the
Earth’s harshest environments
(volcanoes, deep sea vents, hot springs, salt beds)

20. First True Cells: Prokaryotes
Photosynthesizing (make nutrients using energy from the sun) prokaryotes were probably the next organism to evolve.
Photosynthesis produces oxygen
Because of the extra oxygen, organisms started to become aerobic (using oxygen)

21. Eukaryotes: Endosymbiont Theory
Prokaryote ingests some aerobic bacteria. Aerobic bacteria is protected and prokaryote gets energy
Over time the aerobes become mitochondria, no longer able to live on their own.
This is an animal cell

22. Endosymbiont Theory
Some primitive prokaryotes ingested cyanobacteria, which contain photosynthetic pigments
The cyanobacteria become chloroplasts and no longer can live on their own
This is a plant cell