1. HISTORY OF LIFE
Chapter 14

2. The Record of Life
Ch. 14, Sec 1

3. Early History of Earth
5 billion years ago our solar system was formed as a swirling mass of gas and dust
Gravity pulled this material together to form the sun
Remaining gas and debris circled the newly formed sun
Collisions between the space debris created the planets

4. Earth formed about 4.6 billion years ago, dated by studying the layers of rock that make up the planet
Young Earth was hot, there was no atmosphere to block UV rays from the sun
No oxygen to breathe
A lot of carbon dioxide and water

5. Life originated in Earth’s oceans 3.9-3.4 billion years ago
Early life forms would have been very similar to bacteria

6. History in Rocks
Rocks provide information about Earth’s history including the history of life on Earth
Paleontologists study ancient life and fossils

7. Fossils are found in sedimentary rock
Organism gets buried in mud, sand, or clay after they die
More sediment gets layered over the organism, over time the minerals in the sediment replace the minerals in the skeleton

9. Dating Fossils
Relative Dating = layers of rocks have different ages, the “youngest” layers on top; older fossils found in older layers of rock
Radiometric Dating = atoms in the fossil break down at a certain rate, age of the fossil depends on the ratio of atoms to broken down atoms

10. Geologic Timescale
Begins with the formation of Earth and goes through present time
Scale is divided up by the kinds of organisms that lived during that time

11. Layers of rock match up with the Geological Timescale

12. Organization of the GTS
Broken down into 4 Eras, each era is further broken down into Periods
The eras and periods are characterized by specific events and specific organisms
All eras are NOT the same length of time!
Mass Extinction = many organisms disappear from the GTS almost all at once

13. 4 Eras 1. Precambrian Era 4.6 BYA - 580 MYA (4,020,000,000 years long)
Beginning of the GTS, longest era 87% of Earth’s history
Oldest rocks are from the Precambrian, oldest fossils too
First organisms were single celled

14. 2. Paleozoic Era 580 MYA – 248 MYA (332,000,000 years long)
Cambrian Explosion occurred during the Cambrian Period
Enormous increased in diversity of life in oceans
Organisms with backbones emerged
Mass extinction occurred at the end of the Paleozoic Era killing off 90% marine life, 70% land life

15. 3. Mesozoic Era
248 MYA -65 MYA (183,000,000 years long)
Era of the dinosaur
Dinosaurs died out during another mass extinction making room for mammals
Meteor crash could have caused the mass extinction

16. 4. Cenozoic Era
Began 65 million years ago, continues today
Increased diversity in mammalian life
Modern humans appeared 200,000 years ago

17. As you move towards the bottom of the rock layers, you move back on the Geological Timescale
Similar fossils found on different continents because at several times in Earth’s history the continents were connected

19. Pangea existed 250 million years ago
Plate Tectonics = the surface of Earth is made up of plates that drift on top of a molten layer of rock

21. The Origin of Life
Ch. 14, Sec. 2

22. Spontaneous Generation
Pre-17th century it was believed that living things arose from nonliving things through a process called Spontaneous Generation

23. 6th century BC: Greek philosophers propose life arose when sunlight was shined onto mud
Why?

24. 1600’s: It was believed that mice appeared from rotten grain
Why?

25. Francesco Redi ( )
Mid-17th century people believed flies were spontaneously generated from rotting meat
Redi was a scientist who noticed a life stage to the flies on the rotten meat
1. Maggots
2. Pupa
3. Flies
He observed that the maggots appeared where flies had landed first

27. Redi predicted that if the meat could be kept away from the flies, then there would be no maggots on the meat
He did not believe that flies spontaneously generated from meat!!!
So he set up his experiment…

28. Control Group = uncovered jar of meat, flies layed eggs, which hatched into maggots, which turned into more flies
Experimental Group = covered jars of meat, flies have no chance to lay eggs, new flies do not appear

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30. Louis Pasteur ( )
Finally disproved spontaneous generation once and for all! 200 years after Redi’s experiment
Pasteur set up an experiment where boiled broth was exposed to air, but microorganisms couldn’t fall in

31. By the 1800’s scientists understood (thanks to the microscope invented a century ago) that microorganisms (bacteria & viruses) caused people to get sick
But….

32. Some scientists still believed that bacteria and viruses spontaneously generated from the air
Pasteur proved them wrong with his experiment

33. Boiled broth was exposed to air in a specially shaped flask over a period of time but nothing grew
Once the neck was broken off bacteria grew in the broth
Bacteria did not spontaneously grow from the air!!!

34. Thanks to Pasteur….
Biogenesis = living organisms come from other living organisms

35. Modern Experiments on Origins
All elements found in organic compounds needed to form biomolecules existed on Earth since its formation
Early atmosphere contained Ammonia (NH3), Hydrogen Gas (H2), Water Vapor (H2O), Methane (CH4)

36. Under high temperature the gases might have formed simple organic compounds (contains Carbon) like amino acids
When Earth began to cool the organic compounds would have condensed with the water vapor and collected in lakes and seas

37. Stanley Miller & Harold Urey (1953)
Recreated the conditions of early Earth in the lab on a smaller scale
Included chemicals present at the time and an energy source similar to what as present at the time
Able to generate amino acids (biomolecule)

39. Alternative Hypotheses
1. Life (biomolecules) emerged in ice (Stanley Miller)
Within ice there are chemicals to create biomolecules & microscopic pockets of water

40. Water freezes forcing the chemicals to be close together which increases the chances of chemical reactions occurring
When the ice melts the biomolecules generated are released into oceans

41. 2. Life (biomolecules) emerged in deep sea vents
Vents provide the heat & chemicals that could cause chemical reactions to generate biomolecules

42. Formation of Protocells
Protocell = Heating the amino acids can cause them to take on some life activities like growth and division

43. First True Cells
No direct evidence of the first cells, scientist can only analyze data that we collect now
Early Earth had little oxygen, oldest fossils thought to be cells resemble the size & shape of some living prokaryotes, the first cells had organic molecules to eat

44. Therefore….
The first cells were anaerobic, heterotrophic prokaryotes
Anaerobic = respiration that doesn’t require oxygen
Heterotrophic = needs to eat other things in order to get the organic molecules needed for life

45. Next evolved…
Autotrophs = make their own food
Early autotrophs similar to present day Archaebacteria
Archaea = prokaryote organisms that thrive under harsh conditions, make food through chemosynthesis
Chemosynthesis = CO2 is the carbon source, energy comes from the use of inorganic chemicals

47. Next evolved…
Photosynthetic prokaryotes
Autotrophs now able to use sunlight energy to make food
Created oxygen for the atmosphere which allowed for an increase in diversity of life because now there was an ozone layer (provides protection from UV light)

48. Endosymbiotic Theory Eukaryotic cells evolved from Prokaryotic cells
Symbiosis = close, long term relationship between species
An ancient prokaryote engulfed another prokaryote and instead of digesting it they lived together

49. This explains why mitochondria has its own DNA and a double membrane

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