1. The History of Life
Chapter 12

2. The Fossil Record Fossil Forming Most fossils form in sedimentary rock
Perminerilization
Natural Casts
Trace Fossils
Amber preserved fossils
Preserved remains
Most fossils form in sedimentary rock
Preminerilization – minerals carried by water are deposited around a solid structure – most common
Natural Casts – flowing water removes all the original bone or tissue leaving an impression in the sediment
Trace fossils- record the activity of an organism; nests, burrows, imprints, and footprints
Amber preserved fossils – organisms trapped in tree resin
Preserved remains – entire organism trapped in ice or volcanic ash or immersed in bogs
Fossil Formation
Must be buried or encased in some type of material (sand, deiment, mud, tar) very soon after death
Groundwater trickles into tiny pores and spaced in plants and bone
Excess mineral in the water are depostied on the remaining cells or tissues
Many layers are deposited and left behind
Resulting minerals are the same shape as the organism

3. The Fossil Record

4. The Fossil Record Relative Dating
Estimates the time an organism was alive based upon it’s placement in rock layers
Allows for inferences of species origin
Does not provide actual age dating of fossil

5. The Fossil Record Radiometric Dating Half life
Estimates actual or absolute age
Calculation of the age of a sample based upon the amount of remaining radioactive isotopes
Half life
The amount of time it takes for half of the iostopes in a sample to decay into another element
Different items have different half lives
Isotopes are atoms with differing numbers of neutrons
Carbon has three isotopes – C12, C13, and C14 – 98% are C12
Carbon 14 has a half life of 5730 years

6. The Fossil Record Carbon-14 Dating Good for recent remains
Carbon-14-taken up by organisms while they are alive
C-14 begins to break down when organism dies
Researchers compare the amount of Carbon-14 to Carbon-12 or Nitrogen-14
The larger the ratio of C-14 to C-12 (or N-14), the older the organism
Carbon has three isotopes – C12, C13, and C14 – 98% are C12
Carbon 14 has a half life of 5730 years – after 5730 years half the C14 in a fossil will be gone

7. The Geologic Time Scale
Index Fossils
Easily recognized and the species must have existed for a short period, but have a wide geographic range
It will only be found in a few layers, but they will be specific and in different locations
Trilobite

8. Geologic Time Scale
Evolutionary time is represented by the Geologic Time Scale
This orders rock by age
Divided into units based on order rocks and fossils were formed
Geologic Time Scale was developed by comparing index fossils throughout the world
Eras
Periods
Epochs
Time did not begin until the Precambrian period – covers about 88% of the Earth’s history

9. Geologic Time Scale
Time between the Precambrian period and now is divided by eras
Paleozoic
Mesozoic
Cenozoic
These divisions are defined somewhat by the organisms present
Paleozoic – 300 million years – life begins – ancient life
Mesozoic – 180 million years – Dinosaurs – middle life
Cenozoic – last 65 million years – age of mammals – recent life

10. Geologic Time Scale
To further define time, eras are divided into periods
The Cambrian period is important to biology due to the huge explosion of organisms
Epochs
Smallest unit of time; several million years

11. Origin of Life Earth is about 4.6 billion year old
How did the earth get here?
Formed by a condensing nebula
Material pulled together
Collisions caused the formation of planets

12. Origin of Life Earth was very hot, violent first 700 million years
Many objects struck Earth releasing heat – kept Earth in a molten state
Objects eventually separated into layers
Hydrogen, carbon monoxide, water vapor, methane, and carbon dioxide released
Oxygen not released until about 2 billion years ago

13. Origin of Life Miller-Urey Experiment
Lightning strikes caused inorganic molecules to form organic molecules
Electricity applied to these inorganic molecules led to the production of amino acids
Miller and Urey simulated the chemical nature in a lab of early earth
They filled a flask with hydrogen, methane, amonia and water to represent the atomosphere
They also made sure no microorganisms were present in the system
They then passed an electric spark to simulate lightining
The results showed that several amino acids began to form over several days
This suggested that the building blocks for life may have arisen from simpler compounds present on primitive earth

14. Origin of Life Meteorite Hypothesis
Amino acids have been found in meteorites
Suggests that amino acids could have been present when Earth formed

15. Origin of Life Iron Sulfide Hypothesis
Iron sulfide from deep sea vents form chimneys
Compartments in these chimneys acted as pockets for biological molecules
The walls of these compartments acted as the first cell membranes

16. Origin of Life Lipid Membrane Hypothesis
Lipids tend to form spheres – liposomes
These spheres could enclose organic molecules
Give rise to cells

17. Origin of Life RNA – Early Genetic Material
Ribozymes – RNA molecules that can catalyze chemical reactions
Can make enzymes that would cut itself, copy itself, and make more of itself
Short chains of RNA can form from inorganic molecules

18. Early Single-Celled Organisms
Early microbes changed the Earth
Deposited minerals, gave off oxygen
Cyanobacteria – bacteria that carry out photosynthesis
Stromatolites – colonies of cyanobacteria
Release of oxygen allowed for aerobic organisms
If doing photosynthesis, then giving off oxygen

19. Early Single-Celled Organisms
Early prokaryotes are considered the ancestors of eukaryotes
Early on some smaller prokaryotes began to enter into other prokaryotes
Endosymbiotic Theory
Eukaryotic cells arose from living communities formed by prokaryotic cells
These prokaryotes did not infect the host and the host did not ingest the ones that entered.
The prokaryotes that entered began living in the other cells. This resulted in a symbiotic relationship (each one helping the other)
One group could use oxygen to generate ATP – these became mitochondria
Another groups carried out photosynthesis – these became chloroplasts in plants
This idea came about when microscopes revealed that membranes of mitochondria resembled plasma membranes of free living prokaryotes

20. Eukaryotic Origins Evidence of the Endosymbiotic Theory
Mitochondria and chloroplasts:
Contain DNA similar to bacterial DNA
Have ribosomes whose structure and size closely resemble bacterial ribosome
Reproduce by binary fission
These three key pieces of evidence are what give credence to the idea that eukaryotes formed from prokaryotes

21. Reproduction and Multicellularity
After arrival, eukaryotes reproduced sexually
This increased the speed of evolution
Sexual reproduction allowed for shuffling of genes
Offspring never resembled their parents exactly
This increased the gene combinations – So?
Sped up because prokaryotes reproduce asexually and divide simply into two cells which are identical to the initial cell
By increasing the number of gene combinations, the probability that favorable combinations will be produced increases – This increases the chance of evolutionary change in a species due to natural selection

22. Early Single-Celled Organisms
Sexual Reproduction vs. Asexual reproduction
Asexual – ease, rate of reproduction, energy efficient
Sexual – genetic diversity, increase in evolution

23. Paleozoic Era
Fossil evidence shows a very diverse life during this era
Was initially thought that much of this life originated during this era
Actually came about much earlier

24. Cambrian Period Cambrian Explosion
The explosion and diversification of life during this period
Organisms had shells and outer skeletons
Common organisms:
Jellyfish, worms, sponges
Brachiopods, trilobites

25. Ordovician and Silurian Periods
Ancestors of modern octopi and squid appeared
Arthropods became the first land animals
Jawless fishes became the first vertebrates
Plants evolved from aquatic ancestors

26. Devonian Period Plants began to adapt to drier areas
This allowed for invasion of new habitats
“Age of Fishes”
Many groups of fishes present in the oceans
Vertebrates began to also invade land
Most fishes had jaws, bony skeletons, and scales on their bodies
Sharks appeared late in this period
When fish developed the ability to crawl, they moved to land. These evolved to the amphibians

27. Carbiniferous and Permian Period
Reptiles evolved from amphibians
Winged insects began to appear
Dragonflies and cockroaches
Plants became abundant and when they died, their remains are now coal
At he end of this period there was a mass extinction. As much as 95% of the complex life in the oceans disappeared
This extinction is believed to have resulted from increased concentrations of CO2 in the atmosphere from a comet strike or metorite

28. Mesozoic Era Lasted approximately 180 million years
This era is marked by two main features
Dinosaurs
Flowering plants

29. Triassic Period
Fishes, insects, reptiles, and cone-bearing plants were prominent
“Age of the Reptiles”
Coelophysis – meat eater
Mammals first appeared – mouse or shrew style

30. Jurassic Period Dinosaurs the prominent life form
Ruled the earth for about 150 million years
Many scientists think that birds are close relatives

31. Cretaceous Period Dinosaurs still present New life came about:
Leafy tress
Shrubs
Small flowering plants
Another mass extinction brought this period to and end
More than half the plant and animal groups wiped out
Extinction brought on by another impact, but the extinction was not as thorough

32. Cenozoic Era About 65 million years ago Mammals evolved
Could live on land, in water, and even the air
Tertiary Period
Warm and mild climate
Whales and dolphins evolved
Quaternary Period
Climate cooled – ice ages
Earth warmed up about 20,000 years ago
Homo sapiens – 200,000 years ago in Africa

33. Extinction 99% of all species that ever existed are extinct
Extinctions happen for reasons
Resources
Environments change
Each extinction brings an opportunity for other species to succeed

34. Primate Evolution Common Ancestors
Primates are mammals with flexible hands and feet
Divided into two groups
Prosimians
Anthropoids

35. Primate Evolution Promisians Anthropoids Oldest primate group
Active at night
Lemurs, tarsiers
Anthropoids
Divided into old and new world monkeys as wells as hominoids
Hominids can be even further divided
Lesser apes (gibbons)
Greater apes (gorillas)
Hominids (humans)
New world monkeys live in trees and are native to the Americas
Old world monkeys most travel and forage on the ground – also have large brains

36. Primate Evolution Bipedalism Walking upright, on two legs
Came before larger brains and tool manipulation
Allowed to reach higher into trees, freed the hands

37. Primate Evolution Early Human Fossils Two important genus Homo habilis
Australopithecus
Homo habilis
Homo neanderthalensis
Neanderthals
Homo sapiens
Modern humans
Homo habalis – handy man for the stone tools that he used-lived in Kenya and Tanzania-larger brain than that of Australapithecus
Neanderthals were found in the Neanderthal valley of Germany-coexisted with Homo sapiens

38. Primate Evolution Human Evolution
Modern humans came about 100,000 years ago
Came out of Ethiopia
Brain was key to evolution
Enlarged skull and brain

39. Primate Evolution Australopithecus afarensis Homo erectus
A. Afarensis is one of the better known early hominid species – lived 3-4 million years ago in Africa- brain about the size of a modern day monkey – human like limbs
H. Neaderthalensis and H. sapiens coexisted – could have been competition for resources that forced extinction
Homo neanderthalensis
Homo sapiens