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The History of Life
Chapter 12
The Fossil Record
Fossil Forming Perminerilization Natural Casts Trace Fossils Amber preserved
fossils Preserved remains
Most fossils form in sedimentary rock
The Fossil Record
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
The Fossil RecordRadiometric Dating
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
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
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
Geologic Time Scale
Evolutionary time is represented by the Geologic Time Scale This orders rock by
ageDivided into units
based on order rocks and fossils were formed
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
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
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
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
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
Origin of Life
Meteorite Hypothesis Amino acids have
been found in meteorites
Suggests that amino acids could have been present when Earth formed
Origin of LifeIron 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
Origin of Life
Lipid Membrane Hypothesis Lipids tend to form
spheres – liposomes
These spheres could enclose organic molecules
Give rise to cells
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
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
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
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
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?
Early Single-Celled Organisms
Sexual Reproduction vs. Asexual reproduction Asexual – ease, rate
of reproduction, energy efficient
Sexual – genetic diversity, increase in evolution
Paleozoic EraFossil evidence shows a very
diverse life during this eraWas initially thought that much of
this life originated during this eraActually came about much earlier
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
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
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
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
Mesozoic Era
Lasted approximately 180 million years
This era is marked by two main features Dinosaurs Flowering plants
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
Jurassic Period
Dinosaurs the prominent life form
Ruled the earth for about 150 million years
Many scientists think that birds are close relatives
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
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
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
Primate Evolution
Common Ancestors Primates are
mammals with flexible hands and feet
Divided into two groups• Prosimians• Anthropoids
Primate Evolution
Promisians 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)
Primate Evolution
Bipedalism Walking upright, on
two legs Came before larger
brains and tool manipulation
Allowed to reach higher into trees, freed the hands
Primate Evolution
Early Human Fossils Two important genus
• Homo• Australopithecus
Homo habilis Homo
neanderthalensis• Neanderthals
Homo sapiens• Modern humans
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
Primate Evolution
Australopithecus afarensis Homo erectus
Homo neanderthalensis Homo sapiens
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