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History of Life
Chapter 19
The Fossil Record 19.1
• Any evidence of an organism that lived long ago and are now extinct
• Most are formed in sedimentary rocks• Provides info about structure, environment
and way of life
Types of Fossils
Amber-preserved
Imprint
MoldCast
Trace
How are fossils formed?
Dating Earth’s History
Relative Dating• Uses the position of fossils in sediment layers
– Oldest at the bottom layer, youngest on top, not actual age
– Index fossil• an easily recognized and widespread fossil used to
compare the relative ages of rocks, ex. trilobites
Radiometric Dating• Uses radioactive isotopes
(atoms with unstable nuclei that break down or decay)– Half-life – the time required for
half of the radioactive atoms in a sample to decay• Potassium 40, half-life = 1.3
billion years• Carbon 14, half-life = 5730 years
Geologic Time Scale
Geological Time Scale
• Based on both relative and absolute dating
• Major divisions– Eons– Eras– Periods
Precambrian Era
• Starts 4.7 bya• Life began• Accounts for 90 % of Earth’s history• Primitive prokaryote were the first forms of
life
• Paleozoic Era– Appearance of plants and animals including
fishes, reptiles, amphibians and ferns
• Mesozoic Era– Mammals and dinosaurs– Flowering plants
• Cenozoic Era– Primates– Modern human (200,000 years ago)
Life on a changing planet
• Physical forces– Geological forces (building mountains and
moving whole continents) have altered habitats of living organisms throughout Earth’s history
– Plate tectonic theory• Explains the movement of continents (3 cm/year)• Africa and South America separated by Atlantic
Ocean
• Biological forces– Actions of living organism have changed
conditions in the land, water, and atmosphere of the Earth
– Earth cooled as CO2 decreased; used by early photosynthetic organisms
Patterns and Processes of Evolution 19.2
• What processes influence survival or extinction of species and clades?– Clades
• Group of species that includes a common ancestor and all descendants of that ancestor, living or extinct.
• The more varied the species (more diversity) in a particular clade are, the more likely the clade is to survive environmental change.
Patterns of Extinction
• Background extinction– Slow steady process of natural selection
• Mass extinction– An event during which many types of living
things suddenly die out– Makes new habitats and resources available to
organisms left after a major catastrophe
Rate of Evolution
Gradualism• Species originate through a slow and steady change
of adaptations
Punctuated Equilibrium
• Speciation experience long, stable periods interrupted by brief periods of rapid evolutionary change
Patterns of Macroevolution
Adaptive radiation
• When a single species or a small group of species evolves over a relatively short time into several different forms that live in different ways.
Hawaiian honeycreepers
Convergent Evolution• Distantly related organisms evolve similar
traits• Unrelated species occupy similar
environments in different parts of the world
Coevolution
• Process by which two species evolve in response to changes in each other over time– Ex. Flowers and pollinators (birds, bees, etc.)
Earth’s Early History 19.3
• About 4.5 billion years old• Formed from cosmic debris colliding• Earth cooled enough for solid rocks to form
and water vapor to condense and fall as rain, produce oceans
• Earth’s atmosphere was primarily composed of – Carbon dioxide, water vapor, nitrogen
• Hypotheses on how life began
Stanley Miller and Harold Urey’s experiment
• Produced 21 amino acids—building blocks of proteins.
• Proved incorrect• Nonlife to life is a
big leap!
Microspheres
• Proteinoid microspheres– Contain selective permeable membrane
• Water passes through
– Store and release energy– About 3.8 billion years ago
RNA and DNA
• Hypothesized that RNA formed before DNA
Origin of eukaryotic cells
Endosymbiotic theory• Prokaryotes were the ancestors of
eukaryotic organisms• Small prokaryotes began living inside the
larger cells
– Mitochodria • evolved from endosymbiotic prokaryotes that are
able to use oxygen to generate energy-rich ATP
– Chloroplasts• Evolved from endosymbiotic prokaryotes had the
ability to photosynthesize
Modern evidence
• Lynn Margulis (1960)– Supported endosymbiotic theory– Mitochondria and chloroplasts have DNA
similar to bacterial DNA– Both have ribosomes resembling those of
bacteria– Reproduce by binary fission when cells
containing them divide by mitosis