Objective: Chapter 25- History of Life on Earth
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Transcript of Objective: Chapter 25- History of Life on Earth
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Objective: Chapter 25- History of Life on Earth
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Early Earth
Oceans: Near boiling
Lightening Storms
Volcanoes
Atmosphere: Water Vapor, carbon monoxide, carbon dioxide, nitrogen, methane, NO OXYGEN
What was missing?!
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Experiments of Stanley Miller and Harold Urey (1953)
• Experiments showed that amino acids and other organic molecules could form on a lifeless earth
• Proposed that conditions on Earth could have generated organic molecules that gave rise to the 1st organisms.
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Fig. 25-2
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Abiotic Synthesis of Macromolecules
• Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock (amino acids form proteins)
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Early Lipids
• Early organic molecules included lipids• Lipids form bubbles in the water• These bubbles enclosed RNA, a primitive cell
forms
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Protobiont
• Abiotically created molecules within a membrane
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Fig. 25-3
(a) Simple reproduction by liposomes (b) Simple metabolism
Phosphate
Maltose
Phosphatase
Maltose
Amylase
Starch
Glucose-phosphate
Glucose-phosphate
20 µm
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1st polymers were RNA
Short RNA molecules can assemble spontaneously from nucleotide monomers and were probably the 1st polymers to form
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Self-Replicating RNA and the Dawn of Natural Selection
• The first genetic material was probably RNA, not DNA
• RNA molecules called ribozymes have been found to catalyze many different reactions
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The Fossil Record
• Sedimentary rocks are deposited into layers called strata and are the richest source of fossils
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Fig. 25-4Present
Dimetrodon
Coccosteus cuspidatus
Fossilizedstromatolite
Stromatolites Tappania, aunicellulareukaryote
Dickinsoniacostata
Hallucigenia
Casts ofammonites
Rhomaleosaurus victor, a plesiosaur
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• Few individuals have fossilized, and even fewer have been discovered
• The fossil record is biased in favor of species that– Existed for a long time– Were abundant and widespread– Had hard parts
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How Rocks and Fossils Are Dated
• Sedimentary strata reveal the relative ages of fossils
• The absolute ages of fossils can be determined by radiometric dating
• A “parent” isotope decays to a “daughter” isotope at a constant rate
• Each isotope has a known half-life, the time required for half the parent isotope to decay
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Fig. 25-5
Time (half-lives)
Accumulating “daughter” isotope
Remaining “parent” isotopeF
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1 2 3 4
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1/41/8 1/16
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Table 25-1
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The First Single-Celled Organisms
• The oldest known fossils are stromatolites, rock-like structures composed of many layers of bacteria and sediment
• Stromatolites date back 3.5 billion years ago
• Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2.1 billion years ago
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Photosynthesis and the Oxygen Revolution
• Most atmospheric oxygen (O2) is of biological origin
• The source of O2 was likely bacteria similar to modern cyanobacteria
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• This “oxygen revolution” from 2.7 to 2.2 billion years ago– Posed a challenge for life– Provided opportunity to gain energy from light– Allowed organisms to exploit new ecosystems
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The First Eukaryotes
• The oldest fossils of eukaryotic cells date back 2.1 billion years
• The hypothesis of endosymbiosis proposes that mitochondria and plastids (chloroplasts) were formerly small prokaryotes living within larger host cells
• An endosymbiont is a cell that lives within a host cell
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Fig. 25-9-4
Ancestral photosyntheticeukaryote
Photosyntheticprokaryote
Mitochondrion
Plastid
Nucleus
Cytoplasm
DNAPlasma membrane
Endoplasmic reticulum
Nuclear envelope
Ancestralprokaryote
Aerobicheterotrophicprokaryote
Mitochondrion
Ancestralheterotrophiceukaryote
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• Key evidence supporting an endosymbiotic origin of mitochondria and plastids:
– Similarities in inner membrane structures and functions
– These organelles transcribe and translate their own DNA
– Their ribosomes are more similar to prokaryotic than eukaryotic ribosomes
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The Cambrian Explosion
• The Cambrian explosion refers to the sudden appearance of fossils resembling modern phyla in the Cambrian period (535 to 525 million years ago)
• The Cambrian explosion provides the first evidence of predator-prey interactions
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The Colonization of Land
• Fungi, plants, and animals began to colonize land about 500 million years ago
• Arthropods and tetrapods are the most widespread and diverse land animals
• Tetrapods evolved from lobe-finned fishes around 365 million years ago
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Continental Drift
• At three points in time, the land masses of Earth have formed a supercontinent: 1.1 billion, 600 million, and 250 million years ago
• Earth’s continents move slowly over the underlying hot mantle through the process of continental drift
• Oceanic and continental plates can collide, separate, or slide past each other
• Interactions between plates cause the formation of mountains and islands, and earthquakes
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• The break-up of Pangaea lead to allopatric speciation
• The current distribution of fossils reflects the movement of continental drift
• For example, the similarity of fossils in parts of South America and Africa is consistent with the idea that these continents were formerly attached
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Mass Extinctions
• The fossil record shows that most species that have ever lived are now extinct
• At times, the rate of extinction has increased dramatically and caused a mass extinction
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• The Permian extinction defines the boundary between the Paleozoic and Mesozoic eras
• This mass extinction occurred in less than 5 million years and caused the extinction of about 96% of marine animal species
• This event might have been caused by volcanism, which lead to global warming, and a decrease in oceanic oxygen
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Is a Sixth Mass Extinction Under Way?
• Scientists estimate that the current rate of extinction is 100 to 1,000 times the typical background rate
• Data suggest that a sixth human-caused mass extinction is likely to occur unless dramatic action is taken
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Consequences of Mass Extinctions
• Mass extinction can alter ecological communities and the niches available to organisms
• It can take from 5 to 100 million years for diversity to recover following a mass extinction
• Mass extinction can pave the way for adaptive radiations
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Worldwide Adaptive Radiations
• Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs
• The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size
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Regional Adaptive Radiations
• Adaptive radiations can occur when organisms colonize new environments with little competition
• The Hawaiian Islands are one of the world’s great showcases of adaptive radiation
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Fig. 25-18
Close North American relative,the tarweed Carlquistia muirii
Argyroxiphium sandwicense
Dubautia linearisDubautia scabra
Dubautia waialealae
Dubautia laxa
HAWAII0.4
millionyears
OAHU3.7
millionyears
KAUAI5.1
millionyears
1.3millionyears
MOLOKAIMAUI
LANAI