earth’s early history:
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Earth’s Early History:. The formation of the planet and the beginning of life. An Important Note:. - PowerPoint PPT PresentationTRANSCRIPT
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EARTH’S EARLY HISTORY:The formation of the planet and the beginning of life
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AN IMPORTANT NOTE: These large-scale hypotheses are based on
a relatively small amount of hard evidence. Because of this, these exciting inferences will without doubt develop, improve, and even change over time.
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HOW THE PLANET FORMED
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FORMATION OF PLANET EARTH 4.6 billion years
ago
Cosmic debris
Collisions, compression, decay…HEAT
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FORMATION OF PLANET EARTH Differentiation:
Iron sank
Less dense “floated” to form crust
Least dense = first atmosphere
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EARTH’S EARLY ATMOSPHERE Very different from today’s atmosphere:
Much hotter Frequent volcanic eruptions Little or no oxygen Toxic to us!
vs
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SETTING THE STAGE FOR LIFE 3.8 billion years ago, Earth cooled, water
in liquid form
Global ocean
Here, life will somehow form!
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ANIMATION
http://www.precisiongraphics.com/portfolio/animation/
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THE FIRST ORGANIC MOLECULESLife cannot begin without these!
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HOW DO WE GET LIFE?
Living things can come from non living things
All living things must come from a living thing
Spontaneous Generation Biogenesis
In the mid 1600’s Francesco Redi decided to find out…
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REDI’S EXPERIMENT: DO FLIES SPONTANEOUSLY GENERATE ON ROTTING MEAT?
Uncovered jars with rotting meat
Covered jars with rotting meat
Air could pass through but not flies
Control Group Experimental Group
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RESULTS: BIOGENESIS
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TWO MORE EXPERIMENTS…1700’SLazzaro Spallanzani: Tried to prove micro-
organisms did not come from a “vital force” in the air
Opponents said that he heated the flasks for too long removing the “vital force”
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FINALLY AN ANSWER…MID 1800’SLouis Pasteur Similar to Spallanzi’s
but allows for the air to continue to be exchanged with the outside
Curve prevents solids from passing into the flask
FINALLY Accept Biogenesis
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THE FIRST ORGANIC MOLECULES Could organic molecules have evolved under
the conditions of early Earth?
2 American chemists tried to answer that: Miller and Urey
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MILLER AND UREY EXPERIMENT Showed that
mixtures of organic compounds necessary for life can be created from simpler compounds that were present on early Earth
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IMPORTANT NOTE: Not accurate!
Corrected, showed that organic compounds CAN form under these conditions…even cytosine and uracil, two bases found in RNA!
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LIFE’S ORIGINS
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PROTEINOID MICROSPHERES Organic molecules forming bubbles
Selectively permeable membranes
Can store and release energy
Similar to modern cell
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RNA AND DNA RNA molecules can form
Theory: could these early forms of RNA (that predate more complex DNA and RNA molecules) have found a home inside a microsphere?
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OXYGEN
The fossil record photosynthetic bacteria
Rising levels of oxygen in atmosphere
The rise of oxygen drove some life forms to extinction (it was toxic to them), while other life forms were able to thrive
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THE BEGINNING OF MODERN LIFEEukaryotic Cell Origins
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ORIGIN OF EUKARYOTIC CELLS Prokaryotic cells
Internal membrane nucleus
Cells with a nucleus! The first eukaryotes!!!
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ORIGIN OF EUKARYOTIC CELLS Endosymbiotic Theory
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EVOLUTION OF MULTICELLULAR LIFEThrough 4 eras
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PRECAMBRIAN ERA 650-544 million years ago
Simple anaerobic life forms Photosynthetic life develops adding oxygen
to the atmosphere Eukaryotes appear
Life still only in the sea!
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PALEOZOIC ERA 544-245 million years ago
Diversity of marine life First vertebrates First organisms walked on land Plants and insects appeared Mass extinction – 95% of life dies out!
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MESOZOIC ERA 245-65 million years ago
Appearance of dinosaurs (which later dominate the land on Earth) Small mammals develop Leafy trees, shrubs, and flowering plants
develop Mass Extinction – 50% of life dies out
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CENOZOIC ERA 65 million years ago – present
Plants and insects thrive Mammals adapt to environment well and
dominate life on Earth Appearance of human ancestors Ice age
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BUT HOW DO WE KNOW THIS?Fossilization and Determining Ages
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FOSSILIZATION Fossil = remains or traces of an organism that
died long ago Ways to make a fossil
Sedimentary Rock Amber Volcanic Ash
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SEDIMENTARY ROCK – RELATIVE DATING
Principle of Superposition (1669) – if rock strata (layers) have not been disturbed, the lowest stratum was formed first
Relative Age – age compared to other fossils, determined by location in the strata
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RADIOMETRIC DATING Compare the
amount of a naturally occurring isotope to its decay products.
Absolute Age – age of the rock as determined by radiometric dating
Half Life – Time it takes for half of the material to decay