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Published byLindsay Booth Modified over 8 years ago
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Chapter 18
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Earth formed about _____________years ago (determined by _______________________) Early atmosphere contained little or no oxygen (oldest rocks show no evidence of iron oxidation) Presence of water (_____________indicate they formed in presence of water) Constant hail of _________________
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All life consists of: ___________, __________, _______________, _________________ Where did the subunits of the first life come from? There are several possibilities: ___________________atmospheric reactions _________________from space Reactions at deep-sea _______________________ (underwater hot spring)
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1953 Miller and Urey simulated Earth’s early atmosphere by filling a reaction chamber with gases and water vapor. Zapped it with sparks (simulating lightning) Within a week amino acids and organic mols formed
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Organic material that formed in interstellar clouds of ____, ______and _______could have been carried to Earth on meteorites During Earth’s early years meteorites fell to Earth ____________of times more frequently than today
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Deep underwater openings in ocean where mineral-rich water heated by __________________ streams out Reactions in the super hot, mineral- rich water near deep-sea hydrothermal vents also produce ___________________________ Simulated experiments combining hot water with carbon monoxide (CO), potassium cyanide (KCN), and metal ions formed _____________ within a __________
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Similarities in ____________, ___________, and ______________among all life indicate descent from a common cellular ancestor Experiments demonstrate how traits and processes seen in all living cells could have begun with __________and __________reactions among non-living collections of molecules
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Proteins that speed metabolic reactions might have first formed when amino acids stuck to clay, then bonded under the _____________________ Metabolism may have begun in rocks near deep- sea hydrothermal vents when iron sulfide in the rocks donated electrons to dissolved __________ _________________
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Early mols would have floated away if not enclosed Modern cells: ____________________ If first reactions in rock chambers: Rock would act as ___________________ Lipids produced in chamber would accumulate and ______________________ May have been first __________________ Protocell: __________________________________ __________________________________________
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All modern cells have a genome of DNA Protein synthesis depends on DNA, which is built by ___________________ How did this cycle begin? An RNA world, a time in which RNA was the _________ ___________, may have preceded DNA-based systems Ribozymes: ___________________________________ So why mutate from RNA to DNA RNA _______________more easily RNA _______________more frequently DNA made larger, more _________________________
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Lived ______________ years ago Prokaryotic, _____________________ Anaerobic, can live without _______, ___________________ Heterotroph/Autotroph Not _______________________
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Divergence to domains Bacteria and Archaea occurred very early in history of life ___________________________________ Oldest proposed cell ___________________: 3.5bil year old filaments in rocks may be fossilized chains of _______________________ OR 3.4bil year old ____________________
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Stromatolites ______-shaped structure, composed of layers of _____, ___________and __________(matter that settles to the bottom of a liquid) Photosynthetic bacteria living in shallow sunlit water form a mat that traps sediment Sediment covers bacteria Bacteria grows through it, ______________
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Difficult to find _____________in fossils Eukaryote cells are _______________ Scientists look for ______________ ______________________________________________ Example: steroids only found in eukaryotes Oldest microfossil of eukaryote is _________years old
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2.5bil years ago O2 from cyanobact started to accumulate in _______and ________ Interferes with self-assembly of complex ______________________ Prevented evolution of new life from ___________ molecules Presence of oxygen gave organisms that thrived in ______________ conditions an advantage Formation of an ozone (O3) layer in the upper atmosphere protected Earth’s surface from __________________________________________
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Prokaryote DNA __________________________ Eukaryote DNA _________________________ Internal membranes typical of eukaryotic cells may have evolved through infoldings of ________________ of prokaryotic ancestors Existence of some ______________________________ supports this hypothesis Nucleus-like structure in prokaryote →
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Endosymbiont hypothesis Mitochondria and chloroplasts resemble bacteria in __________________________ Descendent from ___________________ One species lives and reproduces __________________ Over generations, host and guest cells come to _______ upon one another for ___________________________
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Evidence to support endosymbiont hypothesis Microbiologist Kwang Jeon grew amoebas infected by a rod-shaped bacterium – eventually, after 5 years the amoebas came to rely on the bacteria for some _______________________
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Encompasses almost all of Earth’s history From ___________years ago to Cambrian (____________) Life arose and ___________ By the close of this period, bacteria, archaea, and eukaryotes lived in the _________
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Astrobiologists study properties of the ancient Earth that allowed life to arise, survive, and diversify Astrobiology ▪ _____________________________________________________ _____________________________________________________ Presence of cells in deserts and deep below Earth’s surface suggests life may exist in similar settings on other planets
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The Mars-like landscape of Chile’s Atacama Desert. Scientist Jay Quade, visible in the distance at the right, was a member of a team that found bacteria living beneath this desert soil.
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