Chapter 18

 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 _________________

 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)

 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

 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

 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 __________

 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

 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 __________ _________________

 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: __________________________________ __________________________________________

 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 _________________________

 Lived ______________ years ago  Prokaryotic, _____________________  Anaerobic, can live without _______, ___________________  Heterotroph/Autotroph  Not _______________________

 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 ____________________

 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, ______________

 Difficult to find _____________in fossils  Eukaryote cells are _______________  Scientists look for ______________  ______________________________________________  Example: steroids only found in eukaryotes  Oldest microfossil of eukaryote is _________years old

 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 __________________________________________

 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 →

 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 ___________________________

 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 _______________________

 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 _________

 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

 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.