E VOLUTION – H ISTORY OF LIFE ON EARTH

 History of Life on Earth  Chemical Evolution (pre-biotic evolution) –  There are four processes needed for the spontaneous origin of life on Earth: 1.The non-living synthesis of. 2.The assembly of these molecules into 3.The origin of 4.The packaging of these molecules into D.1.1 – Describe four processes needed for the spontaneous origin of life on Earth

 Alexander Oparin (Russian) and John B. S. Haldane (England) were the first scientists (independently) to advance the idea that (1920’s) They noted that the oxygen-rich atmosphere of today would not have permitted the spontaneous formation of organic molecules They speculated that the Earth’s early atmosphere was very in the form of hydrogen gas (H 2 ), methane (CH 4 ), and ammonia (NH 3 ) – also contained carbon dioxide (CO 2 ), water vapor (H 2 O), carbon monoxide (CO), and nitrogen (N 2 )

 Conditions on primordial Earth  Earth is about years old  Earth was very hot when first formed

 Four requirements must have existed for chemical evolution: 1. – Earth’s early atmosphere was probably strongly reducing which would cause any free oxygen to react and form oxides and be removed from the atmosphere 2. – early Earth was a place of high energy violent thunderstorms with torrential rainfall widespread volcanic activity bombardment from meteorites (caused cataclysmic changes in crust, ocean, and atmosphere) intense radiation (including UV radiation, since there was no ozone layer and younger suns emit more UV light)

3. – water, dissolved inorganic minerals (present as ions), and the gases present in the early atmosphere 4. – Earth is approximately 4.6 billion years old, the earliest traces of life are approximately 3.8 billion years old

 Oparin and Haldane’s hypothesis is tested by Stanley Miller and Harold Urey in the 1950’s  They designed a  They exposed an atmosphere rich in H 2, CH 4, H 2 O, and NH 3 to an  Analysis of the chemicals produced in a week revealed that D.1.2 – Outline the experiments of Miller and Urey into the origin of organic compounds.

 Some believe that the organic molecules needed for life may have been  Comets contain a variety of organic compounds  Possible that organic molecules did not form on Earth but rather “hitched a ride” D.1.3 – State that comets may have delivered organic compounds to Earth.

 Once organic molecules were formed they had to  Where on Earth could these organic molecules been able to form in the right conditions? D.1.4 – Discuss possible locations where conditions would have allowed the synthesis of organic compounds.

Recent evidence indicates that organic polymers may have formed and accumulated on (rather than in a “primordial soup” in the sea as described by Darwin) o Clay consists of microscopic particles of weathered rock and may have acted as a site for early polymerizations because it binds organic monomers and contains zinc and iron ions that might have served as catalysts o Lab experiments using clay have confirmed that organic polymers form spontaneously from monomers on hot rock or clay surfaces D.1.4 – Discuss possible locations where conditions would have allowed the synthesis of organic compounds.

Other possible locations include deep-sea hydrothermal vents and volcanoes as further described in your textbook. The possibility of life on other planets is also being researched. D.1.4 – Discuss possible locations where conditions would have allowed the synthesis of organic compounds.

 Protobionts –  Scientists have been able to synthesize several different protobionts  They exhibit many characteristics of living cells – D.1.6 – State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings.

 Two examples of protobionts include and Microspheres are made from and coacervates are formed from Microspheres formed by adding Scientists have heated amino acids without water and produced long protein chains – when water is added, stable microspheres are formed Microspheres show an electrical potential, may absorb materials from the surrounding environment D.1.6 – State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings.

Microspheres may give clues as to the evolution of the Membranes are made of Microspheres can accumulate compounds inside them and become more concentrated than outside, they also attracted lipids and formed a lipid-protein bilayer around them D.1.6 – State that living cells may have been preceded by protobionts, with an internal chemical environment different from their surroundings.

P ROTOBIONTS MicrosphereLiposome

 The first cells probably assembled from organic molecules  Cells were evident in microfossils 3.5 billion years old, perhaps even 3.8 billion years ago  The first cells were  offer more fossil evidence –  Living stromatolite reefs are still found in hot springs and in warm, shallow pools of fresh and salt water

Fossilized Stromatolites – 3.5 billion years old Modern day stromatolites

 A crucial step in the origin of cells was molecular reproduction  Both DNA and RNA can form spontaneously on clay, so… which came first? D.1.5 – Outline two properties of RNA that would have allowed it to play a role in the origin of life.

 RNA is self-catalytic and is believed to have appeared first (according to the RNA World hypothesis) Chemistry of prebiotic Earth gave rise to that functioned both as and for their own replication D.1.5 – Outline two properties of RNA that would have allowed it to play a role in the origin of life.

RNA has catalytic properties – enzymatic RNAs are called o In modern cells, ribozymes help catalyze the synthesis of RNA and process precursors into rRNA, tRNA, and mRNA Ribozymes may have catalyzed the synthesis of RNA, and processed RNA molecules RNA could also catalyze protein formation (catalyzes peptide bonds formation) – protein catalysis of RNA formation happen later D.1.5 – Outline two properties of RNA that would have allowed it to play a role in the origin of life.

 DNA probably evolved after RNA – it’s a more stable molecule May have evolved from Stability of DNA provides advantages as the information storage molecule

 The first cells were probably  They – appeared years ago  The first cells were anaerobes as  As the concentration of free organic molecules in environment, D.1.7 – Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere.

 The which split as a hydrogen donor (purple and green sulfur bacteria)  The first photosynthetic organisms to use H 2 O as a hydrogen donor were the (released )  Source of the first free oxygen in aquatic environment and atmosphere – O 2 existed in significant quantities by 2 billion years ago D.1.7 – Outline the contribution of prokaryotes to the creation of an oxygen-rich atmosphere.

 Aerobes appeared after oxygen increased in atmosphere  Aerobic respiration was “added” to glycolysis after free O 2 became available  Aerobic organisms are much more efficient in  The carbon dioxide produced helped to stabilize concentration of CO 2 and O 2 in atmosphere (by- product of each process – photosynthesis and aerobic respiration – are raw materials for other process)  began to accumulate in upper atmosphere to form ( ) – allowed organisms to live in more shallow water and ultimately on land

 Evolution of Eukaryotic Cells  Evolved from  Endosymbiont Theory – first proposed by Lynn Margulis – suggests that D.1.8 – Discuss the endosymbiotic theory for the origin of eukaryotes.

Aerobic prokaryote (mitochondria) was engulfed by Aerobic prokaryote continued to function and formed a Similar process occurred later with the host cell and (which became ) D.1.8 – Discuss the endosymbiotic theory for the origin of eukaryotes.

 Other evidence: Mitochondria and chloroplasts They have a like prokaryotes They synthesize some of their own proteins using 70s ribosomes, like prokaryotes They have double membrane as expected since cells were taken into a vesicle by endocytosis are similar to of prokaryotes are similar to D.1.8 – Discuss the endosymbiotic theory for the origin of eukaryotes.