Chapter 25 Flashcards
Origin of the universe
Big Bang 13.7 BYA
Milky way formation
~4.6 BYA. Young collection of stars, dust, planets. Act as a unit and rotate around
Earth
formed about 4.5 BYA. Beginning was hot and violent. Carbon and water burned off. Comets struck often. Gravitation still pulling everything together
Hadean period
Asteroids common. Vaporized entire oceans. Dramatic changes from fiery to frozen (snowball earth). Not hospitable for life
No rocks exist.
Archean period
Fossil evidence of life 3.2 - 3.5 BYA, maybe 3.9 but no rocks
Oldest prokaryote fossils
3.5 BYA
First multicellular organism
700 MYA
Cyanobacteria
2.2 BYA
Appearance of oxygen in atmosphere
2 BYA
Oldest definite fossils of eukaryotes
1.5 BYA
Extraterrestrial hypothesis
“Panspermia” Organic molecules have extraterrestrial origins idea. Meteorites on earth have carboxylic and sulfonic acids
4 Stages in the chemical evolution of life
1 Formation of small organic molecules, nucleotides, and amino acids
2 Organic molecules formed polymers. DNA, RNA, and proteins.
3 Polymers were enclosed in membranes.
4 Polymers and membranes developed cellular properties
Comet impacts
Given rise to more complex organic molecules. Energy important for building. 100,000 atm vs 100 atm bottom of ocean
Stage 1 formation of organic molecules
Current hypotheses suggest organic molecules formed spontaneously from earth materials. Formed and/or sequestered in H2O.
Primordial or Prebiotic soup - mixture of chemical and environmental forces to form bonds.
Doesn’t need to have clay
Reducing atmosphere on early earth
CO2, carbon monoxide CO , Nitrogen N2, water vapor H2O, Hydrogen H2, hydrogen sulfide H2S, (Methane? CH4, ammonia? NH3)
NO OXYGEN
Miller-Urey experiment
Were successful Able to create AA’s. Boiling water with vacuum, energy source (electrical discharge) with gases (H2O, H2, CH4, NH3), then cold water and condenser and captured primordial soup.
Stage 2 Clay
Organic polymers may have formed on clay surfaces.
Clay properties: Has a slight charge that can attract and hold other molecules, create bonds. Contains small amounts of metal atoms (copper, iron, or zinc). These metal atoms function as catalysts facilitating the dehydration reactions that link AA’s. Able to store energy absorbed from radioactive decay and then discharge energy at times when the clay changes temperature or degree of dehydration.
Stage 3
Coacervates
Protobionts
Cell-like structures may have formed when polymers were enclosed by a membrane-like boundary. Have to have cell membrane surrounding proteins and AA’s.
Coacervates- bubbles, can have chemical reactions.
Protobionts are aggregates of probiotically produced molecules and macromolecules with boundaries.
Stage 4
Liposomes
RNA 3 key functions
Cellular characteristics may have evolved in an RNA world
Evolving single strands is easier than 2 strands. Lots of RNA floating around.
Liposomes - develop lipid bilayer, barrier to regulate. Grow and divide on clay. When RNA is present of clay, liposomes form around it to form early cell.
RNA 1 Ability to store information in its nucleotide sequence.
2 Can replicate itself by base pairing.
3 Can perform a variety of enzymatic functions
Deep-sea vent hypothesis
Hydrothermal vents (Hydrogen, CO2, Suflur) + vents + energy= H2S and cold H2O to hot H2O
H2O temps known to be suitable for organic chemistry
Would happen near plates that are separating releasing lava and gases.
First organisms and evidence
Prokaryotic, probably aquatic anaerobic heterotrophs. Microfossils (microscopic life)
Isotopic data (sequester carbon 12 changes, ratios of isotopes in atmosphere)
Biomarkers - evidence of life, look for organic molecules, hydrocarbons like lipids in rock formations in Australia
Aquatic anaerobic heterotrophs
Probably first cells. No oxygen. Organism that consumes other organisms. Derives energy from complex organic substances. Consumed many kinds of organic molecules floating in biotic soup. Final e acceptor is organic material.
Autotrophs
Evolved at some point. Consume light or chemical energy and create sugars. Favored by selection over heterotrophs.
Form nutritional organic substances from simple inorganic substances. Reduced CO2 using electrons from hydrogen sulfide. Released sulfur as waste product
Cyanobacteria
Autotrophs, began to split water for electrons. Released O2 as waste product. O2 Toxic to organisms. Earth goes from anaerobic to aerobic conditions. Big changes build O2 and chemical reaction to create Ozone (O3) and protect from radiation.
Results of releasing O2 as waste product
Oceans and earth crusts “rusted”. Obligate anaerobes were poisoned. Aerobic respiration evolved. Carbon cycle began. Ozone was generated in the upper atmosphere. Land now hospitable
Stromatolites
Fossilized and living. Colonies of cyanobacteria layered with calcium carbonate to form rock like columns. Lived as layers, die, and new layers grow on top, etc. etc.
Eukaryotic evolved -
During the Proterozoic eon (late ends with 3rd snowball earth, glaciation) Cambrian explosion of diversity started around 500 MYA. Compartmentalization within cell! Major innovations to successfully move from water to terrestrial environments, gills and gas exchange through skin, stomata in plants, safe from UV radiation (ozone layer) from photo synthesis.
Changes that occur in organisms over time. 2 interacting Factors
1 Genetic changes within populations of organisms, evolution
2 Changes in earth’s environmental conditions - extinctions, adaptations (Opens habitats, adaptive radiation)
Environmental conditions that influence organisms over time
1 Climate/Temp-Ice ages, snowball earth, CO2
2 Atmosphere - changes in oxygen levels
3 Land masses - continental drift
4 Natural disasters - flood, glacier, volcano, meteorites
Endosymbiont theory
Origin of eukaryote. One prokaryote consumed another prokaryote and became a specialized organelle and becomes a eukaryote. Does not breakdown consumed prokaryote
Purple bacteria similar
to mitochondria
Cyanobacterium similar
to genetic sequence of chloroplast
