Origin Of The Earth And Evolution Of Life PDF

Origin of the Earth and Evolution of Life Origin of Life Environmental conditions of primitive Earth Earth was “born” about 4.5 billion years ago. The planets probably formed from debris cast off from our Supernova following its condensation from interstella...

Origin of the Earth and Evolution of Life Origin of Life Environmental conditions of primitive Earth Earth was “born” about 4.5 billion years ago. The planets probably formed from debris cast off from our Supernova following its condensation from interstellar gas and dust of a nebula about 5–7 Bybp. At first, Earth was semi-molten, but gradually cooled enough to form a solid rock crust The oldest rocks are 3.964 Bybp.  Decay of radioactive elements of Earth caused partial melting of the planet’s interior, with denser materials making up the core. Differential temperatures of the core and crust set convection currents in motion in the mantle. The conditions of Earth upon its formation about 4.5 billion years ago is described as “hellish”. Earth during early years: extremely hot the surface mostly consisted of molten rocks the atmosphere contained gases with only small traces of oxygen.  continually bombarded by radiations and meteors. not conducive to any form of life. Earth’s position relative to the Sun ensure that the planet was conducive to life. “habitable zone” - It radiates light and heat, or solar energy, which makes it possible for life to exist on Earth. Water vapor was present in the Earth’s atmosphere and large bodies of water formed on the planet’s surface. Gradually causes: absorbed the carbon dioxide from the atmosphere. lowering the levels of gases trapping heat = regulates the planet’s temperature.  As Earth cooled, there was a period of intense volcanic activity that released gases into the primitive atmosphere, primarily: ammonia = NH3 carbon monoxide = CO hydrogen sulfide = H2S methane = CH4 nitrogen = N2 water vapor = H2O  As the rate of radioactive decay slowed, water vapor condensed and fell through the atmosphere, dissolving gases and forming a “poisonous” rain. Run-off of rainwater from the land carried dissolved minerals into a shallow water/ocean. The collective materials in the water/ocean formed a “primordial soup”.  Earth’s surface was bombarded by solar energy, especially ultraviolet (UV) radiation. Intense electrical storms generated lightning that assaulted the surface. Together, the UV and lightning provided energy necessary to arrange simple molecules of CH4, NH3, PO4 salts, and H2O into the basic building blocks of organic compounds, and then into complex macromolecules.  This chemical evolution of organic molecules is called abiogenesis  Life began with the first self-replicating “organism” The earliest organism may have been no more than a ribozyme A ribozyme is an RNA molecule capable of enzymatic actions, e.g., the self-splicing introns of some RNAs, which can excise themselves from the molecule without the help of protein enzymes.  These first self-reproducing organisms appeared about 3.5 Bybp They were prokaryotes and anaerobic heterotrophs that fed on organic molecules in the primordial soup [anaerobic, without oxygen] [heterotrophs, consume organics from other sources]  Early life forms were continuously bombarded by UV radiation, causing mutations that produced new life forms As new life forms evolved, the predatory mode appeared Consumption of prey organisms required catabolism of their organics through the process of respiration  The ozone accumulated into the ozone layer in the stratosphere, and blocked most of the UV radiation from penetrating to surface Formation of the ozone layer enabled development of terrestrial life forms Other organisms developed the ability to utilize energy released from breaking chemical bonds to manufacture their own organic compounds in the process called chemosynthesis  About 2.7 Bybp, still other organisms developed the ability to utilize energy from sunlight to manufacture their own organic compounds in the process called photosynthesis Photosynthesis released a new gas into the atmosphere, oxygen CO2 + H2O → C6H12O6 + O2 carbon water glucose oxygen dioxide  At first, all of the oxygen released by photosynthesis reacted with iron in the lithosphere Gradually, free elements reached oxidized states, and O2 began to accumulate in the atmosphere Because oxygen interferes with anaerobic respiration, another great change in life occurred, the development of aerobic respiration C6H12O6 + O2 → energy + CO2+H2O  The oxygen-rich atmosphere and aerobic respiration are thought to have led to the evolution of eukaryotes  Refers to the separation of the Earth’s Continents Drifting across oceanic bed