History of life on Earth

• Pieces of evidence suggested that if Earth is 4.5 billion years old from radiometric dating of the oldest rock found on it, life on Earth began most probably 3.5 billion years ago
• Stromatolites


  Living rock samples that scientists have discovered and dated to age up to 3.5 billion years old, identical to a mat of microbes with layers of microbes and their byproducts
• Life had first appeared as simple microbes and bacteria, which have their point of origin from the chemical reactions and building of organic compounds on deep-sea vents of ancient Earth, which as evidence suggests occurred from 3.5 billion years ago
• Fossils


  Actual remains of organisms such as bones, teeth, shells, and leaves, or even traces of their past activities such as footprints and nests, usually as old as the rocks where they were embedded or imprinted
• Absolute Dating


  Obtaining the actual age of the fossils and rock through radiometric dating or the use of the concept of half-life and the radioactive decay of elements
• Relative Dating


  Obtaining the relative age of the rocks or samples, it does not tell the actual age but only uses some principles of comparison
• Law of Superposition


  • The youngest rocks are found on top of the layers and the oldest rocks are found on the bottom
• Law of Original Horizontally


  • Sedimentation or layering of the rocks occur horizontally; if tilting, breaking, or folding of rocks or its layer occur, it happened recently after the horizontal layering
• Law of Cross-Cutting Relationship


  • If the rocks under investigation have a cut from igneous rock intrusions, then the intrusions or fault breaks are younger than the rock being investigated
• Continental Drift


  Slow, incessant movement of Earth's crustal plates on the hot mantle
• Plate Tectonics


  Movement of Earth's crustal plates, also associated with volcanoes and earthquakes
• Mass Extinction


  May have been a result of an asteroid impact or volcanic activity
• Geological Time Scale


  A model of chronological dating that describes the timing and relationships of major biological and geological events that have occurred during the Earth's history
• EON


  Largest division of the geologic time scale; half billion - nearly 2 billions of years
• PRECAMBRIAN


  Largest division of the geologic time scale; half billion - nearly 2 billions of years
• HADEAN


  Occurred 4.6 billion to 4 billion years ago, during which the solar system was forming within a cloud of dust and has known as SOLAR NEBULA which eventually spawned planets and etc.
• Archean


  Started between 4 billion and 2.5 billion years ago, the first form of life on our planet was created in the oceans
• Proterozoic


  Started 2.5 billion years ago and ended 543 million years ago
• Phanerozoic Eon


  The eon of "everything" after the Cambrian Explosion
• ERA


  Divisions that span time periods of tens to hundreds of million of years
• Paleozoic


  "Ancient or old life"; started more than 540 million years ago, many organisms that have emerged during this time were INVERTEBRATES
• PERIODS


  A division of geologic history with spans of no more than 100 million years
• CAMBRIAN EXPLOSION


  It began with a spectacular burst of new life
• CAMBRIAN PERIOD


  544-505 million years ago, following the Precambrian mass extinction, there was an explosion of new kinds of organisms in the Cambrian
• ORDOVICIAN PERIOD


  505-440 million years ago, the oceans were filled with invertebrates of many types, the first fish evolved
• SILURIAN PERIOD

  440-410 million years ago, in the oceans, corals appeared and fish continued to evolve
• DEVONIAN PERIOD


  410-360 million years ago, the first seed plants evolved. Seeds had a protective coat and stored food to help them survive. Seed plants eventually became the most common type of land plants
• CARBONIFEROUS PERIOD


  360-290 million years ago, widespread forests of huge plants left massive deposits of carbon that eventually turned to coal
• MISSISSIPPIAN


  The last time limestone was deposited by widespread seas on the North American continent
• PENNSYLVANIAN


  The evolution of terrestrial plants and animals had advanced to the point where true forests were developed in lowland, coastal sites
• PERMIAN PERIOD


  290-245 million years ago, all the major land masses collided to form a supercontinent called PANGEA, temperatures were extreme, and the climate was dry
• CENOZOIC ERA


  Recent life"; started 65 million years ago and continues up to the present
• Tertiary


  65-1.8 million years ago, Earth's climate was generally warm and humid, mammals evolved to fill virtually all niched vacated by dinosaurs, many mammals increased in size
• Quaternary Period


  1.8 million years ago - present, Earth's climate cooled, leading to a series of ice ages, sea levels fell because so much water frozen in glaciers, this created land bridges between continents, allowing land animals to move to new areas
• NEOGENE


  "New born," was designated as such to emphasize that the marine and terrestrial fossils found in the strata of this time were more closely related to each other than to those of the preceding period
• PALEOGENE


  Divided into 2 divisions
• Mesozoic


  Cretaceous Period - Flowering plants (angiosperms) appear; many groups of organisms, including dinosaurs, become extinct at the end of period (Cretaceous extinction), Jurassic Period - Gymnosperms continue as dominant landscape: radiation of dinosaurs, Triassic Period - Gymnosperms continue as dominant plants; dinosaurs abundant and diverse
• Epoch


  Pleistocene - Ice ages; humans appear, Pliocene - Apelike ancestors of humans appear, Oligocene - Continued radiation of mammals and angiosperms, Miocene - Origins of many primate groups, including apes, Paleocene - Angiosperm dominance increases; continued radiation, Eocene - Major radiation of mammals, birds, and pollinating insects