Geological Time Scale

• Eon


  Longest subdivision; based on the abundance of certain fossils
• Era

  Next to longest subdivision; marked by major changes in the fossil record
• Period

  Based on types of life existing at the time
• Epoch


  Shortest subdivision; marked by differences in life forms and can vary from continent to continent.
• How the GTS was constructed

  Field observations

  • Fossil records

  • Stratigraphic correlations

  •Radioactive dating

  •Paleomagnetic orientations

  •Orbital revolution pattern of the Earth and

  •The duration of the daily rotation of the earth around its axis.
• Major events of GTS

  • mass extinctions,

  • appearance of new species or genera of life,

  • mountain-building movements • drifting of continents

  • spreading of ocean floors

  • widespread glaciations

  • dominance of certain species

  • massive migration of life between land and water are all considered while accounting the geologic time scale.
• miners


  the first people who needed to understand the geological relationship of diff rocks units
• Nicholas Steno,

  a Danish physician (1638-1687), described how the position of a rock layer could be used to show the relative age of the layer who devised the three main principles that underlie the interpretation of geologic time
• The principle of superposition:


  The layer on the bottom was deposited first and so is the oldest
• The principle of horizontality

  All rock layers were originally deposited horizontally.
• The principle of original lateral continuity


  Originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer.
• strata

  layered rock
• James Hutton


  he thought the surface of the earth was everchanging environment and "the past history of our globe must be explained by what can be seen to be happening now"
• uniformitarianism by James Hutton


  the present is the key to the past
• William Smith


  a surveyor, canal builder, and amateur geologist from England.
• 1851 - Smith


  Smith produced a geologic map of England in which he successfully demonstrated the validity of the principle of faunal succession.
• validity of the principle of faunal succession.


  t fossils are found in rocks in a very definite order.
• The principle of biologic succession

  Each Earth's history is unique, resulting in unique fossil remains, allowing for vertical and horizontal correlation of rock layers based on fossil species.
• Precambrian Eon


  More than 85% of earth's history falls under this supereon, from 4.6 billionyears ago to 540 million years ago.
• Hadean Eon (4.6 bya to 4 bya)


  The solidification of the earth's continental and oceanic crust

  
  

  • solar system was forming within a cloud of dust and gas known as the solar nebula, which eventually spawned asteroids, comets, moons and planets

  
  

  • It was characterized by Earth's formation and it's hellish environment
• Archean Eon (4 Billion Years to 2.5 billion years ago)


  The evolution of earth's first life forms

  • Approximately 70 percent of continental landmass was formed during this time.

  
  

  • Earth had acquired enough mass to hold a reducing atmosphere composed of methane, ammonia and other gases

  
  

  • Water from comets and hydrated minerals condensed in the atmosphere and fell as torrential rain, cooling the planet and filling the first oceans with liquid water.

  
  

  • It is probable that these microscopic prokaryotes began as chemoautotrophs, anaerobic bacteria able to obtain carbon from carbon dioxide (CO2 ).

  
  

  • By the end of the Archean, the ocean floor was covered in a living mat of bacterial life.
• Proterozoic Eon (2.5 Billion Years ago)


  The appearance of multi-celled animals and the gathering of land masses to form continents

  
  

  • About 2.5 billion years ago, enough shield rock had formed to start recognizable geologic processes such as plate tectonics.

  
  

  • About 1.2 billion years ago, plate tectonics forced the available shield rock to collide, forming Rodinia . (Russian term meaning mother land, Earths first continent)

  
  

  • coastal waters were filled with rounded colonies of photosynthetic algae known as stromatolites

  
  

  The appearance of multi-celled animals and the gathering of land masses to form continents

  
  

  • The Ediacaran Period , the last of the Proterozoic Era, saw the first multicellular organisms.

  
  

  • Autotrophs and soft-bodied heterotrophs filled the continental shelf regions around Rodinia

  
  

  • The cnidarians, which included sea anemones, corals, and jellyfish, had sac-like bodies and a simple digestive system with a mouth but no anus. They caught food using tentacles armed with microscopic stinging cells.

  
  

  • Sponges lacking organs or a nervous system, they lived by drawing water through their bodies and filtering out food particles

  
  

  • Annelids or segmented flatworms, had fluid-filled body cavities and breath through their skin
• Paleozoic Era (544 Million Years Ago)


  The explosion of diverse marine life and the largest mass extinction of marine organisms

  
  

  • started with an explosion of multicellular life, called the Cambrian Explosion.

  
  

  • Marine trilobites were common.

  
  

  • The first invertebrates and fish are found, later the first amphibians and insects.

  
  

  • Diverse land plants develop and coal swamps form in certain areas.

  
  

  • The first reptiles form.

  
  

  • This era ended with the massive Permian Extinction, wiping out many successful species
• Eras under Phanerozoic Eon

  Cenozoic Era (65 Million Years ago -Now This is the most recent among the eras of the Phanerozoic Era; this era marks the age of mammals and the first human evolution.

  
  

  Mesozoic Era (245 Million Years Ago) This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction.

  
  

  Paleozoic Era (544 Million Years Ago) The explosion of diverse marine life and the largest mass extinction of marine organisms
• periods under Paleozoic Era

  Permian Period (298.9 MYA)

  
  

  Pennsylvanian Period (323.2 MYA)

  
  

  Mississippian Period (358.9 MYA)

  
  

  Devonian Period (419.2 MYA)

  
  

  Silurian Period (443.8 MYA)

  
  

  Ordovician Period (485.4 MYA)

  
  

  Cambrian Period (541.0 MYA)
• Cambrian Period

  The Paleozoic Era began

  
  

  53 million years best known for ushering in an explosion of life on Earth.

  
  

  • This "Cambrian explosion" included the evolution of arthropods (ancestors of today's insects and crustaceans) and chordates (animals with rudimentary spinal cords).
• Ordovician Period,


  is marked in the fossil record by an abundance of marine invertebrates.

  
  

  • Perhaps the most famous of these invertebrates was the trilobite, an armored arthropod that scuttled around the seafloor for about 270 million years before going extinct
• Silurian Period (443.8 million to 419.2 million years ago),


  saw the spread of jawless fish throughout the seas.

  
  

  • Mollusks and corals also thrived in the oceans, but the big news was what was happening on land: the first undisputed evidence of terrestrial life
• Devonian Period


  the time when plants evolved, though they most likely did not yet have leaves or the vascular tissue that allows modern plants to siphon up water and nutrients.

  
  

  Ferns appeared, as did the first trees. At the same time, the first vertebrates were colonizing the land. These vertebrates were called tetrapods, and they were widely diverse:
• Carboniferous Period


  Long before birds evolved, tetrapods began laying eggs on land for the first time during this period, allowing them to break away from an amphibious lifestyle.

  
  

  • Trilobites were fading as fish became more diverse.

  
  

  • The ancestors of conifers appeared, and dragonflies rues the skies

  
  

  • Tetrapods were becoming more specialized, and two new groups of animals evolved.

  
  

  • The first were marine reptiles, including lizards and snakes.

  
  

  • The second were the archosaurs, which would give rise to crocodiles, dinosaurs and birds.

  
  

  • Most creepily, this era is sometimes referred to as the "Age of the Cockroaches," because roaches' ancient ancestor (Archimylacris eggintoni) was found all across the globe during the Carboniferous.
• two types of archosaur:

  1. Those more closely related to birds (bird-line) called the ornithodirans, which includes dinosaurs and pterosaurs.

  
  

  2. And those more closely related to crocodiles (crocodileline) called the pseudosuchians, which are less popularly known.
• Permian Period

  last period

  
  

  This period would end with the largest mass extinction ever: the Permian extinction.

  
  

  • Before the Permian mass extinction, though, the warm seas teemed with life.

  
  

  • Coral reefs flourished, providing shelter for fish and shelled creatures, such as nautiloids and ammonoids.

  
  

  • Modern conifers and ginkgo trees evolved on land.

  
  

  • Terrestrial vertebrates evolved to become herbivores, taking advantage of the new plant life that had colonized the land.
• Permian Extinction

  characterized by the elimination of about 90 percent of the species on Earth, which included more than 95 percent of the marine species and 70 percent of the terrestrial species.

  
  

  • In addition, more than half of all taxonomic families present at the time disappeared. This event ranks first in severity of the five major extinction episodes that span geologic time.

  
  

  • The Permian extinction was not restricted to marine invertebrates.

  
  

  • Several groups of aquatic vertebrates, such as the acanthodians, thought to be the earliest jawed fishes, and the placoderms, a group of jawed fishes with significant armour, were also eliminated.

  
  

  • Notable terrestrial groups, such as the pelycosaurs (fin-backed reptiles), Moschops (a massive mammal-like reptile), and numerous families of insects also met their demise.

  
  

  • In addition, a number of groups (such as sharks, bony fishes, brachiopods, bryozoans, ammonoids, therapsids, reptiles, and amphibians) experienced significant declines by the end of the Permian Period.
• Causes of Permian Extinction

  1. Temperature crises

  
  

  2. Alteration of the carbon cycle

  
  

  3. Population explosion of methane-producing microbes

  
  

  Other possible causes

  
  

  • assembly of Pangea, a vast north-south supercontinent
• Paleozoic geology and climate

  z• During the Cambrian Period of the Paleozoic, the continents underwent a change.

  
  

  •During the Cambrian Period, Rodinia, once a supercontinent, split into Gondwana and smaller northern continents, forming the modern Southern Hemisphere.

  
  

  • The Cambrian was warm worldwide, but would be followed by an ice age in the Ordovician, which caused glaciers to form, sending sea levels downward.

  
  

  • Gondwana moved further south during the Ordovician, while the smaller continents started to move closer together.

  
  

  • During the Silurian Period, North America, central and northern Europe, and western Europe merged, leading to increased sea levels and shallow inland seas.

  
  

  • Gondwana still existed, but the rest of the planet was ocean. By the last period of the Paleozoic, the Permian, Euramerica and Gondwana became one, forming perhaps the most famous supercontinent of them all: Pangaea.

  
  

  • The giant ocean surrounding Pangaea was called Panthalassa. Pangaea's interior was likely very dry, because its massive size prevented water-bearing rain clouds from penetrating far beyond the coasts
• Periods under Mesozoic Era

  Cretaceous Period (145.0 MYA)

  
  

  Jurassic Period (201.3 MYA)

  
  

  Triassic Period (251.9 MYA)
• Mesozoic Era (245 Million Years Ago)

  This era marks the beginning of dinosaurs, mammals, birds, and plants due to mass extinction.

  
  

  • The Mesozoic era saw the rise of some of the most iconic animals, from Tyrannosaurus rex to birds and mammals.

  
  

  • or "Middle Life" era, life diversified rapidly and giant reptiles, dinosaurs and other monstrous beasts roamed the Earth.

  
  

  • The period, which spans from about 252 million years ago to about 66 million years ago, was also known as the age of reptiles or the age of dinosaurs.
• Life and Climate in Mesozoic Era


  • Life slowly rebounded, eventually giving way to a flourishing diversity of animals, from massive lizards to monstrous dinosaurs

  
  

  • The Triassic period, from 252 million to 200 million years ago, saw the rise of reptiles and the first dinosaurs.

  
  

  • The Jurassic period, from about 200 million to 145 million years ago, ushered in birds and mammals
• Chinese Dragon


  Scientists have discovered fossils of an ancient seaborne "dragon" in China, the "Chinese dragon." The 240 million-year-old animal, part of the Dinocephalosaurus orientalis species, used its long neck to ambush prey in shallow waters during the Triassic period. The species was first discovered in southern China in 2003, and scientists have now reconstruct its full 16.8-foot (5 meters) span for the first time. This discovery has led to the creation of shallow inland seas.
• Triassic Period

  • At the end of the Triassic period, roughly 201 million years ago, most amphibious creatures and crocodile-like creatures that lived in the tropics were wiped out.

  
  

  • Because the fossil record is incomplete, it's difficult to say exactly what caused the extinctions, or even how rapidly they occurred.

  
  

  • After all, certain species or traces of catastrophic events could be missing in the fossil record simply because the sediments may have disappeared over tens of millions of years.