4. MAJOR INTERVALS OF TIME: CHRONOSTRATIGRAPHIC UNITS

    4.1. Precambrian: Fossils extremely rare, consisting of primitive aquatic plants. Evidence of glaciations. Oldest dated algae, over 2,600 my. Oldest dated meteorites: 4,500 my.

        4.1.1. Hadean Eonothem: 4.6 to 3.9 billion years ago. "Rockless Eon" - The solidifying of the Earth's continental and oceanic crusts.

        4.1.2. Archeozoic Eonothem  (Archean):  3.9 to 2.5 billion years ago. "Ancient Life" - The first life forms evolve - one celled organisms. Blue-green algae, archaeans, and bacteria appear in the sea. This begins to free oxygen into the atmosphere.

        4.1.3. Proterozoic Eonothem: 2.5 billion years ago to 540 mya. First multicellular life: colonial algae and soft-bodied invertebrates appear. Oxygen build-up in the Mid-Proterozoic. A mass extinction occurred. The continents had merged into a single supercontinent called Rodinia.

        4.1.3.1. Vendian/Ediacaran System: Vendian biota (Ediacaran fauna) multi-celled animals appear, including sponges. A mass extinction occurred.

    4.2. Phanerozoic Eonothem: "Visible Life" Organisms with skeletons or hard shells. 540 mya through today. 600 to 540 Million Years Ago

        4.2.1 Paleozoic Erathem: "Ancient Life", 540 to 248 mya

            4.2.1.1. Cambrian System: First abundant record of marine life "The Age of Trilobites" 540 to 500 mya
"Age of Trilobites" -The Cambrian Explosion of life occurs; all existent phyla develop. Many marine invertebrates (marine animals with mineralized shells: shell-fish, echinoderms, trilobites, brachiopods, mollusks, primitive graptolites). First vertebrates. Earliest primitive fish. Mild climate. The supercontinent Rodinia began to break into smaller continents (no correspondence to modern-day land masses). Mass extinction of trilobites and nautiloids at end of Cambrian (50% of all animal families went extinct), probably due to glaciation.

            4.2.1.2. Ordovician System: 505 to 438 mya. First fishes, invertebrates dominate. Primitive plants appear on land. First corals. Primitive fishes, seaweed and fungi. Graptolites, bryozoans, gastropods, bivalves, and echinoids. High sea levels at first, global cooling and glaciation, and much volcanism. North America under shallow seas. Ends in huge extinction, due to glaciation.

            4.2.1.3. Silurian System: 438 to 408 mya. First terrestrial plants and animals.
The first jawed fishes and uniramians (like insects, centipedes and millipedes) appeared during the Silurian (over 400 million years ago). First vascular plants (plants with water-conducting tissue as compared with non-vascular plants like mosses) appear on land (Cooksonia is the first known). High seas worldwide. Brachiopods, crinoids, corals.

             4.2.1.4. Devonian System: "The Age of Fishes" 408 to 360 mya. First amphibians, ammonites, fishes abundant.
Fish and land plants become abundant and diverse. First tetrapods appear toward the end of the period. First amphibians appear. First sharks, bony fish, and ammonoids. Many coral reefs, brachiopods, crinoids. New insects, like springtails, appeared. Mass extinction (345 mya) wiped out 30% of all animal families) probably due to glaciation or meteorite impact.

            4.2.1.5. Carboniferous: Wide-spread coal swamps, foraminiferans, corals, bryozoans, brachiopods, blastoids, seed ferns, lycopsids, and other plants. Amphibians become more common. 360 to 280 mya

                4.2.1.5.1. Mississippian Sub-System: 360 to 325 mya: Sharks and amphibians abundant. Large and numerous scale trees and seed ferns.
 First winged insects.

                4.2.1.5.2. Pennsylvanian Sub-System: 325 to 280 mya. Great coal forests, conifers. First reptiles. First reptiles. Many ferns. The first mayflies and cockroaches appear.

            4.2.1.6. Permian System: "The Age of Amphibians" 280 to 248 mya. Mass extinction, most kinds of marine animals, including trilobites. Southern glaciation. "The Age of Amphibians" - Amphibians and reptiles dominant. Gymnosperms dominant plant life. The continents merge into a single super-continent, Pangaea. Phytoplankton and plants oxygenate the Earth's atmosphere to close to modern levels. The first stoneflies, true bugs, beetles, and caddisflies, The Permian ended with largest mass extinction. Trilobites go extinct, as do 50% of all animal families, 95% of all marine species, and many trees, perhaps caused by glaciation or volcanism.

    4.3. Mesozoic -Era Middle Life- "The Age of Reptiles": 248 to 65 mya

        4.3.1. Triassic System: First dinosaurs, abundant cycads and conifers. Triassic Period
248 to 208 mya. The first dinosaurs, mammals, and crocodyloformes appear. Mollusks are the dominant invertebrate. Many reptiles, for example, turtles, i chthyosaurs. True flies appear. Triassic period ends with a minor extinction 213 mya (35% of all animal families die out, including labyrinthodont amphibians, conodonts, and all marine reptiles except ichthyosaurs). This allowed the dinosaurs to expand into many niches.

        4.3.2. Jurassic System: First birds, first mammals, dinosaurs and ammonites abundant. Jurassic Period: 208 to 146 mya. Many dinosaurs, including the giant Sauropods. The first birds appear (Archaeopteryx). The first flowering plants evolve. Many ferns, cycads, gingkos, rushes, conifers, ammonites, and pterosaurs. Minor extinctions at 190 and 160 mya.

        4.3.3. Cretaceous System: 146 to 65 mya: First flowering plants, climax of dinosaurs and ammonites, K/T extinction.

            4.3.3.1. Lower Cretaceous Series: 146-98 mya. The heyday of the dinosaurs. The first crocodilians, and feathered dinosaurs appear. The earliest-known butterflies appear (about 130 million years ago) as well as the earliest-known snakes, ants, and bees. Minor extinctions at 144 and 120 mya.
            4.3.3.2. Upper Cretaceous Series: 98-65 mya. High tectonic and volcanic activity. Primitive marsupials develop. Continents have a modern-day look. Minor extinction 82 mya. Ended with large extinction (the K-T extinction) of dinosaurs, pterosaurs, ammonites, about 50 percent of marine invertebrate species, etc., probably caused by asteroid impact or volcanism.

    4.4. Cenozoic Era -New Life- "The Age of Mammals": 65 mya through today

        4.4.1.Tertiary System:  65 to 1.8 mya

            4.4.1.1. Paleogene Subsystem: 65-24 mya

                4.4.1.1.1. Paleocene Series: 65-54 mya.  First large mammals and primitive primates, plesiadapiforms. First placental mammals.

                4.4.1.1.2. Eocene Series: 54-38 mya. Mammals abound. Rodents appear. Primitive whales appear. Many modern types of mammals

                4.4.1.1.3. Oligocene Series: 38-24 mya. Starts with a minor extinction (36 mya). Many new mammals (pigs, deer, cats, rhinos, tapirs appear). Grasses common. Large running mammals.

            4.4.1.2. Neogene Subsystem: 24-1.8 mya.

                4.4.1.2.1. Miocene Series: 24-5 mya. More mammals, including the horses, dogs and bears. Modern birds. South American monkeys, apes in southern Europe, Ramapithecus. First abundant grazing mammals.

                4.4.1.2.2. Pliocene Series: 5-1.8 mya.  First hominids (australopithecines). Modern forms of whales. Megalodon swam the seas. Large carnivores.

        4.4.2. Quaternary System: "The Age of Man": 1.8 mya to today

            4.4.2.1. Pleistocene Series: 1.8-.011 mya. The Last Ice Age.  Early man, northern glaciation. The first humans (Homo sapiens) evolve. Mammoths, mastodons, saber-toothed cats, giant ground sloths, and other Pleistocene megafauna. A mass extinction of large mammals and many birds happened about 10,000 years ago, probably caused by the end of the last ice age.

            4.4.2.2. Holocene Series: 11,000 ya to today. Modern man. Human civilization.

5. HOW DO WE TELL TIME?
     5.1. Relative time (ages). We are now able to tell geologic time thanks to the scientific contribution of great investigators, among them, Georges Cuvier, Nicholas Steno, William Smith, and James Hutton. They provided a set of principles that are the basis for telling time in fossil-bearing rock and laid down the concepts of Stratigraphy.

    5.2.Fundamental Principles in Geology

        5.2.1. Catastrophism-Creationism
Georges Cuvier (1769-1832). Georges Cuvier's important study Recherches sur les ossemens fossiles des quadrupèdes [Research on the Fossil Bones of Quadrupeds] was first published in France in 1812. The Discours sur les révolutions du globe [Discourse on the Revolutionary Upheavals on the Surface of the Earth] was the introduction to the larger work.
 

5.2.2. Nicholas Steno (1638-1686).  Steno’s contributions to geology was a set of principles still in use, these are: (1) the Principle of Original horizontality; (2) the Principle of Superposition; and (3) the Principle of Lateral continuity

5.2.3. William Smith (1769 –1839).  Smith’s contribution was the Principle of Faunal and floral succession
 

5.2.4. James Hutton (1726-1797).

His major contribution was the book “the history of the Earth”. He added the Principle of Uniformitarianism: The present is the key to the past.
 
 

5.3. Absolute time (ages)
      5.3.1.Radioactivity