Prehistoric times

Contents:

• Geologic time - an overview
• Hadean eon: 4,600-3,900 mya - solidification of earth's crust
  • Cryptic epoch
  • Basin Groups 1-9
  • Nectarian epoch
  • Early Imbrian epoch
• Archeozoic eon: 3,900-2,500 mya - bacteria, blue-green algae & archaens start to oxygenate atmosphere
  • Isuan era
  • Swazian era
  • Randian era
• Proterozoic eon (2500 - 540 mya):
  • early period - multi-celled organisms, soft-bodied invertebrates further oxygenate atmosphere
  • Pre-Cambrian:
  • Huronian era
  • Animikean era
  • Riphean era
  • Sinian era
    • Sturtian period
    • Vendian period - algae, Ediacaran soft-bodied fauna
• Phanerozoic "obvious life" eon:
  • Paleozoic era:
    • Cambrian period - marine invertebrates (snails, trilobites), seaweed, lichen
    • Ordovician period - marine vertebrates (fish), coral
    • Silurian period - air-breathing animal, land plants
    • Devonian period - amphibia, insects, woody plants (ferns, scale trees, forests)
    • Carboniferous period - spiders, cockroaches, reptiles, conifers
    • Permian period - disappearance of many marine forms including the trilobites, rapid evolution of reptiles
  • Mesozoic era: "age of the reptiles"
    • Triassic period - mammals, dinosaurs, turtles
    • Jurassic period - more dinosaurs & reptiles, birds, moth, fly, beetle, grasshopper, termite, lobster, shrimp
    • Cretaceous period - marsupials, placental mammals, crabs, deciduous trees, flowering plants, disappearance of dinosaurs
  • Cenozoic era: "age of the mammals"
    • Tertiary period:
      • Paleogene:
        • Paleocene epoch - small mammals
        • Eocene epoch - horse, rhinoceros, camel, rodent, monkey, modern birds, aquatic mammals
        • Oligocene epoch - first true carnivore mammals, first anthropoid apes
      • Neogene:
        • Miocene epoch - mastodon, grasses
        • Pliocene epoch - higher mammals
    • Quaternary period:
      • Pleistocene epoch: - ice age, "age of man"
        • Paleolithic - old stone age
      • Holocene epoch: - recent times
        • Neolithic - new stone age
• see also:
  • Main Page
  • ancient history
  • Glossary
  • history of the sun
    • http://www.americanscientist.org/template/AssetDetail/assetid/21173/page/2 
    • sun orbits the galactic centre once every 250 million years

Geologic time - an overview:

• Geologic time has been divided into parts and sub-parts as follows:
  • eon
    • era
      • period
        • sub-period
          • epoch
            • age

Pre-Cambrian or Cryptozoic ("hidden life") Eon:

• 600-6000 million yrs ago
• earth formed (~6,000 million yrs ago???)
• earth spun more rapidly on its axis so a day was only 4-5 hours and the moon was much closer, while giant meteorites impacted earth - the only constant environment was the deep ocean floor protected from UV radiation with little variation in temperature or pH which allowed life to begin, catalysed by minerals which would form the basis of many enzymes.
• procaryotic cells (~4,650 million yrs ago)
• eucaryotic cells (~3,500 million yrs ago
• algae life forms (~1,500 million yrs ago)
• neoproterozoic: at least 4 extreme climate reversals from global ice to hot house effect of carbon dioxide (750-580 million years ago):
  • the more of earth covered by ice, the more the sun's heat is reflected making the earth colder still and creating more ice
  • but the more ice there is, the less liquid water there is to convert carbon dioxide from volcanic activity to carbonates, thereby eventually creating a greenhouse effect which reverses an ice age if atmosphere levels reach 350x current levels, this would take tens of millions of years of volcanic activity. The greenhouse effect (further assisted by greenhouse effect of increasing water vapour) would drive surface temperatures to almost 50deg C !!
  • rain would then decrease atmospheric carbon dioxide levels creating seawater highly saturated in calcium carbonate
• The first abundant fossils date from about 600 million years ago. The reason for the scarcity of earlier fossils is not fully understood, but in Precambrian times most species of animals probably were soft-bodied, and shells and other hard body parts suitable for preservation did not develop until the Cambrian period.
• Ediacaran fauna, distinctive grouping of fossils dating from and existing only during Precambrian time. The fauna arose about 670 million years ago and is named for Australia's Ediacara hills, where it was first discovered. Such fossils were later found to be widespread. Ranging up to about 1 m (about 3 ft) long, the animals lived in shallow seas and had soft bodies that bear little resemblance to later life forms. Conceivably they may represent an early, extinct branch in the evolutionary history of animals

Three great eras of the Phanerozoic ("obvious life") eon:

Paleozoic "ancient life" era:

• 230-600 million yrs ago
  • Cambrian period:
    • 500-600 million yrs ago
    • Multiple collisions between the earth's crustal plates gave rise to the first supercontinent, known as Gondwanaland.
    • Animal life was entirely confined to the seas - marine invertebrates
    • With the exception of the vertebrates, all the phyla of the animal kingdom existed by the end of the Cambrian times:
      • 1st branching:
        • poriferans
        • 2nd branching:
          • cnidarians
          • 3rd branching:
            • 4th branching:
              • echinoderms
              • chordates
            • 5th branching:
              • 6th branching:
                • brachiopods
                • later branching:
                  • platyhelminths
                  • futher branching:
                    • annelids
                    • mollusks
              • 7th branching:
                • priapulids
                • further branching:
                  • nematodes
                  • arthropods
    • The characteristic animals of the Cambrian period were the trilobites, a primitive form of arthropod, which reached their fullest development in this period and became extinct in Permian times.
    • Among the mollusks, the earliest snails appeared in this period, as did the cephalopod mollusks.
    • Flora was entirely confined to such low forms as seaweeds in the oceans and lichens on land.
  • Ordovician period:
    • 425-500 million yrs ago
    • The predecessor of today's Atlantic Ocean began to shrink as the continents of that time drifted closer together.
    • The most characteristic animals of this period were the graptolites, which were small, colonial coelenterates.
    • The first vertebrates (marine vertebrates - primitive fishes) and the earliest corals emerged.
    • The largest animal was a cephalopod mollusk that had a shell about 3 m (about 10 ft) in length.
    • Flora resembled that of the Cambrian period.
  • Silurian period:
    • 405-425 million yrs ago
    • The most important evolutionary development of this period was the first air-breathing animal, a scorpion.
    • The first fossil records of vascular plants, that is, land plants with conducting tissue, appeared. They were simple plants without differentiation into stem and leaf.
  • Devonian period:
    • 345-405 million yrs ago
    • "Age of the fishes"
    • The dominant forms of animal life were fish of various types, including shark, lungfish, armored fish, and primitive forms of ganoid (hard-scaled) fish that are believed to have been the evolutionary ancestor of the amphibians.
    • Fossil remains found in Pennsylvania and Greenland indicate that early forms of amphibia may already have existed during the period.
    • Lower animal forms included coral, starfish, sponge, and trilobite.
    • The earliest known insect was found in Devonian rock.
    • The Devonian is the first period from which any considerable number of fossilized plants has been preserved.
      • During this period, the first woody plants developed, and before the period had closed, the land-growing forms included seed ferns, ferns, scouring rushes, and scale trees, the modern relative of which is club moss. Although the present-day equivalents of these groups are mostly small plants, they developed into treelike forms in the Devonian period.
      • Fossil evidence indicates that forests existed in Devonian times, and petrified stumps of certain of the larger plants from the Devonian period are 60 cm (24 in) in diameter.
  • Carboniferous period:
    • 280-345 million yrs ago
    • named after the numerous coal beds which resulted from warm, humid climates which fostered lush forests in swamplands
    • first part of this period, known as the Mississippian in US geology:
      • A group of sharks, the Cestraciontes or shell-crushers, were dominant among the larger marine animals.
      • The predominant group of land animals was the Stegocephalia, an order of primitive, lizardlike amphibians that developed from the lungfish.
      • The various forms of land plants became diversified and grew larger, particularly those that grew in low-lying swampy areas.
    • second part - known as the Pennsylvanian in U.S. geology:
      • evolution of the first reptiles, a group that developed from the amphibians and that was completely independent of a water environment.
      • other land animals included spiders, snails, scorpions, more than 800 species of cockroach, and the largest insect ever evolved, a species resembling the dragonfly, with a wingspread of about 74 cm (about 29 in).
      • The largest plants were the scale trees, the tapered trunks of which were as much as 1.8 m (6 ft) in diameter at the base and 30 cm (100 ft) high. Primitive gymnosperms known as cordaites, which had pithy stems surrounded by a woody shell, were more slender but even taller.
      • The first true conifers developed - advanced gymnosperms.
  • Permian period:
    • 230-280 million yrs ago
    • The earth's land areas became welded into a single landmass that geologists call Pangaea, and in the North American region the Appalachian Mountains were formed.
    • The chief features of the animal life were the disappearance of many forms of marine animals and the rapid spread and evolution of the reptiles.
    • In general, reptiles were of two types:
      • lizardlike reptiles that lived wholly on land
      • sluggish, semiaquatic types.
    • a comparatively small group of reptiles that evolved in this period, the Theriodontia, was the group from which the mammals later developed.
    • the predominant vegetation was composed of ferns and conifers.
    • it is now thought by many that the end of the Permian age 250m yrs ago (ie. before dinosaurs) was due to a NEO which hit earth and plunged earth into darkness & freezing cold, caused volcanoes & released hydrogen sulphide gas, wiping out 90% of sea life & 80% of land life globally - the "Great Dying" in addition to setting off the separation of the continents from the unified Gondwana land mass a 150m yrs later. The possible sites are either:
      • Wilkes land region of east Antartica - 483km wide crater hidden more than 1.6km beneath the Antartic ice sheet and has a 321km wide plug of mantle - a mascon. The rift between Antartica and Australia passes directly through this crater. (published 2006)
      • offshore from NW of Western Australia when it was part of Pangaea resulting in the Bedout High underwater crater which is buried beneath thousands of metres of rock (discovered by oil drilling samples). The meteor is estimated to have been at least 10km diameter, leaving an impact crater of 200km diameter.

Mesozoic "middle life" era:

• 65-230 million yrs ago
  • Triassic period:
    • 181-230 million yrs ago
    • the reappearance of Gondwanaland, as the supercontinent, Pangaea, split apart into northern (Laurasia) and southern (Gondwanaland) supercontinents after the early dinosaurs has established themselves.
    • mammals, more reptiles such as turtles
    • early dinosaurs seldom exceeded 4.5m in length
    • first ancestors of the modern bony fishes, Teleostei, made their appearance
    • the dominant vegetation was composed of various evergreens, such as ginko, conifer, and palm. Small scouring rushes and ferns continued to exist, but the larger members of these groups had now become completely extinct.
  • Jurassic period:
    • 135-181 million yrs ago
    • As Gondwanaland rifted apart, the North Atlantic Ocean widened and the South Atlantic was born.
    • dinosaurs:
      • four distinct types, or tribes:
        • heavy four-footed sauropods, such as Apatosaurus;
        • two-footed carnivorous dinosaurs such as Tyrannosaurus;
        • two-footed vegetarian dinosaurs such as Trachodon;
        • four-footed armored dinosaurs, such as Stegosaurus.
    • marine reptiles included:
      • plesiosaurs, a group that had broad, flat bodies like those of turtles, with long necks and large flippers for swimming;
      • ichthyosaurs, which had scaly bodies;
      • primitive crocodiles
    • winged reptiles were represented by Pterosaurus, popularly referred to as pterodactyl
    • The earliest confirmed fossil identified as a bird, Archaeopteryx lithographica, is from the Late Jurassic
    • evolution of the insects resulted in the development of a number of the modern orders, including moth, fly, beetle, grasshopper, and termite.
    • Shellfish included lobster, shrimp, and ammonite, as well as the extinct group of belemnites that resembled squid and had cigar-shaped internal shells.
    • The flora of the Jurassic period was dominated by the cycad.
  • Cretaceous period:
    • 65-135 million yrs ago
    • The Rocky Mountains began to rise in North America
    • other mammals evolved: 1st marsupials, 1st placental mammals
    • other shellfish evolved: crabs
    • several modern varieties of fish evolved
    • ants evolve into two main subfamilies 80-100mya in association with the rise in forest ground litter and soil associated with flowering plants (angiosperms):
      • Sphecomyrminae - now extinct
      • precursor of modern ants which during this period evolved into subfamilies including:
        • Myrmiciinae - genus Myrmecia - jumper ants and bull dog ants (only survived in Australia)
        • Myrmicinae - 
        • Formicinae -
        • Ponerinae 
        • Dolichoderinae - includes the invasive Argentine ant which now has a super-colony 100km wide under Melbourne, Australia
    • fifth tribe of dinosaurs evolved such as horned dinosaurs-Triceratops
    • 74mya, ice-free polar regions, mild climates, seas at full flood separated:
      • the North American continent into sections via the north-south running "Western Interior Seaway" along the east of the Rocky Mountains which covered Nebraska, Kansas, Texas & the "Hudson Seaway" separating Ontario, Qebec & Newfoundland in the south from the "Northwest territories" which were themselves separated from Greenland by the "Labrador Seaway"
      • North Atlantic flooded south-eastern USA up to near the Appalachian Mountains
      • Asia from Europe
    • by end of this period, all dinosaurs became extinct - probably as a result of a NEO of 15km diameter (100 million megatons energy) hitting Chicxulub on Mexico's Yucatan peninsula
    • development of deciduous and flowering plants (angiosperms):
      • fig, magnolia, sassafras, and poplar were among the earliest to evolve.
      • mid-Cretaceous fossils include remains of beech, holly, laurel, maple, oak, plane tree, and walnut.
      • by the end of the period, many of the modern varieties of trees and shrubs had made their appearance; they represented more than 90 percent of the known plants of the period. Some paleontologists believe that these deciduous woody plants first evolved in Jurassic times but grew only in upland areas, where conditions were unfavorable for fossil preservation.

Cenozoic "recent life" era:

• 65million yrs ago to today - the "age of the mammals"
• Tertiary period:
  • North America's land link to Europe was broken, but its ties to South America were forged toward the end of the period.
  • Paleogene:
    • Paleocene epoch:
      • 54-65 million yrs ago
      • 7 groups of 4-footed, 5-toed, small mammals originating in Nth Asia:
        • only 4 groups survived:
          • marsupials
          • insectivores
          • primates
          • rodents
        • the 3 groups that became extinct are:
          • the creodonts, which were the ancestors of the modern carnivores;
          • the amblypods, which were small, heavy-bodied animals;
          • the condylarths, which were light-bodied herbivorous animals with small brains.
    • Eocene epoch:
      • 38-54 million years ago
      • a number of direct evolutionary ancestors of modern animals appeared:
        • Among these animals, all of which were small in stature, were the horse, rhinoceros, camel, rodent, and monkey.
        • The creodonts and amblypods continued to develop during the epoch, but the condylarths became extinct before its close.
        • The first aquatic mammals, the ancestors of the modern whales
        • modern birds as eagle, pelican, quail, and vulture.
      • In these times and continuing to the present, the changes in vegetation were chiefly in the migration of vegetation types in response to climate changes.
    • Oligocene epoch:
      • 26-38 million years ago
      • most of the archaic mammals disappeared to be replaced by modern mammals
      • first true carnivores, resembling dogs and cats, evolved
      • The first anthropoid apes, but they became extinct in North America during the epoch.
      • Two extinct groups of animals flourished during the Oligocene epoch:
        • the titanotheres, which are related to the rhinoceros and the horse;
        • the oreodonts, which are small, doglike, grazing animals
  • Neogene:
    • Miocene epoch:
      • 12-26 million years ago
      • the first appearance of the grasses. These plants, which were ideally suited for forage, encouraged the growth and development of grazing animals such as horse, camel, and rhinoceros, which were abundant during the epoch.
      • the mastodon evolved, and in Europe and Asia a gorillalike ape, Dryopithecus, was common.
      • Various types of carnivores, including cats and wolf-like dogs, ranged over many parts of the world.
    • Pliocene epoch:
      • 2.5-12 million yrs ago
      • higher mammals
      • western Victorian volcanic activity
      • ~5mya - a nearby star (within 90 light years) goes supernova sprinkling Earth with a thin layer of Fe60, an iron isotope produced only by supernova detonations, and many UV-sensitive marine plants and animals died.
• Quaternary period:
  • Pleistocene epoch:
    • 10,000-2.5 million yrs ago
    • the ice age:
      • spreading of glacier ice over more than one-fourth of the land surface of the earth
      • while snow and ice accumulated in higher latitudes, rainfall increased in the lower latitudes, allowing plant and animal life to flourish in areas of northern and eastern Africa that have since become arid and barren.
    • emergence of humans thus the "Age of man", large mammals
    • In Europe:
      • antelope, lion, and hippopotamus appeared.
      • carnivores included badger, fox, lynx, otter, puma, and skunk, as well as now-extinct species as the giant saber-toothed tiger
    • In Nth America:
      • buffalo, elephant, mammoth, and mastodon appeared, however the mammoth and mastodon became extinct towards end of this epoch.
      • the first bears made their appearance as migrants from Asia
      • The armadillo and ground sloth migrated from South America
      • many species of mammals became extinct in North America, including the llama, camel, tapir, horse, and yak
    • Paleolithic "old stone age":
      • 10,000-1,000,000 yrs ago
      • beryllium-10 spikes at 33,000 and 60,000 yrs ago suggest possible nearby supernovas causing dramatic rise in cosmic ray flux.
      • migration of humans across continents
        • humans crossed over into the New World by means of the Bering land bridge.
  • Holocene epoch "Recent times":
    • present - 10,000 yrs ago
    • Neolithic "new stone age":
      • 4,000 - 10,000 yrs ago
      • melting ice caused the sea level to rise a hundred feet or more, drowning large areas of land and broadening the continental shelf of eastern North America, isolating regions from each other such as:
        • Britain from Europe
        • Tasmania from mainland Australia
      • agriculture, domesticated animals
    • Written history:
      • present - 4,000 yrs ago