Ordovician period

Examples of Ordovician period in the following topics:

• Bryophytes

  • The first bryophytes (liverworts) probably appeared in the Ordovician period, about 450 million years ago.
  • By the Silurian period, however, vascular plants had spread through the continents.
  • This compelling fact is used as evidence that non-vascular plants must have preceded the Silurian period.
  • Thus, the gametophyte is the dominant and most familiar form; the sporophyte appears for only a short period.

• Evolution of Land Plants

  • The geologic periods of the Paleozoic are marked by changes in the plant life that inhabited the earth.
  • The early era, known as the Paleozoic, is divided into six periods.
  • It starts with the Cambrian period, followed by the Ordovician, Silurian, Devonian, Carboniferous, and Permian.
  • The major event to mark the Ordovician, more than 500 million years ago, was the colonization of land by the ancestors of modern land plants.
  • Fossilized cells, cuticles, and spores of early land plants have been dated as far back as the Ordovician period in the early Paleozoic era.

• The Major Divisions of Land Plants

  • The first vascular plants appeared in the late Ordovician period of the Paleozoic Era (approximately 440-485 million years ago).

• Post-Cambrian Evolution and Mass Extinctions

  • The periods that followed the Cambrian during the Paleozoic Era were marked by further animal evolution and the emergence of many new orders, families, and species.
  • During the Ordovician period, which followed the Cambrian period, plant life first appeared on land.
  • Such periods of mass extinction have occurred repeatedly in the evolutionary record of life, erasing some genetic lines while creating room for others to evolve into the empty niches left behind .
  • The end of the Permian period (and the Paleozoic Era) was marked by the largest mass extinction event in Earth's history, a loss of roughly 95 percent of the extant species at that time.
  • Another mass extinction event occurred at the end of the Cretaceous period, bringing the Mesozoic Era to an end.

• The Cambrian Explosion of Animal Life

  • Echinoderms, mollusks, worms, arthropods, and chordates arose during this period.
  • Unresolved questions about the animal diversification that took place during the Cambrian period remain.
  • For example, we do not understand how the evolution of so many species occurred in such a short period of time.
  • Furthermore, the vast diversification of animal species that appears to have begun during the Cambrian period continued well into the following Ordovician period.
  • These fossils (a–d) belong to trilobites, extinct arthropods that appeared in the early Cambrian period 525 million years ago and disappeared from the fossil record during a mass extinction at the end of the Permian period about 250 million years ago.

• Carbon Dating and Estimating Fossil Age

  • Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is difficult to match up rock beds that are not directly adjacent.
  • For instance, the extinct chordate Eoplacognathus pseudoplanus is thought to have existed during a short range in the Middle Ordovician period.
  • If rocks of unknown age have traces of E. pseudoplanus, they have a mid-Ordovician age.
  • This is difficult for some time periods, however, because of the barriers involved in matching rocks of the same age across continents.

• Biodiversity Change through Geological Time

  • The fossil record of the mass extinctions was the basis for defining periods of geological history, so they typically occur at the transition point between geological periods.
  • The Ordovician-Silurian extinction event is the first-recorded mass extinction and the second largest.
  • The main hypothesis for its cause was a period of glaciation followed by warming.
  • Some researchers have suggested that a gamma-ray burst caused by a nearby supernova is a possible cause of the Ordovician-Silurian extinction.
  • The table shows the time that elapsed between each period.

• Periodic Trends

• The Edo Period

• The Periodic Table of Elements

  • The periodic table is a tabular display of the chemical elements.
  • Groups usually have more significant periodic trends than do periods and blocks, which are explained below.
  • A period is a horizontal row in the periodic table.
  • Here is the complete periodic table with atomic numbers, groups, and periods.
  • Explain how properties of elements vary within groups and across periods in the periodic table