Wednesday, July 06, 2011

Working with extinct animals: Basics (3): dates and continents

What is relative dating? Absolute dating? Give examples of each.
Rocks in the lower layers of strata are usually older than the ones on top, therefore geologists can begin estimating the dates for each layer of strata. Also with William Smith’s “Principle of Faunal Succession”, geologists can determine the relative ages of rock layers. (This principle means that fossils succeed each other vertically in a specific order.)  By comparing various fossils of different rocks, they can tell if the rocks are from the same or different times.  Also through the use of fossils, geologists can determine the various ages contained in the rock strata.  They often do this with index fossils such as trilobites, which are abundant, easily identifiable, and lived in a known environment. 

In order to tell the actual date of a rock, geologists use absolute dating.  Various elements decay at different rates.  For example, when first formed uranium starts to decay.  (Lead is the end product of uranium.) Because of this, geologists use radioactive elements in rocks to date their true age.  Since igneous rocks have radioactive elements, they are the ones used in absolute dating.  Because of their composition (mostly mud and silt), sedimentary rocks are useless for this type of dating.

What are the names of the early continents? What causes the break-up and formation of continents?
The earth’s continents are like dumplings floating in a soup.  The continents are lighter plates of granite floating on heavier basalt rocks.  When these plates drift apart or together, continents are formed and reformed.  Meanwhile, the oceanic crust is both thinner and denser than the continental crust.  Because the oceanic crust is more active, the sea floor spreads, thereby pushing continents together.  When two plates collide, mountains are formed.  When oceanic plates collide, one pushes under the other forming volcanoes such as the ones in Hawai’i.  Meanwhile, other continental plates move sideways creating friction, and eventually causing earthquakes.

SUPEREON: Precambrian (Cryptozoic)
EON: Hadean

EON: Archean
Kenorland, Ur, Vaalbara

EON: Proterozoic
Arctica, Atlantica, Nena, Rodinia

SUPEREON: Cambrian
EON: Phanerozoic

ERA: Paleozoic
PERIOD: Cambrian, Ordovician, Silurian
Baltica (Europe), Laurentia (North America), Gondwana
PERIOD: Devonian, Carboniferous
Euroamerica (Baltic and Laurentia), Gondwana
PERIOD: Permian
Pangea (Euroamerica and Gondwana)

ERA: Mesozoic
PERIOD: Triassic
PERIOD: Jurassic
Antarctica, Gondwana, Laurasia
PERIOD: Cretaceous
Africa, Antarctica and Australia, Eurasia, North America, South America

ERA: Cenozoic
PERIOD:  Paleogene (or Tertiary)
Africa, Antarctica, Asia, Australia, Europe, North America, South America
PERIOD: Neogene, Quaternary
Africa, Antarctica, Australia, Eurasia, North America, South America


Evolutionist, “Paleogeology Blog”,, 2009, .

Geological Society of America, “2009 Geologic Time Scale”,, .

Little, Richard, “Dinosaurs, Dunes, and Drafting Continents: the Geohistory of the Connecticut Valley”, self-published, Hartford, CT, 1986.

Pianka, Eric and Laurie Vitt, “Lizards: Windows to the Evolution of Diversity”, University of California, Berkeley, 2003.

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