an emergent
website design
by
peter jay stein, md, ma
atmosphere
asthenosphere
lithosphere
regolith
biosphere
hydrosphere
This 54 page synopsis of the evolution
of the Earth, the origin and progression of life, and the
emergence of humans as descendants of the hominin lineage, divides the last 4.57 billion years into progressively overlapping, imagistic, time segments, to outline our place in biological existence.
magnetosphere
ionosphere
FORTY-TWO
Emergent Cretaceous Period: 145 - 66 mya
Features of the Cretaceous Period: 145 - 66 mya
1) This is the 3rd, and last period of the Mesozoic (Age of Reptiles) era, which ends with a mass extinction event, eliminating all dinosaurs, and other animals weighing above 50 lbs. (25 kg). This period is the longest of the Phanerozoic Eon, spanning 79 million years.
3) The flowering plants, or angiosperms, arrived and began to diversify about 130 mya (as did the hardwood trees and grasses), whereby animals more efficiently deliver pollen (rather than wind-driven pollen), the animals attracted to both the color and scent of the flowers. Prior to the arrival of the angiosperms, were the gymnosperms.
4) A second radiation of insects appear, including butterflies, moths, ants, and bees, many of which drank flower nectar, and developed complex colonies.
2) The cause of this great extinction is thought to be due to an impact of a 6 mile high (10 km) asteroid, that struck the Earth on the Yucatan Peninsula in Mexico 65-66 mya, the Chicxulub crater discovered in 1991. High concentrations of meteoritic-derivied iridium residues are consistently found in sediments around the world, the stratigraphy of which coincides with such an event.
5) Mosasaurs, now extinct, were large, voracious, marine predators during the Late Cretaceous, over 30 feet in length.
6) The name "Cretaceous" is a Latin derivative of "chalk", for this is the period in geologic time when most chalks were deposited. "..,Chalk is a soft, fine-grained type of limestone composed predominantly of the armourlike plates of coccolithophores, tiny floating algae that flourished during the Cretaceous..." (Britannica.com - Cretaceous Period, Geochronology).
6) The Earth's land masses were comprised of 2 supercontinents, northern Laurasia and southern Gondwana, almost completely separated by the Tethys Sea. With a warmer climate than today, from seafloor volcanic activity, the polar regions had not ice, but forests; dinosaurs roamed Antarctica (Britannica.com)
7) Duck-billed dinosaurs (hadrosaurs), horned dinosaurs (Triceratops), giant marine reptiles (ichthysaurs, mosasaurs, and plesiosaurs), and flying reptiles (pterosaurs) were common, prior to the massive extinction event.
8) Enlargement of mid-oceanic ridges created sea levels up to 800 feet higher than today, as ocean water was pushed from ocean basins, creating shallow seas across the continents (Britannica.com)
9) Over 50% of the world's petroleum reserves were formed during the Cretaceous period, almost 75% forming in the Persian Gulf region, and the remainder forming between the Gulf of Mexico and Venezuela, due to the collection and deposition of organic matter along the margins of the Tethys seaway.