<P> During the Cretaceous, the late Paleozoic - early Mesozoic supercontinent of Pangaea completed its breakup into present day continents, although their positions were substantially different at the time . As the Atlantic Ocean widened, the convergent - margin orogenies that had begun during the Jurassic continued in the North American Cordillera, as the Nevadan orogeny was followed by the Sevier and Laramide orogenies . Though Gondwana was still intact in the beginning of the Cretaceous, Gondwana itself broke up as South America, Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached to each other); thus, the South Atlantic and Indian Oceans were newly formed . Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide . </P> <P> To the north of Africa the Tethys Sea continued to narrow . Broad shallow seas advanced across central North America (the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds . At the peak of the Cretaceous transgression, one - third of Earth's present land area was submerged . The Cretaceous is justly famous for its chalk; indeed, more chalk formed in the Cretaceous than in any other period in the Phanerozoic . Mid-ocean ridge activity--or rather, the circulation of seawater through the enlarged ridges--enriched the oceans in calcium; this made the oceans more saturated, as well as increased the bioavailability of the element for calcareous nanoplankton . These widespread carbonates and other sedimentary deposits make the Cretaceous rock record especially fine . Famous formations from North America include the rich marine fossils of Kansas's Smoky Hill Chalk Member and the terrestrial fauna of the late Cretaceous Hell Creek Formation . Other important Cretaceous exposures occur in Europe and China . In the area that is now India, massive lava beds called the Deccan Traps were laid down in the very late Cretaceous and early Paleocene . </P> <P> The Cenozoic Era covers the 66 million years since the Cretaceous--Paleogene extinction event up to and including the present day . By the end of the Mesozoic era, the continents had rifted into nearly their present form . Laurasia became North America and Eurasia, while Gondwana split into South America, Africa, Australia, Antarctica and the Indian subcontinent, which collided with the Asian plate . This impact gave rise to the Himalayas . The Tethys Sea, which had separated the northern continents from Africa and India, began to close up, forming the Mediterranean sea . </P> <P> The Paleogene (alternatively Palaeogene) Period is a unit of geologic time that began 66 and ended 23.03 Ma and comprises the first part of the Cenozoic Era . This period consists of the Paleocene, Eocene and Oligocene Epochs . </P>

During which geologic era did earth’s continents come to their approximate present-day locations