University:
Arizona State University
Course:
ABS 370 | Ecology
Academic year:

2024
Views:

327

Pages:

2
Author:

Thuyoul US

CRETACEOUS HEATING During the Cretaceous, plants and animals were highly productive and ranged practically from pole to pole. The deep ocean waters, which are now near freezing, were about 15 degrees Celsius during the Cretaceous.The average global surface temperature was 10 to 15 degrees warmer than it is today. Conditions were also much warmer in the polar regions, with the temperature difference between the poles and equator only 20 degrees, or about half of today. The continent's shift to warmer equatorial waters may have contributed to much of the mild climate during the Cretaceous. At the time of the initial breakup of the continent about 180 million years ago, the climate began to warm dramatically. Continents are flatter, mountains are lower, and sea levels are higher. Although geography during this time is important, it does not account for all the warming. The continents moved faster than today, with perhaps the most powerful plate tectonics the world has ever known. About 120 million years ago, an incredible explosion of underwater volcanism hit the Pacific Basin. This released a large amount of gaseous lava onto the ocean floor. The volcanic spasms are evidenced by large underwater lava plateau assemblages forming almost simultaneously, the largest, Ontong Java, is about two-thirds the size of Australia. It contains at least 9 million cubic miles of basalt, enough to bury the entire United States under 3 miles of lava. The surge in volcanism increased oceanic crust production by as much as 50 percent. This increase in volcanic activity may have contributed the most to Earth's warming by producing 4 to 8 times the amount of atmospheric carbon dioxide today. As a result, temperatures around the world averaged 7.5 to 12.5 degrees higher than today. Over the next 40 million years, Earth's geomagnetic field, which typically reverses polarity quite often on geologic time scales (Table 10), stabilized. It assumes a constant orientation due to some mantle plumes that produce exceptional basaltic eruptions. This greater volcanic activity increased the carbon dioxide content in the atmosphere, resulting in the warmest global climate in 500 million years. Carbon dioxide also provided an abundant source of carbon for green vegetation and contributed to its remarkable growth, supplying a large diet to herbivorous dinosaurs. The polar forest extends to latitudes 85 degrees north and south of the equator, as shown by the fossil remains of primeval forests that thrived on the now-frozen continent of Antarctica. Evidence of a warm climate supporting lush vegetation is provided by the coal seams flowing through the Transantarctic Mountains, which are among the most extensive coal seams in the world. Alligators and alligators live in high northern latitudes as far north as Labrador, whereas today they are restricted to the warm tropics. Duck-billed hadrasaurs also live in the Arctic and Antarctic regions. The position of the continents may have contributed to climate warming during most of the Mesozoic. Continents clustered together near the equator during the Cretaceous allowing warm ocean currents to carry heat to the poles. High-latitude oceans are less reflective than land. So they absorb more heat, further moderating the climate.