Cretaceous Period: Recovery After Extinction, Pangaea Drifting Apart

The Cretaceous Period ran from around a hundred and forty-five million to sixty-six million years prior. During this era, life on Earth started to recoup from the minor termination occasion of the past period. Moreover, it was a period when the supercontinent Pangaea kept drifting apart. With time, the mainlands started to draw nearer to their advanced positions and Africa had taken its distinctive shape, as did South America. Nonetheless, there were continental differences, as well. Australia was still a constituent of Antarctica and India had not yet slammed into Asia. The most exciting changes, nevertheless, was evolution and how it changed life during this period.

During this time, mammals continued to evolve. However, they remained small, which is not astonishing since archosaurian reptiles - mainly dinosaurs - were widespread and would have eaten up any mammalian animal which couldn't run and stow away. Some of these mammals comprise of the Deltatheroida, Schowalteria, and Zhelestidae among others. At the start of this era, Pterosaurs were predominant yet for some unclear reason started to decrease as the period advanced. Insects began to build their numbers and diversify as well. Examples included termites, ants, moth-like bugs called Lepidopterans, wasps, grasshoppers, and honey bees.

Flowering plants also started to adjust and spread amid the Cretaceous Period. As the bees continued to evolve, a wide range of Angiosperms started to multiple They include figs, magnolias, green trees, and monkey bewilder trees. On the other hand, not all vegetation species were useful during this time. During this time, there was a decrease in Bennettitales and Hirmerellan Conifers until they eventually died out. During the Cretaceous era, Marine fauna also diversified. There was an assortment of marine reptiles present, such as ichthyosaurs and mosasaurs. Additionally, present day sharks and rays became common as did starfish and other types of echinoderms.

During the Jurassic era, the Earth had started cooling, and this pattern continued all through the first age of this period. Higher altitudes brought about snow, and the tropics presumably observed a lot of precipitation. Conversely, by the end of the Early Cretaceous Epoch, global temperatures began rising once again.

During this period, life continued to thrive until the K-T Extinction Event (presently getting to be known as the K-PG Extinction Event. A massive object slammed into the Earth wiping out about seventy-five percent of the world's species. Animals such as ammonites and freshwater mussels were either wiped out eventually to or endured devastating setbacks CITATION Dou19 \l 1033 (Preston). On the other hand, insectivores and scavengers survived this incident, mammals and birds included. Furthermore, Champsosaurs and crocodiles also survived during this occasion since they are semi-aquatic and could live off food from waterways.

This mass destruction opened up a few biological niches however it took quite some time for these niches to get full thanks to the annihilation of the incident. Nonetheless, life did, in the long run, recoup and continue to flourish into the Tertiary Period.

The Fauna

During the Cretaceous era, more primordial birds took off and joined the pterosaurs in the air. Many experts contest the origin of take-off. According to the "trees down" concept, it is believed that small reptiles may have advanced from gliding actions (Bagley). According to the "ground up" theory flight may have advanced from the ability of small theropods to leaping high in a mid to hold its prey. Feathers possibly evolved from ancient body coverings whose primary function was thermoregulation.

It is evident that avians were highly fruitful and became widely spread during the Cretaceous period. Confuciusornis (a hundred and twenty-five million to a hundred and forty million years ago) was a crow-sized bird with a sharp beak, but massive talons at the tips of its wings (Khosla and Lucas 45). Iberomesornis, a modern, and the size of a sparrow could fly and was an insectivore. As the Jurassic period came to an end, some of the enormous dinosaurs, such as Apatosaurus and Diplodocus, eventually died out. However other giant dinosaurs such as the titanosaurs, thrived, particularly toward the end of the Cretaceous period.

Vast herds of herbivorous dinosaurs also flourished during the Cretaceous era. Examples include the Iguanodon (a species that comprises of duck-billed dinosaurs, also called hadrosaurs), and the ceratopsians (Fletcher, Moss, and Salisbury). Theropods, the most diverse group of dinosaurs including Tyrannosaurus rex, continued as top hunters until the Cretaceous period came to an end.

K-Pg extinction incident

About sixty-five million years ago, virtually all big vertebrates and many tropical invertebrates were wiped out in what was a geographical, climatic and biological occurrence with global consequences. Geologists termed it the K-Pg extinction period since it marks the margin between the Cretaceous and Paleogene era. The incident was officially known as the Cretaceous-Tertiary (K-T) event where the letter "K" is derived from a German word for Cretaceous, Kreide.

In 1979, a scientist spotted a thin layer of grey clay separating the Cretaceous and the Paleogene periods. Other geologists found this grey layer widely spread, and tests revealed that it contained high levels of iridium, a component that is uncommon on Earth but found in most meteorites.

Similarly, within this grey layer are signs of "shocked quartz" and small glass-like balls known as tektites that form when a rock suddenly vaporizes then cools down immediately, as it happens when a celestial object strikes the surface of the Earth with great magnitude.

Figure 1.1. A sample of tektites CITATION ACa13 \l 1033 (A Cause for the Cretaceous-Tertiary Mass Extinction event)When the asteroid struck the Earth's surface, its impact prompted shockwaves, huge tsunamis and sent a massive cloud of hot rock and dust into the air. As the hot fragments fell back to Earth, they caused forest fires and very high temperatures.

As such, the torrents of heated dust led to an increase in global temperatures for extended periods after the impact. Also, animals that were too big to seek shelter were heated in the long run. Small animals that could live underground or perhaps in caves or substantial tree trunks, may have survived this heat blast.

The Flora

There was a wide variety of trees in the Cretaceous period. A majority of the trees in that era were of two species, namely angiosperms and gymnosperms.

Angiosperms

Angiosperms are also called flowering plants. They initially came to be, in the lower Cretaceous period that occurred about 125 million years ago. They, however, did not evolve until after about 20 million years, creeping into the Middle Cretaceous era. These early angiosperms had not developed any treelike or shrub-like features up until the end of the Cretaceous periodCITATION Smi11 \l 1033 (Smith). At that point, most of the flowering plants had developed some recognizable features for modern geologists and botanists to recognize and classify. The angiosperms favored areas with damp climates, such as riparian areas, and areas frequented by cycads. It was not until the end of the Cretaceous era that most angiosperms invaded the high latitudes of the south. The angiosperms in the early Cretaceous age were heavily reliant on pollination to further their reach throughout the earth. The angiosperms developed leaves that had more stomata thus smaller, and various vein networks that encouraged higher levels of photosynthesis and transpiration. Coleopteran beetles mainly aided pollination. This partnership between beetles and angiosperms let to a productive diversification of both organisms. This diversification led to a rapid increase in angiosperm productivity that resulted in the rise of angiosperm-dominated forests. These newly risen forests provided abundant food and ecological niches for newer organisms that further encouraged pollination and further spread of angiosperms

Gymnosperms

Gymnosperms are also termed as non-flowering plants. They are characterized mainly by ferns and conifers. The late Cretaceous period heralded the survival of the gymnosperms. This was aided primarily by the rise of the real Cycadales organisms. During this time, there was a replacement of the dominant genera of the gymnosperm organisms. The gymnosperms were mainly dominant in the far north since most of the land had been invaded by the flowering angiosperms that grew at a much faster rate than the gymnosperms CITATION Wag09 \l 1033 (Wageningen University and Research Centre). The Cretaceous period saw a considerable decline in the growth and spread of gymnosperms. Owing to the nature of reproduction, gymnosperms were slow and hard to breakdown. The Cretaceous period saw a lot of unrest resulting from fires, storms, and earthquakes that destroyed most of the Cretaceous era gymnosperms. Before their extinction in most areas of the earth, the gymnosperms covered mainly dry, low level, low nutrient areas. The remnant gymnosperms carried onto the early Cretaceous era without having evolved much.

Abiotic Factors

Climate; Temperatures

The Cretaceous period had a warm, stable environment. At the time, about 130 million years ago, the temperatures at the tropics and the polar region were much higher as compared to today, with no visible ice caps as is seen today CITATION Pik18 \l 1033 (Pika). High temperatures moved to the poles, therefore, preventing the formation of ice sheets that would have made the poles colder. The higher temperatures were a result of a lower gradient between the poles and the equator. This low gradient allowed for hot winds to be easily carried globally. The movement of warm breezes was made more accessible by the fact that the split of Pangea had just started; therefore, most of the land was still close together in one big mass. It was, therefore, more accessible for hot winds to get to various places. Tectonic plates were always moving which resulted in volcanic eruptions. The volcanic eruptions coupled with the tropical winds contributed significantly to the high temperatures experienced during the Cretaceous period.

Climate; Rainfall

The Cretaceous period was characterized by more rainfall than experienced today. This is explained by the relatively warm environment experienced globally. Pangea had just started drifting apart; therefore, most of the earth was dominated by ocean bodies. This meant that evaporation and condensation were occurring on a massive scale. This, thus, resulted in high amounts of rainfall experienced globally but higher amounts at the Equator.

The Soil; Chalk Deposits

The Cretaceous period was characterized by a large number of sea creatures that later died out as a result of the K-Pg extinction event. The skeletons of these marine creatures formed deposits of marine limestone that appears as chalk deposits sedimentation of the skeletal deposits encouraged formation of Cretaceous rocks, these rocks have chalk deposits that are famous throughout northern Europe in places such as White Cliffs of Dover where chalk deposits can be found in the soil from 140 million years ago till date.

A map of the Cretaceous chalk deposits in Europe CITATION Ans13 \l 1033 (Answers In Genesis)

The Soil; Limestone

These types of rocks were formed under warm shallow marine conditions. The stones were mainly as a result of sedimentation of marine coccoliths and skeletons of coccolithophores subjected to extreme pressure over time. This resulted in the presence of Cretaceous limestone in the soil that was later covered up by dust and lava from volcanic eruptions and vegetation from incoming paleontological eras.

Works Cited

"A Cause for the Cretaceous-...