Everything about The Mesozoic totally explained
The
Mesozoic Era is one of three
geologic eras of the
Phanerozoic eon. The division of time into eras dates back to
Giovanni Arduino, in the 18th century, although his original name for the era now called the 'Mesozoic' was 'Secondary' (making the modern era the '
Tertiary'). Lying between the
Paleozoic and the
Cenozoic, Mesozoic means 'middle animals', derived from
Greek prefix
meso-/
μεσο- for 'between' and
zoon/
ζωον meaning
animal or 'living being'. It is often called the 'Age of the
Dinosaurs', after the dominant
fauna of the era.
The Mesozoic was a time of
tectonic,
climatic and
evolutionary activity. The continents gradually shifted from a state of connectedness into their present configuration; the drifting provided for
speciation and other important evolutionary developments. The climate was exceptionally warm throughout the period, also playing an important role in the evolution and diversification of new
animal species. By the end of the era, the basis of modern life was in place.
Geologic periods
Following the Paleozoic, the Mesozoic extended roughly 180 million years: from 251 million years ago (
Mya) to when the Cenozoic era began 65 Mya. This time frame is separated into three geologic
periods. From oldest to youngest:
The lower (Triassic) boundary is set by the
Permian-Triassic extinction event, during which approximately 90% to 96% of marine species and 70% of terrestrial vertebrates became
extinct. It is also known as the "Great Dying" because it's considered the largest mass extinction in history. The upper (Cretaceous) boundary is set at the
Cretaceous-Tertiary (KT) extinction event, which may have been caused by the impactor that created
Chicxulub Crater on the
Yucatán Peninsula. Approximately 50% of all genera became extinct, including all of the non-
avian dinosaurs.
Tectonics
Compared to the vigorous convergent plate
mountain-building of the late Paleozoic, Mesozoic tectonic deformation was comparatively mild. Nevertheless, the era featured the dramatic rifting of the
supercontinent Pangaea. Pangaea gradually split into a northern continent,
Laurasia, and a southern continent,
Gondwana. This created the
passive continental margin that characterizes most of the
Atlantic coastline (such as along the
U.S. East Coast) today.
By the end of the 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 during the Cenozoic, the impact giving rise to the
Himalayas.
Climate
The Triassic was generally dry, a trend that began in the late
Carboniferous, and highly seasonal, especially in the interior of Pangaea. Low sea levels may have also exacerbated temperature extremes. With its high
specific heat capacity,
water acts as a temperature-stabilizing heat, and land areas near large bodies of water—especially the
oceans—experience less variation in temperature. Because much of the land that constituted Pangaea was distant from the oceans, temperatures fluctuated greatly, and the interior of Pangaea probably included expansive areas of
desert. Abundant evidence of
red beds and evaporites such as
salt support these conclusions.
Sea levels began to rise during the Jurassic, which was probably caused by an increase in
seafloor spreading. The formation of new crust beneath the surface displaced ocean waters by as much as 200 m more than today, which flooded coastal areas. Furthermore, Pangaea began to rift into smaller divisions, bringing more land area in contact with the ocean by forming the
Tethys Sea. Temperatures continued to increase and began to stabilize.
Humidity also increased with the proximity of water, and deserts retreated.
The climate of the Cretaceous is less certain and more widely disputed. Higher levels of
carbon dioxide in the
atmosphere are thought to have caused the
world temperature gradient from north to south to become almost flat: temperatures were about the same across the planet. Average temperatures were also higher than today by about 10 °
C. In fact, by the middle Cretaceous, equatorial ocean waters (perhaps as warm as 20 °C in the deep ocean) may have been too warm for sea life, and land areas near the equator may have been deserts despite their proximity to water. The circulation of
oxygen to the deep ocean may also have been disrupted. For this reason, large volumes of organic matter accumulated because they were unable to
decompose and were eventually
deposited as "
black shale".
Not all of the data support these hypotheses, however. Even with the overall warmth, temperature fluctuations should have been sufficient for the presence of
polar ice caps and
glaciers, but there's no evidence of either. Quantitative models have also been unable to recreate the flatness of the Cretaceous temperature gradient.
Life
The extinction of nearly all animal species at the end of the
Permian period allowed for the
radiation of many new lifeforms. In particular, the extinction of the large
herbivorous and
carnivorous dinocephalia left those
ecological niches empty. Some were filled by the surviving
cynodonts and
dicynodonts, the latter of which subsequently became extinct.
Animal life during the Mesozoic was dominated, however, by large
archosaurian
reptiles that appeared a few million years after the Permian extinction:
dinosaurs,
pterosaurs, and aquatic reptiles such as
ichthyosaurs,
plesiosaurs, and
mosasaurs.
The climatic changes of the late Jurassic and Cretaceous provided for further adaptive radiation. The Jurassic was the height of archosaur diversity, and the first
birds and
placental mammals also appeared.
Angiosperms radiated sometime in the early Cretaceous, first in the
tropics, but the even temperature gradient allowed them to spread toward the poles throughout the period. By the end of the Cretaceous, angiosperms dominated tree floras in many areas, although some evidence suggests that
biomass was still dominated by
cycad and
ferns until after the KT extinction.
Some have argued that
insects diversified with angiosperms because insect
anatomy, especially the
mouth parts, seems particularly well-suited for flowering plants. However, all major insect mouth parts preceded angiosperms and insect diversification actually slowed when they arrived, so their anatomy originally must have been suited for some other purpose.
As the temperatures in the seas increased, the larger animals of the early Mesozoic gradually began to disappear while smaller animals of all kinds, including
lizards,
snakes, and perhaps the ancestor
mammals to
primates, evolved. The KT extinction exacerbated this trend. The large archosaurs became extinct, while birds and mammals thrived, as they do today.
Further Information
Get more info on 'Mesozoic'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://mesozoic.totallyexplained.com">Mesozoic Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
