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Mesozoic
("Middle Life") Era
This is the second of three geologic eras squeezed into the Phanerozoic
("Evident Life") Eon that covers the last 10% of Earth's
whole geologic history. This is the era we all think of when we
imagine the Ancient Earth! Rampaging dinosaurs! Dive-bombing pterodactyls!
Endless forests of giant ferns! Erupting Volcanoes! (Sorry, no cave
men! They didn't show up until the end of the Cenozoic.)
The Mesozoic Era lasted
about 180 million years, from about 245 million years ago to about
65 million years ago. The Mesozoic is divided into just three time
periods: the Triassic, the Jurassic, and the Cretaceous. Since lots
of things were going on in each time period, we can only summarize
the events. You can learn more by going to your library or searching
the Internet for words like "Mesozoic" or the names of
each of the periods.
In the view above, we
see Earth in the middle of the Jurassic Period, in mid-Mesozoic
times (sort of a middle-middle view). The supercontinents Gondwanaland
and Laurasia collided some time back to form a single super-super
continent called Pangea ("All-Earth"). But plate tectonics
continues its irresistible motions, and even as we look, Pangea
is beginning to break up into the continents we know now. At upper
left, North America is just breaking away from the northwest coast
of Africa, and the Atlantic Ocean and Gulf of Mexico are beginning
to form. The Appalachian Mountains of the eastern United States
are a high, rugged mountain range, something like the Rocky Mountains
of today. Over the next fifty million years or so, South America,
India, and Antarctica will all break away from Africa and move toward
their present positions.
Life is diversifying
rapidly, and beginning to look familiar. The dominant animals on
both land and sea are reptiles, the most famous of which are the
dinosaurs. Dinosaurs began in the Triassic, spread during the Jurassic,
and dominated Earth in the Cretaceous. They are so prominent that
the Mesozoic is also called "The Age of Reptiles." But
dinosaurs are not the only life form around: birds and mammals also
appear during the Mesozoic, as well as deciduous trees and flowering
plants.
The
climate during the Mesozoic is warm; so
warm that there are no ice caps at all,
even at the poles! Plants grow like crazy
in the warmth and moisture, so there is
food everywhere for your average hungry
50-ton Ultrasaurus! So what happened to
this Dino Paradise? More change! A mass
extinction like those in the Paleozoic
ended the idyllic Mesozoic Era (if you
can call dodging your friendly local T-Rex
as idyllic). More than half of all existing
life forms disappeared, including virtually
all of the dinosaurs. Why? There are many
hypotheses, including disease, volcanic
eruptions, and giant impacts. (Pay a visit
to the Dinosaur
Floor to learn more.
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