Mesozoic

Mesozoic signposts are colored blue. The images show the art on the Trek Through Time signposts. The name of each period is a link to the entire plaque installed on the Trek Through Time.

The Triassic Period: 252 to 201 million years ago

What did Earth look like during the Triassic Period?

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• Although the super continent Pangaea existed throughout the Triassic, the forces that formed it immediately began to pull it apart.
• Pangaea began to rotate with different plates rotating in different directions at different rates.
• The resulting tension caused a series of rips in the continent, and the Earth sagged down into these rips forming rift basins.
• During the Triassic, these rift basins (or rift valleys) developed between North America and Europe and between Africa and South America.
• With continued separation throughout the Jurassic Period, these basins became the Atlantic Ocean and the Gulf of Mexico.
• Other rifts later split off Antarctica, India, and Australia.

What was Earth’s climate like during the Triassic Period?

• The climate during much of the Triassic was warm with a dry continental interior and no evidence of ice at the poles.

What animals were on Earth during the Triassic Period?

• After the great extinction at the end of the Permian, many new kinds of animals evolved during the Triassic.
• The dominant land animals were reptiles.
• The first dinosaurs, marine reptiles, lizards, and tortoises appeared. 
• Mammals appeared during the Triassic, but they remained insignificant until their competitors, the dinosaurs, became extinct at the end of the Cretaceous.
• Crocodiles were abundant. It was in this period that insects attained complete metamorphosis.

What plants were on Earth during the Triassic Period?

• There were climatic variations due to alternating wet/dry and cold/hot seasons that influenced the distribution of plant communities.
• Conifers, cycads, and ferns were common.

The Jurassic Period: 201 to 145 million years ago

What did Earth look like during the Jurassic Period?

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• The breakup of Pangaea that began in the Triassic continued, and the early Atlantic Ocean and the Gulf of Mexico appeared as shallow continental seas.
• Shallow inland seas covered parts of the western United States.

What was Earth’s climate like during the Jurassic Period?

• Warm tropical greenhouse conditions occurred worldwide.

What animals were on Earth during the Jurassic Period?

• Giant plant-eating dinosaurs roamed the Earth with smaller but vicious carnivores stalking them.
• Flying reptiles and the first birds appeared.
• Creeping about in the undergrowth were tiny mammals no bigger than rats.
• The shallow oceans contained abundant life from tiny plankton to huge, whale-sized marine reptiles.

What plants were on Earth during the Jurassic Period?

• Conifers continued to be the most diverse large trees.
• Cycads (evergreen, cone-bearing, palm-like plants) became so abundant and diverse that the Jurassic is sometimes called the "Age of Cycads."

What was Virginia like during the Jurassic Period?

• As the Atlantic Ocean opened, east-flowing rivers such as the James and the Roanoke developed.
• Along the rift valleys, volcanoes were active.

What was Virginia like during the Jurassic Period?

• These sediments are present as sandstones and shales in VA today.

The Cretaceous Period: 145 to 66 million years ago

What did Earth look like during the Cretaceous Period?

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• The Atlantic Ocean continued to lengthen and widen, particularly to the south, which split South America from Africa.
• India separated and became an island continent.
• Much of each continent was covered with shallow continental oceans and inland seas.
• North America, Europe, Asia, and Africa became a series of islands. 
• The part of the US between the Rocky Mountains and the Appalachians and Ozarks was mostly underwater.

What was Earth’s climate like?

• During the Late Cretaceous, with rising sea levels and separated continents, shallow ocean currents carried warm water farther toward the poles.
• This created a mild global climate with ice-free poles.

What animals were on Earth during the Cretaceous Period?

• At least initially, dinosaurs and marine reptiles continued to flourish, and many new species appeared.
• Birds diversified and expanded in numbers, and they may have been the reason that flying reptiles decreased significantly.
• There were many new mammals, including the three groups that live today.
• Due to the appearance of flowering plants, many modern groups of insects appeared and began to diversify, including ants, termites, bees, butterflies, aphids, and grasshoppers.

What plants were on Earth during the Cretaceous Period?

• One of the most significant developments during the Cretaceous was the appearance and rapid diversification of the first flowering plants.

What was Virginia like during the Cretaceous Period?

• A shallow sea, part of the early Atlantic Ocean, covered eastern Virginia.

What else happened during the Cretaceous Period?

• A large meteorite crashed into the Gulf of Mexico 66 million years ago, causing a massive tsunami and a climate disruption that killed up to 80% of the world's animal and plant species, the last of the dinosaurs being the most noticeable victims.
• This mass extinction event separates the Mesozoic from the Cenozoic Era.

Onward to the Cenozoic!

Backward to the Paleozoic

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