Summary

During the Triassic period, 234 million years ago, a sudden change in climate caused by long-term volcanic eruptions triggered an episode of excessive rain and flooding for two million years (called the Carnian Pluvial Episode). With the rain came an explosion of plants. This allowed dinosaurs to take hold on our planet due to a greater abundance in food sources (i.e. plants that were able to thrive with the wetter climate). The rain changed the history of Earth by assisting in the survival and evolution of the dinosaurs.

Why Watch This Video?

Have you ever wondered how dinosaurs got their foothold on this planet?

Would you like to know how geologists can conclude what Earth’s climate was like in the past, and how the climate changed periodically from wet to dry periods?

Have you ever been confused by changes on Earth that can cause rain to occur for long periods of time?

Key Terms

Proliferation of giant plants

Proliferation is simply the rapid increase of numbers. Therefore, the proliferation of giant plants was the rapid increase of plants during the Triassic period. This included plants which grew to be very tall. For some dinosaurs, this was useful because as they grew taller, their food source was more abundant and easily accessible in comparison to other, shorter reptiles. Some scientists suggest conifers were able to become widespread during this time.

Pluvial

Pluvial means excess or increased rainfall. Therefore, the period during which it rained for two million years is marked as the Carnian Pluvial Episode. Carnian is the period of time from 237-228 million years ago during the Triassic. It is important to note that the Carnian Pluvial Episode was one of great humidity, ocean acidification and anoxia, and acid rain.

Wrangellian Eruptions

These volcanic eruptions are those that are thought to be responsible for the emergence of the Carnian Pluvial Episode. Occurring approximately 235 million years ago near Alaska and British Columbia, the massive amounts of carbon dioxide released by these eruptions triggered a change in water cycles, creating great humidity and intense rain. When the eruptions eventually stopped, earth was able to recover by soaking up its excess carbon dioxide and returning to a dryer climate.

 Loose Ends

It did not actually rain non-stop for two million years without any cessation.

While it indeed did rain phenomenal amounts during this episode, what is meant by non-stop rain is simply rain periods so extensive that it was unprecedented. The Earth was very dry before this event occurred, but once it began, rain-forest like rainfall took place in parts of the world completely uncharacterized to have that amount of rain. Monsoons were commonplace as was flooding, but this does not mean that the rain never stopped during this period; the rain was exceptional and widespread for the time.

What was the state of the oceans at the start of the Carnian Pluvial Episode?

As described in the video, before the rain fell, and climate began to sustain a more diverse array of life, the oceans were extremely warm. Few species of marine life had survived the Permian Extinction (about 95% died off), thus the diversification of species at this time was limited. It is in the Triassic however, that we begin to see the growth of corals. This loose end is relevant to the video because it begs the question, how much excess carbon dioxide can our oceans handle? The climate was able to return to its previous dryness due, in part, to the oceans soaking up the excess carbon dioxide.

Why was Earth able to soak up excess carbon dioxide and effectively stop global warming?

Earth carries a capacity to regulate itself and take in extra carbon dioxide, to a certain point. In combination with the oceans, plants and rocks have the capacity to soak up excess carbon dioxide. Unfortunately, there is a point that no more carbon dioxide and other greenhouse gasses can be soaked up and thus, it remains in the atmosphere. For the Earth to regain its dry climate, it was crucial that the Wrangellian Eruptions stopped, without this ceasing of eruptions, there is no telling how long the Carnian Pluvial Episode would have gone on for.

Self-Test Questions

Scroll down to see the answers.

1. What is the most likely explanation for why shorter reptiles died off in a wet climate?

1. They drowned in floods
2. They were unable to reach tall plant food sources
3. They were eaten by mammals
4. Their eggs could not hatch in a wet climate

2. Which species was so widespread in the Triassic that its fossils helped lead to the idea of plate tectonics?

1. Lystrosaurus
2. Tyrannosaurus
3. Edmontosaurus
4. Ichthyosaurus

3. How much of the fossil record of “terrestrial vertebrates” did dinosaurs account for at the beginning and then at the end of the Carnian Pluvial Episode? (beginning first, then end)

1. 10% and 70%
2. 1% and 5%
3. 90% and 5%
4. 5% and 90%

4. What caused the rain to end?

1. Volcanic eruptions
2. Change in lunar patterns
3. Excess carbon soaked up by plants, rocks and oceans
4. It stopped for no reason

5. How did the climate change to cause so much rain?

1. Excess wind caused clouds to move more
2. Volcanic eruptions created excess carbon dioxide in the atmosphere
3. End of an ice-age
4. There was a tear in the ozone layer

Answers

1. B, In a wet climate, it would have been crucial for a creature’s survival to be able to stand on its hind legs and reach taller food sources. In a climate that is dry, plants tend to grow near to the ground. In a wet climate, plants and trees have the ability to grow sky-high, making it impossible for those with short legs to obtain their food source. With less competition for food, and the ability to grow tall and reach plants, the dinosaurs were able to continue to grow and evolve.

2. A, The fact that Lystrosaurus was found on so many continents allowed scientists to deduce that there must be some mechanism in which all continents were joined and then torn apart in Earth’s history.

3. D, At the start of the Pluvial Episode, life was recovering from the End-Permian Extinction and the dinosaurs had not yet taken hold on our planet. By the end of the Carnian Pluvial, dinosaurs were able to diversify due to extinction of competitors and more widespread food sources.

4. C, When our planet has too much carbon in our atmosphere for extended periods of time, plants are able to absorb the carbon into their tissues. Rocks also absorb carbon, along with the ocean which turns the carbon into limestone.

5. B, Before and during the Carnian Pluvial Episode, volcanoes in Alaska and British Columbia began to erupt which released enough Carbon Dioxide in the air to raise temperatures between 3 and 10 degrees Celsius for the whole world. Warmer climates create a faster water cycle in which evaporation occurs and eventually falls to the ground as rain.