Was Earth ever so cold that it was completely encased in ice?
There is a hypothesis that much of the planet was covered by ice at the end of the Precambrian. This hypothesis is called Snowball Earth. One line of evidence is the rapid evolution of life in the Ediacara and Cambrian periods. It is thought that when the ice melted and conditions were favorable, life evolved rapidly.
Precambrian Plate Tectonics
By the end of the Archean, about 2.5 billion years ago, plate tectonics processes were completely recognizable. Small Proterozoic continents known as microcontinents collided to create supercontinents, which resulted in the uplift of massive mountain ranges.
The history of the North American craton is an example of what generally happened to the cratons during the Precambrian. As the craton drifted, it collided with microcontinents and oceanic island arcs, which were added to the continents. Convergence was especially active between 1.5 and 1.0 billion years ago. These lands came together to create the continent of Laurentia.
About 1.1 billion years ago, Laurentia became part of the supercontinent Rodinia (Figure below). Rodinia probably contained all of the landmass at the time, which was about 75% of the continental landmass present today.
Rodinia as it came together about 1.1 billion years ago.
Rodinia broke up about 750 million years ago. The geological evidence for this breakup includes large lava flows that are found where continental rifting took place. Seafloor spreading eventually started and created the oceans between the continents.
The breakup of Rodinia may have triggered Snowball Earth around 700 million years ago.
This video explores the origin of continents and early plate tectonics on the young Earth (1c): http://www.youtube.com/watch?v=QDqskltCixA (5:17).
- About 2 billion years after Earth formed, plate tectonics processes were similar to those around today.
- Microcontinents collided together to create larger continents and supercontinents.
- The supercontinent of Rodinia came together about 1.1 billion years ago and broke apart about 750 million years ago.
Use this resource to answer the questions that follow.
1. What was the first continent?
2. When was Arctica formed?
3. When was Atlantica formed?
4. What happened 1.8 billion years ago?
5. How was Rodinia formed?
6. What is the driving mechanisms for the movement of the plates?
7. What produces the heat?
1. Why did it take 2 billion years for plate tectonics to be similar to the way it is today?
2. What evidence is there for Snowball Earth? What evidence would you look for to test the hypothesis?
3. After Rodinia broke apart, what happened to the continents?