Planet Earth - The Rhyacian Period

The Rhyacian Period ran from 2,300 to 2,050 million years ago.

Groups of intrusions started to form, but what are intrusions? Wikipedia, our friend through this journey through time, describes "an intrusion as liquid rock that forms under the Earth's surface." But it is so much more than this - this liquid rock or magma pushes up through cracks and spaces through the planet's surface to form a different form of solid rock and this process can take millions of years to develop. The magma cools or crystalises into minerals. But when you are talking of a period of the Earth's history that is 250 million years old, the development of intrusions are easy. Don't forget that the last post talked of the increase of mineral diversity or catastrophe three. To remind yourself of what an intrusion may look like - remember Devil's Tower National Monument from the film Close Encounters of the Third Kind - that is one. The intrusions that were developed during the Rhyacian period included the Sierra Nevada Mountains and the Bushveld Complex.

Another event defined the activity within the Rhyacian Period - this was the development of the eukaryotes. Remember how you were introduced to LUCA a few posts ago. So LUCA split into the three forms that we still know today; the single-celled, the archaea and the eukaryote. 

So what is a eukaryote? It is an organism that contains complex structures with cells that have membranes, which also contains its own copy of genetic material contained within the nucleus. They also contain specific and specialised equipment within a cell, these may be mitochondria (remember these?) or chloroplasts (these help plants make energy from solar energy. So the Rhyacian Period was when the eukaryote started to develop, I won't spoil the ending but have a look around you and see what could be a eukaryote.

Planet Earth was still covered in snow and ice due to the conversion of the primitive atmosphere from methane to carbon dioxide and a abundance of water vapour. This first ice age was known as the Huronian Ice Age or the Makganyene glaciation. It is thought to have ended around between 2,200 and  2,100 million years ago.

Evidence of this glacial period has been found in Lake Huron where there were there have found sediments from three glacial periods interspersed with non glacial periods. The latter name, Makganyene, refers to similar deposits laid down in the Transvaal group of mountains in South Africa. Why do we worry about these names and the evidence that they provide? I guess, it is to see where we are going and what we have missed, in the words of G. K. Chesterton:

"The disadvantage of men not knowing the past is that they do not know the present" (1933)

Next time - Another period but which one?