With the passing of the Archean, the earth had not yet settled into the perfectly balanced sphere which Nature destined it to be.
At the bottom of the sea were the Archean or igneous rocks, the oldest formation known to geology.
Yet either is inconsiderable against the total lapse of time even from the Archean's close till now.
It is to this lowermost gneissic group that the term “Archean” may be conveniently limited.
This vast period of time, which includes the beginning, is known among geologists as Archean time.
Australia is essentially the fragment of a great plateau land of Archean rocks.
The period following on after Archean time is called, by geologists, Paleozoic time.
The breaking up of the old Archean foundation block began in Cambrian and Ordovician times.
The definite history of the earth begins with the close of the dim Archean era.
At one time these rocks were regarded as Archean gneisses of a special type.
| Archean The earlier of the two divisions of the Precambrian Eon, from about 3.8 to 2.5 billion years ago. During this time the Earth had a reducing atmosphere consisting primarily of methane, ammonia, and other gases that would be toxic to most modern life forms. There was little free oxygen. Rocks from the earliest part of the Archean are predominantly volcanic and are similar to pillow basalts, suggesting that they formed underwater. Rocks from the later part of the Archean appear to have formed on continents. It is believed that about 70% of the continental masses formed during this time. Fossils preserved in rocks from this period of time include remains of cyanobacteria, the first single-celled forms of life. These organisms are preserved in the form of stromatolites and oncolites. See Chart at geologic time. |
