What are geological ages?

We explain what they are and what the geological ages are. In addition, what are the eons, periods, times and the geological table.

1. What are geological ages?

The geological ages of the Earth are the different formal temporal units in which geological time is divided and organized , that is, the history of the formation of our planet . Its duration corresponds to each eratema, which is the time it takes to form the rocks of a specific layer of soil.

Geological ages are the intermediate units between geological eons (major category) and geological periods (minor category). All this according to the Geological Time Scale (GTS) managed by specialists in the field.

The geological ages are evidenced from the fossil record and the constitution of the sedimentary layers of the earth’s crust , and allow us to temporarily classify and date the findings we make through excavations, such as fossils, rocks or minerals.

The duration of each era can be very variable, from a few hundred million years to almost a thousand, depending on the case. There are ten differentiated ages , since the end of the Hadic eon, the initial and undifferentiated stage of the precambrian supereon, about 4.6 billion years ago.

The division of the Geological Time Scale into eras began in the 19th century, when the pioneers of geology and paleontology began their excavation and research work, and faced the need to classify the Earth’s layers .

They noticed that the difference between one layer and another responded to certain climatic, geological and even biological conditions, so by digging deep, it was receding into geological time. The first three ages identified belong to the Phanerozoic eon, and are the ages that comprise life on the planet: Paleozoic, Mesozoic and Cenozoic.

2. The geological table

As with the rest of the Geological Time Scale classifications, the definition of the ages responds to conventions of scientists and specialists in the field, since the history of the planet is really a continuity.

However, thanks to this series of conventions, it was possible to establish the Geological Table or Geological Temporal Scale, which is an ordered and hierarchical diagram in which all the divisions of the planet’s history are detailed:

• Eons , the largest division of time lapses , occasionally organized into larger supereons still. Two eons are recognized: Phanerozoic (which begins 541 million years ago and leads to today) and Precambrian (which begins with the formation of the Earth and culminates with the explosion of life in the seas), although the latter can also be understood as a supereón, which contains three distinct eons: Hádico (4,600 to 4,000 million years ago), Arcaico (4,000 to 2,800 million years ago) and Proterozoic (2,500 to 635 million years ago).
• You were , of which we have been speaking, that constitute the large-scale divisions of each eon, comprising some hundreds of millions of years each.
• Periods (or systems) , which are the most specific divisions of each era, in which there were important changes in the biota (life) of the moment.
• Times , subdivisions of the periods, that attend to the general characteristics of the fauna and the flora in said period of time.

3. What are the geological ages?

As we said before, there are ten geological ages, comprised of four different eons:

Edic Hádico . There is no division into ages, since it is a time too remote and too primitive conditions in the formation of the planet, to leave salvageable and studyable evidence.

Archean . It comprises four different geological ages:

• It was Eoarcaic . It begins 4,000 million years ago and culminates approximately 3,600 million years ago. Its name comes from the Greek words Eo (“dawn”) and Archios (“ancient”), and it is where the oldest known rock formations formed. It is possible that life appeared in its first cellular forms in this era, but there are no fossil records to prove it.
• Paleoarchic era . It begins 3,600 million years ago and culminates 3,200 million years ago, and it is the era from which the oldest known fossil forms, such as bacteria and other primitive photosynthetic organisms (anoxigenic, that is, did not yet produce oxygen) come from.
• Mesoarchic era . It begins 3,200 million years ago and culminates 2,800 million years ago. This era witnessed the formation and fragmentation of the first supercontinent, called Vaalbará, and the first glaciation in history.
• It was Neoarcaic . It starts 2.8 billion years ago and culminates 2.5 billion years ago. It is the era in which microorganisms initiated oxygenic photosynthesis, that is, oxygen producing, forever changing the composition of the planetary atmosphere .

Proterozoic Aeon . It comprises three different ages:

• It was Paleoproterozoic . It begins 2.5 billion years ago and culminates 1.6 billion years ago. This era begins with a gigantic environmental change known as the Great Oxidation, a consequence of the photosynthesis sustained by the cyanobacteria of the sea. The main mountain belts that still survive today also emerged.
• Mesoproterozoic era . It begins 1.6 billion years ago and culminates about 1,000 million years ago. In it there is the rupture of the supercontinent of Columbia and the formation of another called Rodinia, as well as the substantial beginning of the fossil record, with red algae and cyanobacterial colonies.
• It was Neoproterozoic . It begins about 1,000 million years ago and culminates approximately 542 million years ago. It takes place the most extensive glaciation known in the geological record, in which the so-called “Snowball Earth” was formed. Towards its end the first multicellular organisms appear , among them the first aquatic animals.

Phanerozoic Aeon . It comprises three different ages, which are:

• Paleozoic era . Also called the Primary Era, it begins about 541 million years ago and culminates about 252 million years ago. Its name comes from the Greek and means “ancient life”, because in this era the most primitive higher life forms known from the fossil record emerged. It begins after the disintegration of the supercontinent Pannotia and culminates with the formation of another called Pangea , dominated by the first reptiles and byrelatively modern plants , such as conifers.
• It was Mesozoic . Also known as Secondary Era, it begins about 251 million years ago and culminates just 68 million years ago. Its name, as in the previous case, means “intermediate life”, since it is where most of the ancestors of modern life forms appear. In this the reign of the dinosaurs takes place, from its beginnings to its dramatic extinction, and also great orogenic events, such as the gradual fragmentation of Pangea and the positioning of the continents more or less in their current location.
• It was Cenozoic . Also called Tertiary Era, it started about 66 million years ago and extends to this day. Its name, similar to the two previous cases, means “new life”, since the world in this period of time reached its current configuration and modern life forms emerged, that is, the reign of mammals . The first superior primates appear in their last 30 million years, and among them the human being , barely 200,000 years ago.