Understanding Geological Time

What are the Geological Rock Stratum & Geological Time?

Graphical representation of Earth's history as a spiral.

https://commons.wikimedia.org/wiki/File:Geological_time_spiral.png

In order to understand the basics of all scientific fields, evolution & the earth as we know it, it is important to understand and comprehend geological time & earth's history.

Geological Time:

The extensive interval of time occupied by the geologic history of Earth. Formal geologic time begins at the start of the Archean Eon (4.0 billion to 2.5 billion years ago) and continues to the present day. Modern geologic time scales additionally often include the Hadean Eon, which is an informal interval that extends from about 4.6 billion years ago (corresponding to Earth’s initial formation) to 4.0 billion years ago. Geologic time is, in effect, that segment of Earth history that is represented by and recorded in the planet’s rock strata.

Geologic time scale evolution of life on Earth./imgur.com

Geological Rock Stratum:

Stratum, plural Strata, sedimentary rock layer bounded by two stratification planes, the latter being produced by visible changes in the grain size, texture, or other diagnostic features of the rocks above and below the plane. A stratum that is less than one centimeter (0.4 inch) in thickness is termed a lamina, whereas one greater than this thickness is a bed.

The first serious attempts to formulate a geologic time scale that could be applied anywhere on Earth were made in the late 18th century. The most influential of those early attempts (championed by Werner, among others) divided the rocks of Earth's crust into four types: Primary, Secondary, Tertiary, and Quaternary. Each type of rock, according to the theory, formed during a specific period in Earth history. It was thus possible to speak of a "Tertiary Period" as well as of "Tertiary Rocks." Indeed, "Tertiary" (now Paleogene and Neogene) remained in use as the name of a geological period well into the 20th century and "Quaternary" remains in formal use as the name of the current period. 

The identification of strata by the fossils they contained, pioneered by William Smith, Georges Cuvier, Jean d'Omalius d'Halloy, and Alexandre Brongniart in the early 19th century, enabled geologists to divide Earth history more precisely. It also enabled them to correlate strata across national (or even continental) boundaries. If two strata (however distant in space or different in composition) contained the same fossils, chances were good that they had been laid down at the same time. Detailed studies between 1820 and 1850 of the strata and fossils of Europe produced the sequence of geologic periods still used today.

https://www.britannica.com/science/geologic-time

Let's have a closer look at the details of life on earth in the different time periods.

Here is a diagram illustrating the basic details of the life on earth in different periods & eras,

followed by some amazing art that brings prehistoric life to life! 

This awesome art was created by by Masato Hattori.

I have been a massive fan of his painting, digital art & art style ever since I discovered his work.
Check out the awesome work Masato Hattori creates at: www.sciencephoto.com/contributor/mha

Ediacaran Period (635.0 to 538.8 Million Years Ago):

Cambrian Period (538.8 to 485.4 Million Years Ago):

https://www.sciencephoto.com/media/930654/view

Ordovician Period (485.4 to 443.4 Million Years Ago):

Silurian Period (443.4 to 419.2 Million Years Ago):

Devonian Period (419.2 to 358.9 Million Years Ago):

Carboniferous Period (358.9 to 298.9 Million Years Ago):

Permian Period (298.9 to 251.902 Million Years Ago):

Triassic Period (251.902 to 201.3 Million Years Ago):

Jurassic Period (201.3 to 145.0 Million Years Ago):

Cretaceous Period (145.0 to 66.0 Million Years Ago):

Early Pliocene to Late Holocene Period (5–0.0037 Million Years Ago):

I want to conclude with this amazing thought from: 

Shadows of Forgotten Ancestors by Carl Sagan & Ann Druyan:

"Had life and humans first come to be hundreds or even thousands of years ago, we might know most of what’s important about our past. There might be very little of significance about our history that’s hidden from us. Our reach might extend easily to the beginning. But instead, our species is hundreds of thousands of years old, the genus Homo millions of years old, primates tens of millions of years old, mammals over 200 million years old, and life about 4 billion years old. Our written records carry us only a millionth of the way back to the origin of life."

References, bibliography & further reading:

https://www.britannica.com/science/cartography

https://www.britannica.com/science/stratum-geology

https://en.wikipedia.org/wiki/Geologic_time_scale

A dictionary of geology and earth sciences. Michael Allaby (4th ed.). Oxford: Oxford University Press. 2013.