Geologic-Time-scale

Geologic Time Scale

What is the Geologic Time scale?

The geological time scale is based on the geological rock record, which includes disintegration, mountain structure and various other geological occasions. Over hundreds to countless millions of years, continents, oceans and also mountain ranges have relocated vast distances both vertically as well as horizontally.

Like the periodic table, the Geologic time scale is one of those remarkable human efforts to turn a huge amount of proof from astronomy, rocks, fossils, history and natural politics right into a great diagram which makes the entire thing show up nice, cool as well as resolved.

After Charles Darwin’s paper origin of Species (Darwin himself was likewise a geologist) in 1859, geologists understood that certain fossils were limited to particular layers of rock. This developed the very first generalized geological time range.

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The whole of the geologic history has been divided into units of varying magnitudes which together comprise the time scale of Earth’s history. These units show periods in earth history when major rock strata were formed.

Principle of Superposition

According to this, the layers of sedimentary rocks should occur in a sequence of their deposition, with the newer strata on the top of the older, but subsequent events may have changed the relationship of layers.

Not all strata occur in any one region, for some lands were exposed when others were submerged. In some regions, strata formed previously have subsequently emerged and eroded away so that relatively recent ones were then deposited on very ancient ones.

Certain sections of Earth have undergone tremendous folding and splitting so that older strata may now be resting on top of newer and younger ones.

Construction of Earth History

Geologists have developed methods for dating and arranging geologic events in meaningful, chronological order based on the ages of rock units. These time units give an idea as to when the animals and plants lived but in terms of relative time rather than the absolute one.

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Eras

The largest units of geologic time are called Eras. These immense units are marked by physical breaks in geological records called “Revolutions”. These revolutions raised or lowered vast regions of Earth’s surface and created or eliminated shallow inland seas.

These revolutions made changes in the distribution of seas and land organisms and erased many of the previous and ancient life forms.

For example, the era Palaeozoic ended with the revolution that raised the Appalachian Mountains and is thought to kill 3% of existing forms of life.

Five Geologic Eras

The five geologic eras are

  • Archaeozoic
  • Proterozoic
  • Palaeozoic
  • Mesozoic
  • Cenozoic
Periods

Each era is further divided into time units called Periods. Each period is characterized by a somewhat less profound change in life forms as compared to eras.

The Palaeozoic has 7, Mesozoic has 3 periods. We are living in Cenozoic era so there is a probability of more periods to come.

Epochs

Each of the periods is subdivided into smaller units called Epochs. Only periods of the Cenozoic era have names for seven epochs otherwise the epochs are not commonly referred to by specific names.

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Rather the terms “early”, “middle” and late are commonly used. For example, the epochs for the Devonian period have no specific names. They are called “Early Devonian”, “Middle Devonian” and Late Devonian.