miércoles, 23 de mayo de 2012

GEOLOGICAL TIME SCALE - Eras & periods of our Earth's History

The geologic time scale is a method used to chronologically measure the different eras and periods of Earth's history, it relates stratigraphy to time. It is used by geologists, paleontologists, and other earth scientists to describe the timing and  relationships between events that have occurred throughout our Earth's history.
Geologic time scale showing ages

The Precambrian Era:

The name means: "before the Cambrian period." This term was originally used to refer to the whole period of earth's history before the oldest rocks with recognizable fossils in them were formed.This era covers almost 90% of the entire history of the Earth. It has been divided into three eras: the Hadean, the Archean and the Proterozoic.

This era began with the formation of the earth, during this era the surface of the Earth was full of oceans of liquid rock, boiling sulfur, and impact craters all over the place! Volcanoes blast off everywhere, and the rain of rocks and asteroids from space never ends. 
Begins about a billion years after the formation of the earth. Mostly everything has cooled down by this time. Most of the water vapor that was in the air has cooled and condensed to form a global ocean.
It began about two billion years after the earth was formed  and lasted about another two billion years! There is a lot more land to be seen, in fact, there are two supercontinents. Life is found only in the ocean, somewhere around 1.7 billion years ago, single-celled creatures appeared and these had a real nucleus.

The Paleozoic Era: 

This Era is the beginning of an explosion of life forms. The Cambrian Explosion marks the era with thousands of new living organisms in the ancient seas. There certainly was life before the Cambrian Period. Geologically, the Paleozoic starts not long after a supercontinent called Pannotia breaks up and at the end of the global glaciation and Snowball Earth. Ending this era the continents started to gather into a supercontinent called Pangaea. This is the longest of the eras, and it is subdivided into six geologic periods wich are the following: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. ( from oldest to yougest).

Living organisms in the ancient seas!

The Cambrian period:

It is the time when most of the major groups of animals first appear in the fossil record. 
This event sometimes is called the "Cambrian Explosion," because of the relatively short time
over which this diversity of forms appears. In this time there was no life on land and 
little or none in freshwater the sea was centre of living activity.

Animation of life in the Cambrian

The Ordovician period:

The Ordovician Period is the second period of the Paleozoic Era. This period saw the origin and rapid evolution of many new types of invertebrate animals which replaced their Cambrian predecessors. Life forms diversified dramatically and  many of the marine forms familiar today appeared. Primitive vascular plants appeared the land, also the supercontinent of Gondwana drifted to the south pole, later in this period one of the greats Ice Ages took place. The end of the period is marked by a major extinction event.

Mysterious creatures of the Ordovician period!

The Silurian period:

The melting of the Ordovician glacial ice produced a warm, stable climate providing the perfect conditions for Life to flourish. Silurian plants developed a vascular structure giving their stalks the strength to grow as high as three feet without the support of a watery environment.The animal kingdom was expanding hiding among the new plants we find the first evidence of animal life on land consisting of fossilized insects such as millipedes and spiders. 

Mysterious creature of the Silurian period!

The Devonian period:

During this period the first fish developed legs and moved onto land as tetrapods and there were many types of terrestrial arthropods. The first seed bearing plants spread and formed huge forests.The first ammonite mollusks appeared, great coral reefs were still common. The main land masses were called: Gondwana, Siberia, and Euramerica. This era was also called ”Age of Fishes”.

 Fish in the Devonian seas!
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The Carboniferous period:

In this period  the earth had the highest atmospheric oxygen levels, the evolution of the first reptiles was taking place. Plants grew and died at a fast pace forming coal. Although the Carboniferous started off warm the temperature began to drop and the polar regions went into an ice age that lasted millions of years. 

                                                                                Sharks and fish of the carboniferous period

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The Permian period:

In the Permian  the early amniotes divided into the ancestral groups of the mammals, turtles, lepidosaurs and archosaurs. The world was a large mass of land called Pangaea, surrounded by an ocean called Panthalassa. The rainforests of the carboniferous disappeared leaving regions of arid desert in land. Reptiles, who could cope with the dryer conditions, rose to dominance. The Permian Period ended with the largest extincion  in which nearly 90% of marine species and 70% of terrestrial species disappeared    

                                                   Permian sea life and some reptiles existent
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The Mesozoic Era:

In this era the climate was warmer, the seasons were milder, the sea levels were higher, and there was no polar ice. The continents were jammed together, forming the supercontinent Pangaea, but this supercontinent would start breaking up towards the middle of the Mesozoic Era. After the mass extinction wich took place at the end of the Paleozoic Era, there was an explosion of new life forms, which included the dinosaurs and mammals, and later in the Mesozoic, birds and flowering plants.  This era was divided into three different periods: Triassic, Jurassic and Cretaceous (from oldest to youngest).

                                                                      The three periods of the Mezosozoic Era                                                                                        

The Triassic period:

The Triassic was the first part of Mesozoic. This time is often referred to as the "age of dinosaurs," since dinosaurs were the most notable, successful and diverse creatures to emerge during the Triassic. In this period the world's first true mammals emerged. The climate was mild, warm or scorching hot, depending on the location.

                                                                         Land mass od the Triassic period

The Jurassic period:

During this period, vegetation was greener and more lush. Later in this period, huge dinosaurs walked the lands, the earliest known birds also appeared.The climate was hot and dry and at the beginning of the Jurassic, strongly seasonal. The supercontinent Pangaea, was beginning to drift apart. 
       & Stegosaurus  

The Cretaceous period:

The Cretaceous Period began with the Earth’s land assembled essentially into two continents, Laurasia in the north and Gondwana in the south. The climate was generally warmer and more humid. Dinosaurs were the dominant group of land animals, flowering plants (angiosperms)started to appear close to the beginning of the Cretaceous and became more abundant as the period progressed. Toward the end of this period one of the greatest mass extinctions took placeexterminating the dinosaurs, marine and flying reptiles, and many marine invertebrates.

   Animals of the Cretaceous

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The Cenozoic Era:

As the dinosaurs perished at the end of the Cretaceous, mammals took center stage. Even as mammals increased in numbers and diversity, so did the birds, reptiles, fish, insects, trees, grasses, and other forms of life. Flowering plants strongly influenced the evolution of both birds and herbivores throughout the Cenozoic era by providing a rich abundance of food. The Earth started to dry out and cool down. The continents also began looking roughly familiar at this time and moved into their current positions.

                                             Arrangement of land masses in the Cenozoic Era

The Tertiary period:

Tertiary is often referred to as the ‘Age of Mammals’. However, there were other types of organisms that experienced great succes during this periodFor example, birds and flowering plants and insects continued to diversify, coevolving with plants. Life on Earth became  more similar to that of today. Many major groups, such as the mammals, birds and flowering plants diversifyed and  evolved into their contemporary orders, families and even genera in this period. Also the earliest primates and human ancestors appeared during the tertiary.

                                                                   Some mammals and reptiles existent in the Tertiary

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The Quaternary period:

The Quaternary is the most recent geological period of time in Earth’s history, spanning the last two million years and extending up to the present day. The Quaternary period is subdivided into the Pleistocene  (“Ice Age”) and the Holocene (present warm interval) epochs. The Mammals and Megafauna (large mammals) that evolved during this time like the caribou, the musk ox and the polar bear, still are an important part of the arctic fauna, however some did go extinct (mammoths). Also during this time humans evolve and develop the use of technology, language, art and religion.

    The age of mammals

Interesting stuff!:

Prehistoric Time Line, Geologic Time Scale- NG

Virtual tour of Victoria - Melbourne Museum 600 million years evolve

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