Dinosaurs roamed the planet for about 165 million years, during a time in the Earth’s history called the Mesozoic Era. It is difficult to imagine how long this was, until we compare it with ourselves: humans have lived on Earth for less than two million years. During the Mesozoic Era, the Earth’s landmasses changed dramatically, new seas were formed, and plants and animals evolved.
Geologists divide Earth’s long history into a series of time zones, from the origin of the planet, about 4,600 million years ago, right up to the present day. The major divisions are called eras. These are sub-divided into smaller time zones called periods. Within each period are smaller divisions called Ages (not shown in this diagram). Dinosaurs lived in the Mesozoic Era, which is divided into the Triassic, Jurassic and Cretaceous Periods. Humans live in the Quaternary Period of the Cenozoic Era.
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Chronological Timescale
Precambrian
4,600 - 545 MYA
The Precambrian or Pre-Cambrian, sometimes abbreviated pЄ, or Cryptozoic
Precambrian time covers the vast bulk of the Earth's history, starting with the planet's creation about 4.5 billion years ago and ending with the emergence of complex, multicelled life-forms almost four billion years later.
What Was Happening on Earth at This Time? You might ask..
The Precambrian is the earliest of the geologic ages, which are marked by different layers of sedimentary rock. Laid down over millions of years, these rock layers contain a permanent record of the Earth's past, including the fossilized remains of plants and animals buried when the sediments were formed... see more
The Earth was already more than 600 million years old when life began. The planet had cooled down from its original molten state, developing a solid crust and oceans created from water vapor in the atmosphere. Many scientists think these primordial seas gave rise to life, with hot, mineral-rich volcanic vents acting as catalysts for chemical reactions across the surface of tiny water bubbles, which led to the first cell membranes. Other bubbles are thought to have formed self-replicating substances by attracting chemicals from around them. Over time the two combined to produce energy-using, living cells.
The earliest living organisms were microscopic bacteria, which show up in the fossil record as early as 3.4 billion years ago. As their numbers multiplied and supplies of their chemical fuel were eaten up, bacteria sought out an alternative energy source. New varieties began to harness the power of the sun through a biochemical process known as photosynthesis—a move that would ultimately lead to simple plants and which opened the planet up to animal life.
Some three billion years ago, the Earth's atmosphere was virtually devoid of oxygen. At about 2.4 billion years ago, oxygen was released from the seas as a byproduct of photosynthesis by cyanobacteria. Levels of the gas gradually climbed, reaching about one percent around two billion years ago. About 800 million years ago, oxygen levels reached about 21 percent and began to breathe life into more complex organisms. The oxygen-rich ozone layer was also established, shielding the Earth's surface from harmful solar radiation.
Unfamiliar Life-Forms
The first multicelled animals appeared in the fossil record almost 600 million years ago. Known as the Ediacarans, these bizarre creatures bore little resemblance to modern life-forms. They grew on the seabed and lacked any obvious heads, mouths, or digestive organs. Fossils of the largest known among them, Dickinsonia, resemble a ribbed doormat. What happened to the mysterious Ediacarans isn't clear. They could be the ancestors of later animals, or they may have been completely erased by extinction.
A pink sponge, photographed at an aquarium today
Palaeozoic Era
545 - 250 MYA
Palaeozoic era also know as the Marine life
The Paleozoic began with the Cambrian Period, 53 million years best known for ushering in an explosion of life on Earth. This "Cambrian explosion" included the evolution of arthropods (ancestors of today's insects and crustaceans) and chordates (animals with rudimentary spinal cords). In the Paleozoic Era, life flourished in the seas. After the Cambrian Period came the 45-million-year Ordovician Period, which is marked in the fossil record by an abundance of marine invertebrates. Perhaps the most famous of these invertebrates was the trilobite, an armored arthropod that scuttled around the seafloor for about 270 million years before going extinct.
After the Ordovician Period came the Silurian Period (443 million years ago to 416 million years ago), which saw the spread of jawless fish throughout the seas. Mollusks and corals also thrived in the oceans, but the big news was what was happening on land: the first undisputed evidence of terrestrial life. This was the time when plants evolved, though they most likely did not yet have leaves or the vascular tissue that allows modern plants to siphon up water and nutrients. Those developments would appear in the Devonian Period, the next geological period of the Paleozoic. Ferns appeared, as did the first trees. At the same time, the first vertebrates were colonizing the land. These vertebrates were called tetrapods, and they were widely diverse: Their appearance ranged from lizardlike to snakelike, and their size ranged from 4 inches (10 cm) long to 16 feet (5 meters) long, according to a study released in 2009 in the Journal of Anatomy.
The skeleton of Eryops, one of the earliest land-walking tetrapods.
You must be wondering where are the monstrous lizards?
Carefull what you wish for...
The Mesozoic Era, Age Of Dinosaurs 250 - 65 MYA
During the Mesozoic, or "Middle Life" Era, life diversified rapidly and giant reptiles, dinosaurs and other monstrous beasts roamed the Earth. The period, which spans from about 250 million years ago to about 65 million years ago, was also known as the age of reptiles or the age of dinosaurs. The Mesozoic era is divided into 3 periods, the Triassic Period, Jurrasic Period and Cretaceous period. You may see the details of the said divions of the period below.
Triassic Period
250 - 200 MYA
Early in the Triassic, a group of reptiles, the order Ichthyosauria, returned to the ocean. Fossils of early ichthyosaurs are lizard-like and clearly show their tetrapod ancestry. Their vertebrae indicate they probably swam by moving their entire bodies side to side, like modern eels.
Arizonasaurus
Arizonasaurus was a ctenosauriscid archosaur from the Middle Triassic. learn more
A fairly complete skeleton was found in 2002 by Sterling Nesbitt. The taxon has a large sailback formed by elongated neural spines of the vertebrae. The type species, Arizonasaurus babbitti, was named by Samuel Paul Welles in 1947.
Placodus
Placodus is one of the most often represented reptiles of the placodont group, and the most common of the ‘unarmoured’ variety that seemed to be similar to marine iguanas. learn more
Unlike the algae eating marine iguana however, Placodus was a dedicated durophagous shellfish eater. In its search for food it used specialised forward pointing incisors to grip and pluck things like bivalves and crustaceans off the sea floor before taking them into the back of its mouth.
Plateosaurus
Plateosaurus is probably the best understood dinosaur currently known, and also one of the oldest dinosaur genera. learn more
Named in 1837, Plateosaurus actually predated the creation of the Dinosauria by Richard Owen in 1842, though the genus missed out on being one of the defining dinosaur genera (instead Owen used Megalosaurus, Iguanodon and Hylaeosaurus). Regardless of this, study of Plateosaurus has revealed that in terms of contribution to the science of palaeontology, Plateosaurus is one of the most important dinosaurs.
Jurrasic Period
200 - 145 MYA
Dinosaurs, birds, and rodents. Crumbling landmasses and inland seas. Sea monsters, sharks, and blood-red plankton. Forests of ferns, cycads, and conifers. Warm, moist, tropical breezes. This was the Jurassic.
Tyronnosaurus Rex
T. rex was a member of the Tyrannosauroidea family of huge predatory dinosaurs with small arms and two-fingered hands. learn more
T. rex was a huge carnivore and primarily ate herbivorous dinosaurs, including Edmontosaurus and Triceratops. The predator acquired its food through scavenging and hunting, grew incredibly fast and ate hundreds of pounds at a time, said University of Kansas paleontologist David Burnham.
Pterodactyl
Pterodactylus, also known as a pterodactyl, is an extinct pterosaur which lived approximately 150 million to 145 million years ago learn more
Pterodactylus is one of the most recognizable flying creatures to have ever lived on the Earth. Show just about anybody Pterodactylus pictures and they are able to at least tell you that it is a pterodactyl. The only other creatures that are that recognizable from this time period is Stegosaurus or maybe, Brachiosaurus.
Stegosaurus
Stegosaurus is a dinosaur that lived around 155 million years ago—during the Jurassic Period
An interesting fact to note is that of all of the dinosaurs, Stegosaurus had one of the smallest brains. Although the actual anatomy of this dinosaur’s brain is currently unknown, it is known that it only weighed approximately 3 ounces—which is extraordinarily small for a creature that weighed over 5 tons. As such, it is believed that this dinosaur was very simple and slow moving.
Cretaceous Period
145 - 65 MYA
The Cretaceous Period was the last and longest segment of the Mesozoic Era. It lasted approximately 79 million years, from the minor extinction event that closed the Jurassic Period about 145.5 million years ago to the Cretaceous-Paleogene (K-Pg) extinction event dated at 65.5 million years ago. In the early Cretaceous, the continents were in very different positions than they are today. Sections of the supercontinent Pangaea were drifting apart. The Tethys Ocean still separated the northern Laurasia continent from southern Gondwana. The North and South Atlantic were still closed, although the Central Atlantic had begun to open up in the late Jurassic Period. By the middle of the period, ocean levels were much higher; most of the landmass we are familiar with was underwater. By the end of the period, the continents were much closer to modern configuration. Africa and South America had assumed their distinctive shapes; but India had not yet collided with Asia and Australia was still part of Antarctica.
And then It happened, out of million chances, it hit earth
66 million years ago
Out of all the places in the world an asteroid could have walloped ancient Earth, the Yucatán Peninsula was possibly the worst. That’s the premise of a new study examining what happened 66 million years ago, after a 7.5-mile-wide asteroid crashed into the ocean near what’s now the port town of Chicxulub, Mexico. The impact brought the age of dinosaurs to an abrupt end, wiping out the vast majority of the iconic beasts along with about three-quarters of all life on Earth.
