Eras of the Phanerozoic:
The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 541 million years to the present, and began with the Cambrian Period when diverse hard-shelled animals first appeared. The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic, which are further subdivided into 12 periods.
■ The Paleozoic features the rise of fish, amphibians and reptiles.
■ The Mesozoic is ruled by the reptiles, and features the evolution of mammals, birds and more famously, dinosaurs.
■ The Cenozoic is the time of the mammals, and more recently, humans.
The Paleozoic is a time in Earth’s history when complex life forms evolved, took their first breath of oxygen on dry land, and when the forerunners of all life on Earth began to diversify. There are six periods in the Paleozoic era: Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian.
The Cambrian is the first period of the Paleozoic Era and starts from 541 to 485 million years ago. The Cambrian sparked a rapid expansion in evolution in an event known as the Cambrian Explosion during which the greatest number of creatures evolved in a single period in the history of Earth. Almost all marine phyla evolved in this period. During this time, the super-continent Pannotia began to break up, most of which later recombined into the super-continent Gondwana.
The Ordovician spans from 485 million years to 440 million years ago. The Ordovician was a time in Earth’s history in which many species still prevalent today evolved, such as primitive fish, cephalopods, and coral. The most common forms of life, however, were trilobites, snails and shellfish. By the end of the Ordovican, Gondwana had moved from the equator to the South Pole, and Laurentia had collided with Baltica, closing the Iapetus Ocean. This is considered the first mass extinction and the second deadliest in the history of Earth.
The Silurian spans from 440 million years to 415 million years ago, which saw a warming from Snowball Earth. This period saw the mass evolution of fish, as jaw-less fish became more numerous, jawed fish evolved, and the first freshwater fish evolved, though arthropods, such as sea scorpions, remained the apex predators. Fully terrestrial life evolved, which included early arachnids, fungi, and centipedes. The evolution of vascular plants allowed plants to gain a foothold on land. During this time, there were four continents: Gondwana (Africa, South America, Australia, Antarctica, India), Laurentia (North America with parts of Europe), Baltica (the rest of Europe), and Siberia (Northern Asia).
The Devonian spans from 415 million years to 360 million years ago. Also known as the “Age of the Fish”, the Devonian features a huge diversification in fish, including armored fish like Dunkleosteus and lobe-finned fish which eventually evolved into the first tetrapods.
The Carboniferous spans from 360 million to 300 million years ago. During this period, average global temperatures were exceedingly high: the early Carboniferous averaged at about 20 degrees Celsius (but cooled to 10 degrees during the Middle Carboniferous). Tropical swamps dominated the Earth, and the large amounts of trees created much of the carbon that became coal deposits (hence the name Carboniferous). The high oxygen levels caused by these swamps allowed massive arthropods, normally limited in size by their respiratory systems, to proliferate.
The Permian spans from 300 million to 250 million years ago and was the last period of the Paleozoic Era. At its beginning, all continents came together to form the super-continent Pangaea, surrounded by one ocean called Panthalassa.
The Mesozoic ranges from 252 million to 66 million years ago. Also known as “the Age of the dinosaurs”, the Mesozoic features the rise of reptiles on their 150 million year conquest of the Earth on the land, in the seas, and in the air. There are three periods in the Mesozoic: Triassic, Jurassic, and Cretaceous.
The Triassic ranges from 250 million to 200 million years ago. The Triassic is a desolate transitional time in Earth’s history between the Permian Extinction and the lush Jurassic Period. It has three major epochs: Early Triassic, Middle Triassic and Late Triassic.
The Early Triassic lasted between 250 million to 247 million years ago, and was dominated by deserts as Pangaea had not yet broken up, thus the interior was arid.
The Middle Triassic spans from 247 million to 237 million years ago. The Middle Triassic featured the beginnings of the breakup of Pangaea, and the beginning of the Tethys Sea. The ecosystem had recovered from the devastation of the Great Dying.
The Late Triassic spans from 237 million to 200 million years ago. Following the bloom of the Middle Triassic, the Late Triassic featured frequent rises of temperature, as well as moderate precipitation (10-20 inches per year).
The Jurassic ranges from 200 million to 145 million years ago, and features three major epochs: Early Jurassic, Middle Jurassic, and Late Jurassic.
The Early Jurassic Epoch spans from 200 million to 175 million years ago. The climate was much more humid than the Triassic, and as a result, the world was very tropical. The first true crocodiles evolved, pushing the large amphibians to near extinction. The reptiles rose to rule the world.
The Middle Jurassic Epoch spans from 175 million to 163 million years ago. During this epoch, reptiles flourished as huge herds of sauropods, such as Brachiosaurus and Diplodicus, filled the fern prairies of the Middle Jurassic.
The Late Jurassic Epoch spans from 163 million to 145 million years ago. The Late Jurassic featured a massive extinction of sauropods and ichthyosaurs due to the separation of Pangaea into Laurasia and Gondwana in an extinction known as the Jurassic-Cretaceous extinction. The divided world would give opportunity for the diversification of new dinosaurs.
The Cretaceous is the longest period in the Mesozoic, spans from 145 million to 66 million years ago, and is divided into two epochs: Early Cretaceous, and Late Cretaceous.
Early Cretaceous Epoch
The Early Cretaceous Epoch spans from 145 million to 100 million years ago. The Early Cretaceous saw the expansion of seaways, and as a result, the decline and extinction of sauropods (except in South America). More importantly, the first true birds evolved sparking competition between them and the pterosaurs.
Late Cretaceous Epoch
The Late Cretaceous Epoch spans from 100 million to 65 million years ago. The Late Cretaceous featured a cooling trend that would continue into the Cenozoic Era. Eventually, tropical ecology was restricted to the equator and areas beyond the tropic lines featured extreme seasonal changes of weather. Every living thing with a body mass over 10 kilograms became extinct, and the age of the dinosaurs came to an end.
The Cenozoic featured the rise of mammals as the dominant class of animals, as the end of the age of the dinosaurs left significant evolutionary vacuums. There are three divisions of the Cenozoic: Paleogene, Neogene and Quaternary.
The Paleogene spans from the extinction of the dinosaurs, some 66 million years ago, to the dawn of the Neogene 23 million years ago. It features three epochs: Paleocene, Eocene and Oligocene.
The Paleocene Epoch began with the K-T extinction event caused by the impact of a metorite in the area of present-day Yucatan Peninsula and caused the destruction of 75% of all species on Earth. The Early Paleocene saw the recovery of the Earth from that event. The continents began to take their modern shape. The oceans were dominated by sharks as the large reptiles that had once ruled became extinct. Archaic mammals, such as creodonts and early primates that evolved during the Mesozoic filled the world. During this time there were no land creatures over 10 kilograms. Mammals were still quite small.
The Eocene Epoch ranged from 56 million to 34 million years ago. In the early Eocene, land animals were small and living in cramped jungles, much like the Paleocene. None had a mass over 10 kilograms. Among them were early primates, whales and horses along with many other early forms of mammals. At the top of the food chains were huge birds, such as Gastornis. In the Middle Eocene Epoch, the circum-Antarctic current between Australia and Antarctica formed which disrupted ocean currents worldwide, resulting in global cooling, and caused the jungles to shrink. The late Eocene Epoch saw the rebirth of seasons, which caused the expansion of savanna-like areas, along with the evolution of grass.
The Oligocene Epoch spans from 33 million to 23 million years ago. The Oligocene featured the expansion of grass which had led to many new species to take advantage, including the first elephants, cats, dogs, marsupials and many other species still prevalent today.
The Neogene spans from 23.03 million to 2.58 million years ago. It features 2 epochs: the Miocene, and the Pliocene.
The Miocene spans from 23.03 to 5.333 million years ago and is a period in which grass spread further across, effectively dominating a large portion of the world, diminishing forests in the process. Kelp forests evolved, leading to the evolution of new species, such as sea otters. The Tethys Sea finally closed with the creation of the Arabian Peninsula and in its wake left the Black, Red, Mediterranean and Caspian Seas. This only increased aridity. Many new plants evolved, and 95% of modern seed plants evolved in the mid-Miocene.
The Pliocene lasted from 5.333 to 2.58 million years ago. The Pliocene featured dramatic climactic changes, which ultimately led to modern species and plants. The Mediterranean Sea dried up for several million years. The Earth’s continents and seas moved into their present shapes. The world map has not changed much since, save for changes brought about by the glaciations of the Quaternary, such as the Great Lakes.
The Quaternary spans from 2.58 million years ago to present day, and is the shortest geological period in the Phanerozoic Eon. It features modern animals, and dramatic changes in the climate. It is divided into two epochs: the Pleistocene and the Holocene.
The Pleistocene lasted from 2.58 million to 11,700 years ago. This epoch was marked by ice ages as a result of the cooling trend that started in the Mid-Eocene. There were at least four separate glaciation periods marked by the advance of ice caps as far south as 40 degrees N latitude in mountainous areas.
The Holocene began 11,700 years ago and lasts until to present day. All recorded history and “the history of the world” lies within the boundaries of the Holocene epoch. Human activity is blamed for a mass extinction that began roughly 10,000 years ago, though the species becoming extinct have only been recorded since the Industrial Revolution. This is sometimes referred to as the “Sixth Extinction”. More than 322 species have become extinct due to human activity since the Industrial Revolution.
The Neolithic was a period in the development of human technology, beginning about 10,200 BC and ending between 4500 and 2000 BC. Traditionally considered the last part of the Stone Age or The New Stone Age, the Neolithic followed the terminal Holocene Epipaleolithic period and commenced with the beginning of farming, which produced the “Neolithic Revolution”. The beginning of the Neolithic culture is considered to be in the Levant (Jericho, modern-day West Bank) about 10,200–8800 BC. The Natufian period lasted between 12,500 and 9,500 BC, and the so-called “proto-Neolithic” is now included in the Pre-Pottery Neolithic (PPNA) between 10,200 and 8800 BC. The term Neolithic derives from the Greek word literally meaning “New Stone Age”. The term was invented by Sir John Lubbock in 1865 as a refinement of the three-age system. The Stone Age is the first period in the three-age system of archaeology, which divides human technological prehistory into three periods:
■ The Stone Age
■ The Bronze Age
■ The Iron Age
The Chalcolithic period or Copper Age, also known as the Eneolithic (from Latin aeneus “of copper”), was a period in the development of human technology, before it was discovered that adding tin to copper formed the harder bronze, leading to the Bronze Age. The Copper Age was originally defined as a transition between the Neolithic and the Bronze Age, but is now usually considered as belonging to the Neolithic. The archaeological site of Belovode on the Rudnik Mountain in Serbia contains the world’s oldest securely dated evidence of copper smelting from 5000 BCE.
The Bronze Age
The Bronze Age is a historical period characterized by the use of bronze, proto-writing, and other early features of urban civilization. The Bronze Age is the second principal period of the three-age Stone-Bronze-Iron system, as proposed in modern times by Christian Jürgensen Thomsen, for classifying and studying ancient societies. An ancient civilization is defined to be in the Bronze Age either by producing bronze by smelting its own copper and alloying with tin, arsenic, or other metals, or by trading for bronze from production areas elsewhere.
The Iron Age
The Iron Age is the final epoch of the three-age system, preceded by the Stone Age (Neolithic) and the Bronze Age. It is an archaeological era in the prehistory and protohistory of Europe and the Ancient Near East, and by analogy also used of other parts of the Old World. The three-age system was introduced in the first half of the 19th century for the archaeology of Europe in particular, and by the later 19th century expanded to the archaeology of the Ancient Near East. It is defined by archaeological convention, and the mere presence of cast or wrought iron is not sufficient to represent an Iron Age culture; rather, the term “Iron Age” implies that the production of carbon steel has been perfected to the point where mass production of tools and weapons superior to their bronze equivalents become possible.
The Paleolithic age is a prehistoric period of human history distinguished by the development of the most primitive stone tools and covers roughly 95% of human technological prehistory. It extends from the earliest known use of stone tools, probably by Homo habilis initially, 2.6 million years ago, to the end of the Pleistocene around 10,000 BP. During the Paleolithic period, humans grouped together in small societies such as bands, and subsisted by gathering plants and fishing, hunting or scavenging wild animals. The Paleolithic is characterized by the use of knapped stone tools, although at the time humans also used wood and bone tools.
In archaeology, the Mesolithic is the period between Paleolithic and Neolithic. The term “Epipaleolithic” is often used for areas outside northern Europe, but was also the preferred synonym used by French archaeologists until the 1960s. Mesolithic has different time spans in different parts of Eurasia. It was originally post-Pleistocene, pre-agricultural material in northwest Europe about 10,000 to 5000 BCE, but material from the Levant (about 20,000 to 9500 BCE) is also labelled Mesolithic.
Modern history, the modern period or the modern era, is the linear, global, historiographical approach to the time frame after post-classical history. This view stands in contrast to the “organic,” or non-linear, view of history first put forward by the renowned philosopher and historian, Oswald Spengler, early in the 20th century. The early modern period began approximately in the early 16th century; notable historical milestones included the European Renaissance, the Age of Discovery, and the Protestant Reformation. The late modern period began approximately in the mid-18th century; notable historical milestones included the French Revolution, the American Revolution, the Industrial Revolution and the Great Divergence. It took all of human history up to 1804 for the world’s population to reach 1 billion; the next billion came just over a century later, in 1927.