Earth's History
The word "Precambrian" means "before the Cambrian" as it refers to rocks predating the Cambrian period. The term was popularised by Charles Darwin in his book "On the Origin of Species". The Precambrian lasted for about 4 billion years—nearly 90% of Earth’s existence —ending with the so-called "Cambrian Explosion". It is divided into three eons: Hadean, Archean, and Proterozoic.
Hadean 4.6 - 4 billion years ago
It’s the oldest period of the Earth’s history: it includes the formation of the Earth itself and its moon. For much of the Hadean, the Earth’s surface was covered by lava. By the end of the eon first minerals and rocks had formed. The atmosphere was mostly composed of a mixture of volcanic gases and some water vapour, and it lacked oxygen.
Archean 4.0 - 2.5 billion years ago
During the Archean, first oceanic crust and later the first micro-continents were formed. When temperatures started to drop, water vapour began to condense, leading to the formation of seas and oceans. The first oxygen in the atmosphere was a product of photolysis (light-driven breakdown of water molecules into hydrogen and oxygen). About 3.7 billion years ago, one of the first recorded living organisms — blue-green algae (cyanobacteria) — began to photosynthesize and pump more oxygen into the atmosphere.
Proterozoic 2.5 billion - 541 million years ago
At the start of the Proterozoic, increased levels of atmospheric oxygen led to the formation of the ozone layer. In the shallow seas at the continental margins, early life flourished: stromatolites became a common sight on submerged shelves, with the first organisms containing a nucleus (Eukaryotes) appearing about 2.1 billion years ago. Traces of the first multicellular life also come from the Proterozoic.
Paleogeography
The early continents of the Archean were small. With volcanism weakening about 2.5 billion years ago, the crust became thicker and more stable. It was probably when the tectonic movement, similar to the one happening today, started. The collisions of the microcontinents paved the way for the formation of the first mountain ranges. Around 2 billion years ago, the existing landmasses came together to form the first known supercontinent, Columbia, which broke apart about 1.5 billion years ago. At the end of the Precambrian, the continental blocks reunited two more times: with the supercontinent Rodinia, between 900 and 600 million years ago; and Pannotia, just before the start of the Cambrian.
Climate
Thanks to the isotopic studies of rocks, we can determine the temperatures prevailing in prehistory. For much of the Hadean, the surface of the Earth was in a liquid state, so its temperature must have exceeded 1000°C. As time passed, the Earth cooled, and the temperature gradually decreased. At the end of Hadean, it reached about 200°C, falling to about 50°C in Archean. At the start of the Proterozoic, the first global glaciation happened. Another similar event took place about 600 million years ago, right before the end of the Proterozoic. At that time, almost entire planet froze in an event nicknamed “Snowball Earth”.
Do you know that...
The age of the Earth was estimated in 1956, based on dating meteorites, like the Canyon Diablo meteorite.
The first period of the Phanerozoic, Cambrian, was established by British geologist Adam Sedgwick in 1835. Its name comes from the province of Cambria, located in North Wales on the British Isles.
Paleogeography
The beginning of the Cambrian saw the breakup of the supercontinent Pannotia into smaller continental blocks: Gondwana, Laurentia, and Baltica.
Around the equator on the continental shelves, carbonate rocks and evaporites were deposited. More north and south of the equator, up to the polar, sands were more dominant. Clays formed in the ocean depths. At the end of the Cambrian, the tectonic movements led to the beginning of the Caledonian orogeny.
Climate
The early Cambrian was relatively cool, but not cold enough to form new ice sheets. As the temperature rose, the remnants of the Precambrian glaciers melted, leading to large areas of continents being flooded. Numerous warm seas formed, flourishing with life.
Life on Earth
"The cambrian explosion"
The flooding of the continents, changes in water chemistry, and increase in oxygen levels initiated the diversification of life in the Cambrian seas. On the other hand, there was very little life on the land, limited mostly to algae mats on the banks of water bodies.
Skeletons
Animals gained the ability to produce mineral skeletons —carbonate shells, chitin carapaces, and other hard parts. The skeleton made it possible for animals to develop more advanced and complex body structures and increase in size. It also protected them against damage and predators, and after death, were more easily preserved as fossils.
Cambrian reefs
The Cambrian reefs were formed by extinct archaeocytes, animals similar to sponges. These reefs were inhabited by early arthropods, molluscs, brachiopods, and echinoderms. The most striking of these were the chitin-armoured arthropods, trilobites.
Chordates
Most of the main groups of animals appeared in the Cambrian, representatives of which live to this day. Among them were chordates, ancestors of vertebrates, which include us.
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Cambrian saw the first appearance of predators (one of the largest being Anomalocaris), starting an arms race between the predators and the prey.
In 1879, Charles Lapworth gave name to a new geological period after a pre-Roman tribe of Ordovices in Wales.
Paleogeography
In the Ordovician, the northern hemisphere was covered almost entirely by a vast ocean. Most of the land was concentrated close to and south of the equator.
Most of today's landmasses (southern Europe, Africa, South America, Antarctica, and Australia) have been a part of Gondwana since the Cambrian. This mega-continent migrated south, where it eventually arrived at the end of the Ordovician.
Other landmasses were separated by oceans, such as the Iapetus Ocean, which separated continents of Baltica, Avalonia and Laurentia. As it closed, the continents converged, starting the Caledonian orogeny.
Climate
For most of the Ordovician period, Earth had a temperate and warm climate. But, with Gondwana reaching the South Pole, extensive ice sheets began to form, starting the first Paleozoic ice age.
Life on Earth
Great Ordovician Biodiversification Event
The large, warm, shallow seas helped the diversification of marine life. Nautiluses, mussels, brachiopods, and snails experienced a boom in the evolution of new species and in numbers. Solitary horn corals (Rugosa) and hexagonal colonial corals (Tabulata) were the Ordovician reef-forming organisms. This unprecedented period of life’s on Earth history has been nicknamed "The Great Ordovician Biodiversification Event".
Graptolites
Graptolites appeared in the Ordovician, and they were one of the first animals to thrive in open sea environments. They were hemichordates related to today's Pterobranchs, small worm-shaped animals. Graptolites are important index fossils.
Colonization of land
The oldest spores discovered so far, indicating the plant colonisation of land, date back to the early Ordovician. They likely belonged to the relatives of modern mosses. Slightly younger are the traces of fungal hyphae. The oldest trace fossils of animals on land, likely distant relatives of horseshoe crabs and arachnids, also come from the Early Ordovician.
Vertebrates
Individual bones and soft tissue traces were recovered from Cambrian rocks, but the oldest complete unequivocal skeletons come from the Ordovician. They belong to a jawless armoured fish commonly known as ostracoderms, although their taxonomic placement is still disputed. A typical Ordovician fish had a head composed of large bony plates and usually lacked paired fins.
The great extinction
The glaciation that took place at the end of the Ordovician was short-lived yet extensive. The changes in sea levels, as a consequence of that glacial period, led to mass extinction, in which about 85% of the species vanished.
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The Ordovician glaciation caused a drop in sea levels of about 50 meters.
The Silurian was described in the 1830s by Englishman Sir Roderick Impey Murchison after rock formations in South Wales. The period was named after a Celtic tribe, the Silures, that lived around regions of the current Welsh-English border.
Paleogeography
Throughout the Silurian, the Gondwana continent continued to move southward. Present-day South-West Africa was located near the South Pole, while the smaller continents gathered around the equator and the tropics.
The end of the Silurian is marked by the collision of the Laurentia, Baltica, and Avalonia continents and the closure of the Iapetus Ocean between them. A new large continent was created, known under various names: Laurosia, Laurussia, Euroamerica, or the "Old Red" continent (after the colour of the sandstone formed in that region). This event is called the Caledonian Orogeny, and it led to the formation of mountain ranges stretching through Europe, Greenland, to North America.
Climate
The Silurian was a transitional period between the cold Late Ordovician and the hot Devonian. The warm climate caused the melting of glaciers, which led to the rise of global sea levels.
Life on Earth
Reefs
Reefs were formed by corals, sponges (stromatoporoids), bryozoans, and coralline algae that used structural mineral substances in their cells.
Graptolites
Silurian was a time of graptolite renissance. The genus Mongraptus, a common cosmopolitan graptolite of that time, split into many species that are useful index fossils. Silurian graptolite shales are of interest to geologists looking for hydrocarbon deposits.
Origin of jaws
In vertebrates, the development of jaws was a completely new invention. They evolved from gill arches and took on new functions. Hard mouthparts were more efficient for feeding and began to displace more primitive types. The oldest vertebrates with jaws were armoured fishes.
Life on land
The first vascular plants, rhyniophytes, appeared at the beginning of the Silurian. They did not have leaves, roots, the ability to expand in width, or the ability to conduct water via the stem. Early terrestrial floral communities homed the early faunal land life. Early terrestrial animals were millipede-like animals that fed on dead organic matter, predated on by relatives of modern centipedes.
Do you know...
The sea level in the Silurian was 200 meters higher than today.
The establishment of Devonian came with a debate among numerous 19th-century European geologists. In the end, Sir Roderick Murchison and Adam Sedgwick in 1839, established the new period, named after Devonshire, where the best rock exposures of that period are found.
Paleogeography
The early Devonian saw the last phases of the Laurussian (Euroamerica) formation. During the erosion of the new mountain belt, the new rock material was deposited in depressions and transported by rivers to the seas. Laurussia and Gondwana began coming together and closing the Paleo-Tethyan and Rheic Oceans between them.
Climate
The Devonian climate was generally warm and dry, with minimal differences in temperature between the equator and the poles. There was a brief, but extensive, glaciation period at the end of the Devonian.
Life on Earth
Reefs
The Devonian saw the intensive development of reefal environments, the largest in all of Earth’s history. They were built predominantly by encrusting red algae and stromatoporoids, with corals being a minor group.
The reign of fishes
The Devonian period witnessed an explosion in fish diversity, especially in jawed fishes: armoured (Placoderms) and cartilaginous (Chondrichthyes). Lobe-finned fishes were also common. They were the ancestors of terrestrial vertebrates.
Terrestrial vertebrates
The oldest footprint traces of vertebrates date back to 390 million years ago and were found in the Świętokrzyskie Mountains in Southern Poland. These prints were made by animals that probably measured up to 2 metres and had appendages with at least six fingers.
The green revolution
In the Devonian first forest-like ecosystems evolved, with some species reaching nearly 30 m in height. Deeper root systems stabilised the ground and produced organic compounds, which sped up the process of chemical weathering of rocks. The rapidly developing vegetation absorbed carbon dioxide, reducing its presence in the atmosphere and increasing atmospheric oxygen content. This atmospheric gas turnover led to climate change in the Late Devonian, which led to cooling and glaciation.
The great extinction
The onset of glaciation and alternation in sea and ocean chemistry (caused by extensive weathering) led to an environmental change and a consequent mass extinction event. Many species of brachiopods, trilobites, graptolites, and fishes went extinct, including all armoured fishes and most of the cartilaginous.
Do you know...
The largest known arthropod in the history of life lived in the Devonian period - the eurypterid Jaekelopterus. It could reach over 2.5 metres in length. The Pterygotus was not much smaller, also measuring over 2 metres.
The Carboniferous was established in 1822, based on geological observations from England and Wales. Its name derives from the Latin word for coal (carbon). Although the Carboniferous period is known for some time, the dating of its base remains debatable.
Paleogeography
The main phases of the Variscan (Hercynian) orogeny took place in the Carboniferous. As a result, all the continental landmasses collided to form a new single supercontinent, Pangea, and the massive mountain ranges called Variscides (or hercinids) marked the collision zones. These ranges stretched through Europe, Africa, Asia, Australia, and North America. Traces of that orogenic event can be found in the Polish Sudetes and the Holy Cross Mountains.
Climate
The early Carboniferous was warm and relatively humid around the equator. Later, the climate began cooling, forming an extensive glacial cover over the South Pole at the end of the period.
Life on Earth
Life in the sea
At the beginning of the period, the last graptolites went extinct, and the previously lush reefs became small and species-poor. On the other hand, the diversity of echinoderms, and among them, crinoids, rose significantly. There were so many of them that their skeletons became material for new kinds of rocks.
Fishes diversity
The Carboniferous is the golden age of sharks, which took over the mantle of apex predators after armoured fishes, which went extinct at the end of the Devonian. Lobe-finned fishes reached extreme sizes, like Rhizodus, the largest known freshwater fish, reaching up to 7 metres in length.
Giant invertebrates
The characteristic component of the Carboniferous forest fauna were the huge invertebrates, like metre-long scorpions or two-metre-long millipedes like Arthropleura. These giant sizes could have been reached likely thanks to an increased amount of oxygen in the atmosphere.
Amniotes
The first amniotes appeared in the Carboniferous. They are a group of vertebrates that undergo embryonic development that includes several membranes surrounding the embryo for protection, gas exchange, and metabolic waste disposal. This adaptation enabled reproduction on land without the need for nearby water, unlike, e.g., amphibians. The ability to lay shelled eggs allowed vertebrates to spread globally. The ancestors of mammals (Synapsida) and reptiles (Sauropsida) evolved from amniotes.
Do you know that...
The wingspan of a dragonfly Meganeura reached 60-70 centimetres.
The Permian is the youngest period of the Paleozoic. Established by Sir Roderick Murchison in 1841, based on rocks from the Ural Mountains in Russia.
Paleogeography
Permian saw the final stages of the Pangaea supercontinent formation. The single continent was surrounded by a giant ocean, Panthalassa. The Pangea was C-shaped. Its north contained the lands of today's Europe and Asia. The Americas and Africa formed its centre, and India, Australia, and Antarctica were in the south. To the east of the continent was the Tethyean Ocean. Soon after the formation of Pangea, tectonics came into motion. New rifting paved the way for the eventual supercontinent breakup in the next period.
Climate
At the beginning of the Permian, the Earth was cool. Intensive warming began in the middle of the period, and droughts prevailed in the centre of the continent. We can find records of that period in the red-coloured Permian deposits.
Life on Earth
Life in the sea
We know little about what was happening in the depths of the Panthalassa Ocean but have little more information on the marine ecosystems surrounding the continent. The reef builders at the time were sponges, bryozoan, and algae. The reefs were inhabited by brachiopods, molluscs, and fish.
Surviving the drought
With climate warming and the continent drying up, the humid swamps and forests that characterized the Carboniferous gave way to drought-tolerating plant communities. The land was dominated by gymnosperms and conifers, which could retain moisture, enabling survival in dry conditions. In that period, cycads and ginkgos appeared.
The new herbivores
The Permian saw the appearance of numerous pioneering herbivores. The larvae of insects feed on the leaves and roots of plants. Other key herbivores included large reptiles like Pareiasaurs, which could reach up to three metres in length.
Mammalian ancestors
Within synapsids, which evolved from the first amniotes in the Carbonierous, a group called therapsids emerged. Therapsids were the ancestors of mammals, with a primitive version of endothermy enabling a nocturnal lifestyle, allowing them to fill niches inaccessible to cold-blooded reptiles.
Mass extinction
The mass extinction at the end of the Permian ended the reign of the typical marine Paleozoic fauna. It is estimated that up to 85% of all genera of animals and plants disappeared, including all eurypterids, trilobites, and most of the brachiopods, crinoids, and ammonites.
The extinction might have been caused by extensive volcanism, which caused rapid climate change and led to ecological catastrophe.
Do you know...
Thanks to Pangea life could roam freely across the continent. As a result, we find fossils of the same animals across different continents.
The Triassic is the oldest period of the Mesozoic. The name derives from the Greek word triás, meaning "triad", used first in 1834 by a German geologist Friedrich von Alberti.
Paleogeography
In the Triassic, a single landmass, Pangea, dominated the global Panthalassa superocean. Pangea's central area sat around the equator, while its ends reached the poles. At the end of the period, Pangea's started to disintegrate.
Climate
With all landmasses connected, oceanic waters were freely exchanged between equatorial and polar regions. As a consequence, the average temperatures at the poles were much higher, preventing the formation of extensive ice caps as seen today. The centre of Pangea was hot and dry.
Life on Earth
Life in the sea
Planktonic and nektonic organisms evolved rapidly in marine environments, especially cephalopods such as ammonites and belemnites. Simultaneously, reef-forming organisms vanished in a so-called "Triassic reef gap" interval.
Marine vertebrates
Not many groups of fishes survived the Permian extinction, so during the Triassic, the existing species weren't the most diverse. The seas were also inhabited by marine reptiles, including sauropterygians, which include nothosaurs, placodonts, plesiosaurs, and ichthyosaurs.
Giant amphibians
The early Triassic river and lake environments were dominated by amphibians. Some reached giant proportions, such as Mastodonsaurus, which could reach up to 4 to 6 metres in length. Metoposaurus from Krasiejów, near Opole, was two metres long. Some amphibians evolved to tolerate colder conditions and settled in the temperate forests of Antarctica. Most of them disappeared by the Middle Triassic, outcompeted from their niches by crocodilian ancestors.
Archosaurs and the first dinosaurs
The hot and dry climate favoured reptiles, including archosaurs, which diversified rapidly in the early Triassic, including pseudosuchians, ancestors of crocodiles, and the group from which dinosaurs, birds and pterosaurs originated. Dinosaurs likely made their first appearance in the Middle Triassic.
Synapsids and the first mammals
The ancestors of mammals (known as synapsids) were badly hit by the Permian extinction. Only a few lineages survived until the Mesozoic, but even these did not last long. Among the survivors were cynodonts, which evolved rapidly in the Triassic and gave rise to modern mammals.
Plants
The terrestrial landscape was dominated by gymnosperms, especially conifers. Ginkgo biloba, cycads, and bennettitales were common. At the end of the Triassic, ferns became a rarity.
Mass extinction
The Triassic concluded with a mass extinction that hit both marine and terrestrial life. In the seas, all conodonts went extinct, as did all goniatites of the ammonite clade, as well as other groups. On land, mammalian relatives and many archosaurs also died off.
Do you know...
In the early Triassic, temperatures in the tropical regions were so high that very few organisms could survive there.
The term Jurassic comes from the word “jura”, which in Celtic means "overgrown mountain.” It was assigned to a mountainous region on the French-Swiss border. Alexander von Humboldt called the rocks found in that region Jurassic limestones. Years later, the word Jurassic was adopted as a new geological period.
Paleogeography
The supercontinent Pangea progressed to break up in the early Jurassic. The central part of the continent saw the formation of several rift zones, one of which later became the Atlantic Ocean.
In the Middle Jurassic, the still-connected South America and Africa began to separate from North America, opening up the Gulf of Mexico. The Tethyean Ocean reached its full size in the Jurassic.
Rifting also took place in the south, breaking the former Gondwana into two blocks: African-American and Australia, and Antarctica with the Indian Peninsula (Deccan), beginning to form the Indian Ocean.
Climate
The Jurassic climate was warmer than today, with less seasonal variation. The tropical and subtropical climates extended further north and south, with temperate climates at the poles.
Life on Earth
Life in the sea
The fracturing of Pangea created new coastal lines. The lack of glacial caps resulted in high global sea level, creating shallow seas in lower continental areas. New predators appeared in these seas, such as crabs, snails, sea urchins, and various vertebrates. This forced the prey to develop new survival strategies, like buddowing in sediments or sharp spikes. The rapidly evolving ammonites later became excellent index fossils, helping to correlate rocks. The reef builders were mussels called rudists, sponges, polychaetes, and algae.
Archosaurs and the great amphibian extinction
On land, dinosaurs diversified and became very common in the Jurassic. During that time, the largest animals to ever grace the lands — sauropods — were numerous. The large herbivores were predated on by new large carnivores such as Allosaurs.
At the same time, their sister clade, Pseudosuchians, was outcompeted and had to find new ecological niches. They moved to water environments previously ruled by amphibians. Reptiles invading the aquatic niches led to the extinction of most large amphibians.
First birds
The first avians evolved from small, feathered dinosaurs. To achieve active flight, early birds reduced body size and weight thanks to hollow (pneumatic) bones and replacing teeth with lighter beaks. Forms almost identical to modern birds appeared by the end of the Jurassic.
Jurassic mammals
The Jurassic mammals were usually omnivorous and herbivorous, carnivores were rare. By the Middle Jurassic, mammals had become viviparous (giving birth to live young), paving the way for all modern placentals. One of the oldest known representatives of placentals is a tiny Juramaia.
Flora
A lot of the land was covered by conifer forests. Numerous new species of araucarias (monkey puzzle trees) and deciduous gymnosperms like cycads and ginkgo appeared. In subtropical and tropical areas, alongside cycads and bennettitales (which experienced their maximum diversity in the Jurassic), ferns releasing seeds and spores also became an important component of the flora.
Do you know...
Forest fires were frequent in the Jurassic, leaving a large amount of charcoal in Jurassic rocks.
The Cretaceous was the last and longest period of the Mesozoic, with a duration of 79 million years. It was established by Jean d'Omalius d'Halloy, a Belgian geologist, based on chalky rocks in Western Europe, named after the Latin word "creta" (chalk).
Paleogeography
By the end of the Cretaceous, the continents started to resemble their current, familiar-for-us shapes. Gondwana broke up. South America, Antarctica, and Australia migrated away from Africa, opening up the South Atlantic Ocean and expanding the Indian Ocean. Only the Deccan (Indian Peninsula) had not yet merged with Asia, and Australia was still connected to Antarctica.
Climate
The Cretaceous was warm, with little temperature variance between the equator and poles. Cold spells were brief, with the sea levels reaching the highest levels ever recorded in the Phanerozoic.
Life on Earth
Marine vertebrates
Vertebrates thrived in the seas. Shark species were very numerous, while other modern fish groups, like sturgeons, appeared. Cretaceous seas were still ruled by reptiles such as ichthyosaurs, plesiosaurs, and mosasaurs.
Kings of the sky
All modern birds belong to the group Euornithes ("true birds"). Hovewer, the Cretaceous sky and land were also populated by animals related to true birds. Some resembled modern birds, while others were completely different and unique. By the end of the Cretaceous, that diversity had disappeared. Numerous Euornithes died out - the modern birds come from a few descendants that survived the mass extinction.
The skies were full of reptiles - pterosaurs. At the time, they were kings of the skies, being the largest animals that have ever taken to the air. The largest known pterosaur had a 10-metre wingspan.
Diversity of dinosaurs
The Pangea breaking up forced dinosaurs to split into isolated populations, leading to strong diversification and leading to appearance of groups characteristic for each continent. Most sauropods died at the beginning of the Cretaceous, those that survived reached unprecedented sizes.
Flower revolution
The oldest fossils of flowering plants (angiosperms) come from the Cretaceous rocks. Flowering was a novel way of reproducing in which plants develop a symbiosis with insects to disperse pollen in exchange for sweet nectar. This strategy proved to be extremely effective, as angiosperms today dominate the world of plants.
The K-Pg extinction
About 66 million years ago, another mass extinction took place. This catastrophic event had an impact on all ecosystems and taxa globally. The most widely accepted cause was a bolide hitting the Yucatan Peninsula and extensive volcanism on the Indian Peninsula.
Do you know…
In the Cretaceous, certain ammonites, like Didymoceras, created shells in unusual shapes
The formerly used period called "Tertiary" was split into two smaller periods: Paleogene and Neogene. The term Paleogene was first used by the German geologist C. F. Naumann in 1866.
Paleogeography
In the Paleogene, the continents were close to their current-day positions. A collision between the Deccan (Indian Peninsula) and mainland Asia resulted in the Himalayan orogen. Africa migrated north, pressing onto Europe, forming the Alpine mountain chain, which includes the Carpathians.
South America also shifted northwards. Australia separated from Antarctica, opening the Drake Strait and forming a pathway for the Antarctic Circumpolar Current, thermally isolating Antarctica and causing extensive glaciation that lasts until this day.
Climate
After the warm, humid Cretaceous, the climate became cooler and drier, with occasional temperature spikes. The Antarctica glaciation around 34 million years ago accelerated this cooling trend.
Life on Earth
The reign of the mammals
The end-Cretaceous extinction led to the disappearance of most of the larger animals. Mammals, freed from the competition and predation of dinosaurs, started filling in vacant ecological niches. They increased in size and diversity, taking over land, water, and the skies.
Back to the water
Three groups of mammals independently returned to the water. Cetaceans evolved from ungulate carnivores. Dugongs (sea cows) are the most closely related to elephants and hyraxes, while pinnipeds are related to bears and weasels.
Giant birds
Large flightless birds appeared in the Paleogene: predatory Phorusrhacids ("terror birds") as part of Cariamiformes, massive herbivorous Gastornis and Dromornis with powerful beaks. Giant birds, resembling modern albatrosses, had wingspans of 6 metres!
From tropical forests to dry steppes
At the start of the Paleogene, the land was covered with lush forests and swamps. With climate cooling and drying, the forests shrank and were replaced by grassy steppes and new types of animals suited for the new environment.
Did you know ...
The largest land mammal, Paraceratherium, lived at the end of the Paleogene.
The oldest record of primates dates back to 57 million years, barely 9 million years after the extinction of dinosaurs.
The term Neogene came about in 1853 from the Austrian palaeontologist Moritz Hörnes, who combined the existing Miocene and Pliocene into one period based on fossil similarity.
Paleogeography
The distribution of continents was almost similar to the modern one. The Isthmus of Panama formed, connecting the two Americas. The Deccan, forming the Indian subcontinent, still pushed into Asia, raising the Himalayas. The Alpine orogeny was still ongoing in Europe.
The sea level was low, forming land bridges between Asia and North America and Africa and Eurasia. 6 million years ago the Mediterranean Sea had completely dried out.
Climate
The average temperatures in Neogene were higher than today, especially at the beginning of the period. Later, the climate cooled rapidly, ending the Neogene with the onset of Pleistocene glaciations.
Life on Earth
Terror of the seas
The largest shark and one of the largest predators on record - Megalodon - haunted Neogenic seas. We do not have its skeletal remains, but looking at its huge teeth (up to 18 cm!), it is estimated it could be over 10 metres long.
Meadows and steppes
Environments like meadows and steppes dominated the Neogene, occupied by herds of grazers with stomachs modified to digest grasses. Open spaces favoured animals that could run fast to avoid predation, which led to the evolution of animals like horses.
Hominids
Africa drying up and developing extensive savannahs exerted new adaptations among primates, leading to an upright posture and modifications in jaws, teeth, and behaviour. Human, gorilla, and chimpanzee common ancestor lived 8 to 4 million years ago. The first representatives of the genus Homo appeared about 2.8 million years ago.
The great migrations
Land connections between previously isolated continents allowed animals to migrate. The new arrivals frequently outcompeted native residents, leading to local extinctions. As an example, the southward migrating predators from North America (raccoons, wolves, big cats, and bears) displaced and drove predatory marsupials to extinction in South America.
Do you know ...
Most of the Polish lignite (brown coal) formed in that period, about 20 million years ago.
Back in the mid-17th century, the Italian geologist Giovanni Arduino proposed the first stratigraphic divisions. The only division that is still in use from that old system is the "Quarto ordine" (The Fourth Order, or Quaternary). This period is divided into the Pleistocene and the Holocene (in which we're currently living).
Paleogeography
At the start of the Quaternary, the distribution of the continents was nearly identical to the present. However, the continents continue to move, which we can monitor using modern technologies. The Americas are migrating westwards away from Europe and Africa at a rate of 2.5 centimetres per year, expanding the Atlantic. The Indian Peninsula continues to push northwards at a speed of about 5 cm per year, continuously raising the Himalayas and Mount Everest. Australia is the fastest-moving of the continents, moving northwards at 7 cm per year.
Climate
The Quaternary is characterised by a relatively cool climate with cyclical cooling and warming periods. The Pleistocene saw an increase in rainfall in the intertropical zone. Poles have been covered with ice since the beginning of the Quaternary, with polar ice sheets growing significantly during Pleistocene glacial periods.
Glaciations in Poland
The Pleistocene experienced periods of cooling (glaciations), separated by warmer periods known as interglacials.
The ice sheet covered Poland for the first time 1.2 million years ago and returned to the area many times, partially or fully covering the region. The last Polish glacial episode ended 11 thousand years ago, marking the end of the Pleistocene and the beginning of the Holocene, which is considered an interglacial episode in the ongoing Ice Age.
Life on Earth
Flora
Steppes and glacial tundras, dominated by grasses and dwarf trees, were common in the cold climate zone. During interglacials, the tundra moved northwards and was replaced with multi-species mixed forests, swamps, and meadows with many extant plants.
The megafauna of the Pleistocene
Vast, empty steppes were the roaming grounds for huge animals such as mammoths (Eurasia) and mastodons (North America), woolly rhinos, wild cattle (aurochs), large cats, and marsupials (in Australia). Most of these large mammals died out by the end of the Pleistocene, replaced by the species we know today.
First modern people
With the gradual drying and steppe formation in Africa in the Pleistocene, the evolution of modern humans began. Different lines of hominids appeared and often lived beside each other. One of these lineages, Homo erectus, lived around 300-200 thousand years ago and eventually led to the evolution of our species.
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The Baltic Sea began with the disappearance of the Scandinavian ice sheet. The in-and-out glaciations meant that the Baltic changed several times from lake to sea before gaining its present form.
A woolly rhino could reach heights of two metres and be five metres long, weighing about 3.5 tons
