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Precambrian and Paleozoic
The Precambrian is an unranked stratigraphic unit which covers the time interval from 4600 million years ago (mya) to 542 mya, since the accretion of the Earth up intil the origin of organisms with hard body parts (outer shell or internal skeleton). Precambrian is divided into 3 eons - Hadean (informal unit), Archean and Proterozoic.
Little is known for the Hadean times. These were the times when the Moon was formed after gigantic collision between the young Earth and planet with the size of Mars, and when Earth's crust and atmosphere were formed. According to some recent discoveries we can assume that at some point primitive oceans were present 4400 mya and geological processes like tectonics, metamorphism, erosion and sedimentation have already started to function. The life probably had its origin during the Hadean.
The oldest fossil evidence of life on the planet is Archaen in age - 3500 million years old stromatolites. The only life forms during this eon were prokaryotes (single cell organisms without cell nucleus) like bacterian, cyanobacteria (the first photosynthesing organisms) and others. During this period of time, the first bigger continental blocks appeared and later consolidated forming the first supercontinent, called Ur, some 3000 mya.
The Proterozoic is characterized by the evolution of eykaryote organisms and dramatic changes in Earth's climate and atmosphere composition. Oxygen levels elevated leading to change in the atmosphere and hydrosphere. During this eon the planet faced the most severe ice ages in its history - glaciers covered most, if not all of Earth's surface, reaching almost to the equator. Towards the end of the Proterozoic the multicellular organisms appeared. They underwent rapid evolution at the beginning of the Paleozoic.
Paleozoic era, or the era of ancient life, spans from 542 to 251 mya. The era started with the so-called "Cambrian explosion" and ended with the biggest mass-extinction ever. During the Paleozoic, Earth went trough many changes. This was the time when life came out of the water and spread onto dry land - first, plants invaded coastal and continental environments during the Silurian, shortly after that followed by the animals. Actually, the first terrestrial animals, the arthropods from the late Ordovician, preceeded the first fully terrestrial plants. Climate was always changing, mostly warmer than today's, but Paleozoic was also the time of some of the biggest ice ages in post-Precambrian times - the late Ordovician, Carboniferous and Permian glacier phases, when major parts of the south continent Gondwana were covered by glaciers. The Proterozoic supercontinent Rodina fell apart in the beginning of the Paleozoic, forming one big continent, called Gondwana, located mostly south from the equator, and many smaller continental blocks north from it. Towards the end of the Carboniferous period (almost) all continental blocks gathered again to form a new supercontinent - Pangaea. Carboniferous was a period of extensive forestation which led to the forming of most coal beds in Europe and North America. At that time the oxygen levels reached their highest levels in the history of Earth - over 30%. Amniotes, the most diverse group of tetrapod vertebrates, appeared in the Carboniferous. In the next period, the Permian, the two major groups of amniotes have already evolved - the diapsids (the clade that includes lizards, snakes, crocodiles, birds and many more extinct groups of animals) and the synapsids (the group leading to mammals). In the end of the Permian, about 90% of all plant and animal life of the planet, died out.
For information on the different geochronologic and stratigraphic units and their duration, please visit the site of the International Commision on Stratigraphy - http://www.stratigraphy.org/.
Planet Earth, some 4400 mya. This artwork shows the extensive volcanism with global distribution typical for the time, and the large amount of gases released in the still forming atmosphere. The big, red to brown, extraterrestrial body in the skies is the newly formed Moon. Media: Watercolours Done: 2009
Typical landscape for the Cryogenian period, 800 mya. This is view from the tropical coasts of the supercontinent Rodinia, which existed during the Neoproterozoic era. Back then, thick glaciers covered almost the entire globe, even at the equator. This extreme ice age is known among the geologists like "Snowball Earth". Media: Watercolours Done: 2009
This artwork depicts typical fossil fauna found in the layers of the Burgess shale formation, in Canada. Shown here are the apex predator - Anomalocaris canadensis (primitive arthropod) (top), it's close relative - Hurdia victoria (middle), and Pikaia gracilens (down) which, although there is much debate on this subject, may be ancestor to all vertebrate animals, including us. These animals lived in the warm, shallow seas of the Cambrian period, about 500 mya. Media: Watercolours Done: 2009
D. terrelli is gigantic, 10 meters long, meat-eating placoderm. It lived 380-360 mya, towards the end of Devonian period. Media: Pencils Done: 2008
This animal is one of the first four-limbed vertebrates (tetrapods) to crawl onto dry land, though it was still predominatly aquatic dweller. Ichthyostega inhabited the late Devonian swamps of what's now Greenland, some 360 mya. Media: Pencils Done: 2009
Cladoselache fyleri is an extinct shark, that lived in the late Devonian period. It was a swift predator, about 2 meters long, contemporaneous to the much bigger Dunkleosteus. These two recontructions show the two possible ways of depicting bony structures on the shark's back. Media: Pencils Done: 2010
Tullimonstrum gregarium is a strange soft-bodied invertebrate animal from the Late Carboniferous (Pennsylvanian) of USA (Illinois). Its phylogenetic relationships with other animalian groups are uncertain due to its characteristics some of which are not observed in any other of the known group. The rice-shaped shells (the proper term here is tests) seen all over the sea floor are fusulinid foraminiferas. Media: Ink Done: 2011
Hamiltonichthys mapesi is a shark from the late Carboniferous of Kansas. Media: Pencils Done: 2010
Surviving has always been tough challenge, even in the early Permian. Here, the meat-eating synapsid Dimetrodon (left) is attacking one of the first herbivorous synapsids - Edaphosaurus (right). Although they look quite similar, these animals are not that closely related to each other. Not long ago both of them, along with their relatives were united as pelycosaurs - members of the group Pelycosauria. The exact function of the sail-like structures remains unknown. Media: Pencils Done: 2008
Media: Pencils Done: 2010
Glaucosaurus megalops is a synapsid from the early Permian of Texas. It's probably a close relative of the well-known "pelycosaur" Edaphosaurus. What's known from Glaucosaurus is almost complete skull therefore this reconstruction is highly speculative. Media: Pencils Done: 2012
This is a freshwater shark that lived during the Permian period. It reached about 3 meters in lenght and was an apex predator in freshwater ecosystems. This reconstruction is based on juvenile individual. Media: Pencils Done: 2012
This is reconstruction of the strange looking Permian synapsid Cotylorhynchus romeri. Despite its sauropsidian (reptilian) look this animal is more closely related to mammals than to any modern sauropsid. Cotylorhynchus first appeared in the early Permian and lived up intil about 265 million years ago. Media: Pencils Done: 2012
Two male Estemmenosuchus mirabilis are fighting during the mating season. These animals are omnivorous therapsids (the group which gave rise to mammals) from the middle Permian of Russia. Media: Ink Done: 2008
Inostrancevia is a gorgonopsid therapsid that inhabited the territory of nowdays Russia. It lived 251 mya, close to the end of the Paleozoic era. This animal was one of the biggest carnivorous animals of its time. Media: Tempera on canvas Done: 2008