Chapter Six

Geology

6.1 One theme running throughout this story is how certain individuals have changed the way the rest of the world understands and appreciates Nature thanks to their intelligence, original insight, and dedication. A related theme is how Western understanding and appreciation of Nature has evolved over the past 500 years from one which was largely determined by the single most influential book of the period, the Bible. The history of Geology during this time richly illustrates these two themes.

6.2 One of the first inspirations for such investigating the history beneath the soil was to prove the Biblical view of the world and its history, and in particular the existence of Noah’s Great Flood. Usher’s dating of the world and 16XX Whitstone view of the world. But enthusiasm to find such fossil proof led to the discovery of great quantities of fossils which raised more questions than delivered answers, and Whitstone view was to be challenged by Frenchman Clerc in 1749.

6.3 Geology was not formally recognised as a separate branch of science until De Saussure coined the word geology. His exploration of the Alps and the mysteries they embodied – how were they formed, when were they formed, why are they composed of these particular layers of rocks led him to realised that there was literally a whole world of knowledge to be explored to answer such questions. The word came to be accepted though only after publication in Diderot’s monumental encyclopaedia in 175X.

6.4 Thanks to the work of the likes of de Saussure, Diderot, and their Academie Française the firm national institution devoted to the furtherance of scientific inquiry (predating the British Royal Academy by XX years) France was at the forefront of investigation into Natural Sciences. The Natural History Museum in France was the world’s premier institute for such research and they created the world’s first teaching post specifically for Geology.

6.5 One of the key geological puzzles of the age, and one that de Saussure wrestled with during his expeditions to the Alps and many other mountain ranges, was how rock was laid down in the first place, particularly soft rocks like sandstone and limestone. The prevailing theory was that it was laid down like silt from the oceans during some time of flooding long ago – and this of course supported the idea of there having been a Great Flood and so confirmed the Biblical view of the world and that its history need not be so old. In fact a great a another French religious thinker Alfred the Great several hundred years before had noticed this curiosity that there were fish fossils at the top of mountains and was possibly the first to propose the flood theory. This idea was called neptunism from the god of water.

6.6 As more and more fossils were discovered more and more questions than answered. One central question was were these fossils of currently existing plants and animals – which would tend to support the current theory of the youth of the earth or something completely different? One scientist appointed to a junior position at the National History Museum was Georges Cuvier. He made himself an expert in paleontology studying exhaustively all the fossils in the museums’ collection. From his intimate knowledge of these fossils and the body plans of the creatures that had created them, he made a revolutionary breakthrough in understand – there were fossils of creatures that no longer existed. Not just one or two, but there were vast numbers which represented animals no longer extant. In 1812 published that a convincing theory was presented for the evidence for previous extinctions and that therefore that the earth was much older than previously thought. This insight added much greater significance to the search for more fossils to confirm or deny this theory and so to understand the movement of the earth over time.

6.7 However a rival theory arose saying that rock strata were shaped not by water but by fire, and that volcanic activity and lava flows were responsisble for the rocks layers being discovered across the world. The big difference between the two theories was the time required by each. The plutonic theory refined and developed by Hutton proposed a new view of the world, one that was in constant motion with rock layers being laid down continually but very slowly over vast periods of time, rather than as one off events of a flood or floods in not too distant history. Interestingly Cuvier whose brilliant insights and dedicated work proved the existence of vastly ancient worlds with creatures now gone extinct, was a big opponent of Hutton and later Lyell’s view of a vastly ancient world in perpetual geological motion.

6.8 And not surprisingly because no mechanism for such a gradual shifting of rock layers let alone moving around of continent had been demonstrated. This idea was to fall to Wenger to propound in 1916 and it was immediately dismissed by the scientific community and not eventually accepted until 1953 and the evidence for tectonic plates was developed.

6.9 But religious motives were not the only driver for geological exploration, the profits to be made from mining the earths resources also added a certain incentive for individuals to take up this study. And with the rise of industry and its demand for coal power to fuel its factories and steam engines, interest in finding and exploiting coal seams rose to the level of national importance. It is not therefore surprising that one of the first geological ages to be defined was the Carboniferous, (by XX in 1822) the age where the great coal seams were laid down. The name Carboniferous is derived from the Latin meaning "coal-bearing" and was coined by geologists William Conybeare and William Phillips in 1822. Based on a study of the British rock succession, it was the first of the modern 'system' names to be employed, and reflects the fact that many coal beds were formed globally during that time. There is a nice apochryphal story that the similarity of the coal seams was noted by Welsh miners who emigrated to Mississippi and found themselves working on a familiar coal seam!

6.10 Again not surprisingly it was scientists from the country that gave rise to the industrial revolution that were amongst the first to explore these ideas in a systematic way. So it was that one of the great text books was german Abraham Gottlob Werner and so it was that many of the first geological periods to be named were located by British scientist and named after sites in Britain which they explored.

6.11 William Smith first Geological map – surveyor opportunity to see rock layers and also estimate the technical engineering difficulties hidden beneath the surface based on understanding rock formations. This was the first ever map of what was beneath the surface of the earth.

6.12 The Paleozoic lasted around 300 million years from 542 to 252 million years ago. It is the longest of the Phanerozoic eras, and is subdivided into six geologic periods (from oldest to youngest): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. Five of these six periods were named by British geologists in the early 19^th century, amidst much debate and controversy. Adam Sedgwick named the Cambrian after Cambria, the Latinised form of Cymru, the Welsh name for Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits which are of exceptional preservation, where "soft" parts of organisms are preserved as well as their more resistant shells.

6.13 The next but one period, the Silurian, was first identified by British geologist Sir Roderick Impey Murchison, who was examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s. He named the sequences after a Celtic tribe of Wales, the Silures, inspired by the example of his friend Adam Sedgwick. In 1835 the two men presented a joint paper, under the title ‘On the Silurian and Cambrian Systems, Exhibiting the Order in which the Older Sedimentary Strata Succeed each other in England and Wales,’ which marked the beginning of establishing the modern geological time scale. However, as it was first identified, the Murchison’s "Silurian" series of rock strata, when traced farther afield, quickly came to overlap Sedgwick's "Cambrian" sequence, provoking furious disagreements between the two great men that ended their friendship. Charles Lapworth resolved the conflict by defining a new period including the contested beds which he called Ordovician again named after a Celtic tribe to mollify his warring friends. The next period was amicably named the Devonian after Devon, England, where rocks from this period were first studied, once again by the same pair of geologists, Roderick Murchison and Adam Sedgwick. The next but one period is the Permian so called 1841, this time by Murchison alone, after a tour of Imperial Russia, when he named it after the ancient kingdom of Permia and the present city of Perm near the Ural mountains in Siberia.

6.14 If it was the British who named the Paleozoic era from 542 to 252 Ma then it was their counterparts from Germany and France who took the lead in naming the next period, the Mesozoic, from 252 to 65 Ma.

6.14 The Triassic period which follows spans the next 52 million years up to the Jurassic in 201 Ma.   The first half was spent recovering from the previous extinction event. The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers (tri meaning "three") that are found throughout Germany and northwestern Europe—red beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstones—called the "Trias". Therapsids and archosaurs were the chief terrestrial vertebrates during this time.

6.15 The Jurassic period extends 56 million years up to 146 Ma and was named after the Jura Mountains within the European Alps, where limestone strata from the period were first identified. It was none other than Alexander von Humboldt who recognized the mainly limestone dominated mountain range of the Jura Mountains as a separate formation that had not been included in the established stratigraphic system defined by Abraham Gottlob Werner, and he named it "Jurakalk" in 1794.

6.16 The long Cretaceous period followed for the next 79 million years. The Cretaceous period got its name from the type of rock deposited along the northern shores of the Tethys Sea in a band running from what is now Ireland and Britain to the Middle East. This rock formed from the deposits of the tiny limestone skeletons of diatoms is known as chalk. The Latin for chalk is creta, so the period was named the Cretaceous. In 1822, Jean-Baptiste-Julien Omalius d’Halloy used the name ‘Terrain Cretace’ to describe the chalk strata found in France. Since these same strata were also present across the English Channel, English geologists began calling using the same term.

6.17 At the time of discovery of the Cambrian fossils it was thought that this period was the beginning of time – although the precise age in years could not then be measured. From that point as geology progressed, geologists not only established more recent history and geological periods more accurately but they moved back in time to explore the Precambrian world – which came to be known as the Archaen and Proterozoic.   Only from 1972 was a new Eon defined named the Hadean - being the period from the formation  of the earth prior to around 4 billion years ago, a time before the oldest rocks which are still in existence today.

6.18 This is also why the current Geological Timescale makes the Cambria period the pivotal period in Earth’s geological existence with all the rest of time before lumped together under one super eon Precambrian.

6.19 The age of the Earth is classified by the International Commission Stratigraphy (ICS), for the convenience of people interested in the subject, into Eons, within which are Era, within which are Periods, within which are Epochs.

6.20 The first three Eons - Hadean, Archean and Proterozoic (which collectively are known by the super-eon as Precambrian) cover a period of nearly 4 billion years from the formation of the earth and the origin of single-celled life in the oceans, up until 542 million years ago and the ‘Cambrian explosion’ – an astonishing period of accelerated evolution which saw all the 30 or so modern phyla (body forms) laid down, as well as life emerging at last from the oceans to colonize land. The current Eon, the Phanerozoic, covers the remaining half million years or so during to the present day, during which all visible life has evolved.

6.21 The first Eon began with the formation of the Earth about 4.6 billion years ago and ended 4 billion years ago. It was called Hadean after Hades, the ancient Greek god of the underworld, in reference to the hellish conditions on Earth at the time. The planet had just formed and was still very hot due to high volcanism, a partially molten surface and frequent collisions with other Solar System bodies. The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks on Earth. The Hadean atmosphere was dominated by carbon dioxide and nitrogen (in much the same ratio as in the present day atmospheres of Venus and Mars).

6.22 Archaean, the name of the next eon, comes from the ancient Greek meaning ‘beginning, or origin’. Its earliest use is from 1872, when it meant "of the earliest geological age." For a hundred years it included all the time from the formation of the Earth, until Preston Cloud came along and detached the Hadean.

6.23 Instead of being based on stratigraphy, the study of rock layers’ ‘strata’, the beginning and end of the Archean eon are defined in terms of time, beginning exactly 4 billion years ago and ending exactly 2.5 billion years ago. At the beginning of the Archaean, the Earth's heat flow was nearly three times as high as it is today, and it was still twice the current level at the transition to the Proterozoic. Volcanic activity was considerably higher than today, with numerous lava eruptions, and the resulting granitic rocks predominate throughout the crystalline remnants of the surviving Archaean crust.

6.24 The Archaean atmosphere is thought to have had little free oxygen. Astronomers think that the Sun had about 70–75 per cent of the present luminosity, yet temperatures on Earth appear to have been near modern levels after only 500 Ma of Earth's formation. The moderate temperatures may reflect the presence of greater amounts of greenhouse gases than later in the Earth's history.

6.25 The processes that gave rise to life on Earth are far from being understood, but there is substantial evidence that life came into existence either near the end of the Hadean Eon or early in the Archaean Eon. One of the first two major groups of life is named Archaea and comprises organisms capable of surviving under extreme conditions such as might have existed in the boiling depths of the oceans during that time. Biogenic carbon has been detected in zircons dated to 4.1 billion years ago in the Hadean, but this evidence is preliminary and needs validation. More solid indirect evidence of life comes from banded iron formations in greenstones that date to 3.7 billion years. The formation of banded iron deposits is thought to require oxygen, and the only known source of molecular oxygen in the Archaean Eon was photosynthesis, which implies life. The earliest identifiable fossils consist of stromatolites—accretionary structures formed in shallow water by Cyanobacteria – one of the heroes of our Story —dated to 3.5 billion years ago.

6.26 Life was probably present throughout the Archaean, but may have been limited to simple single-celled organisms lacking nuclei, called Prokaryota. There are no known eukaryotic fossils from the earliest Archaean, though they might have evolved during the Archaean without leaving any.

6.27 The following Eon, named Proterozoic from the Greek meaning ‘earlier life’, lasted nearly 2 billion years up until 542 million years ago. As is the wont for geologists this huge block of time is broken down into with the usual Greek prefixes Paleoproterozoic, Mesoproterozoic, and Neoproterozoic (old early life, middle early life and new early life).

6.28 The well-identified events of this eon were a) the transition to an oxygenated atmosphere during the Paleoproterozoic, b) several glaciations, which produced the hypothesized Snowball Earth during the late Neoproterozoic Era, and c) the Ediacaran Period (635 to 542 Ma) with the evolution of abundant soft-bodied multicellular organisms and the first fossil evidence of life on earth and the precursor to the astonishing Cambrian explosion.

6.29 One of the most important events of the Proterozoic eon was the accumulation of oxygen in the Earth's atmosphere. Though oxygen is believed to have been released by photosynthesis, thanks to our heroes the Cyanobacteria, as far back as Archaean Eon, it could not build up to any significant degree until mineral sinks of unoxidized sulphur and iron had been filled. Until roughly 2.3 billion years ago, oxygen was probably only 1% to 2% of its current level. The Banded iron formations, which provide most of the world's iron ore, are evidence of that mineral sink process. Their accumulation ceased after 1.9 billion years ago, after the iron in the oceans were oxidized, thus allowing oxygen to build up in the atmosphere.

6.30 It is believed that 43% of modern continental crust was formed in the Proterozoic, 39% formed in the Archean, and only 18% in the Phanerozoic. It is also believed that during this period, the Earth went through several supercontinent breakup and rebuilding cycles.

6.31 A supercontinent called Columbia was dominant in the early-mid Proterozoic around 1.5 billion years ago (1.5 Ga) but not much is known about continental assemblages before then. The current most plausible theory is that prior to Columbia, there were only a few independent craton formations scattered around the Earth. Around 1 Ga Columbia broke up to form Rodina - a series of continents attached to a central craton that formed the core of the North American Continent called Laurentia. In its turn Rodina broke up around 650 Ma, during a time called the Pan-African orogeny, and was reformed into a relatively short-lived supercontinent called Pannotia. This in turn broke apart around 560 Ma with the opening of the Iapetus Ocean to form the supercontinent Gondwana – coinciding, by good fortune, almost exactly with the Cambrian explosion and the appearance of life on land. In its turn Gondwana and other land masses eventually collected into one single landmass known as Pangaea around 300 million years ago, but then began to break apart about 175 million years ago into the forms of continents present today.  The name "Pangaea" is derived from Ancient Greek meaning ‘whole mother earth”.

6.32 The concept that the continents once formed a continuous land mass was first proposed by Alfred Wegener, the originator of the theory of continental drift, in his 1912 publication The Origin of Continents. The theory of continental drift was rejected by the scientific community for many years because there was a lack of a proven mechanism, and was only accepted in 1953. David Attenborough, who attended university in the second half of the 1940s, recounted an incident illustrating its lack of acceptance then: "I once asked one of my lecturers why he was not talking to us about continental drift and I was told, sneeringly, that if I could prove there was a force that could move continents, then he might think about it. The idea was moonshine, I was informed." Interestingly David Attenborough has made a BBC radio programme 60 years later, in 2016, about another theory that has been to date sneeringly rejected by many scientists – the Aquatic Ape theory. Attenborough’s productive scientific age would appear to be of such a length as itself requiring to be broken down into Eons, Era, Epochs and Periods.

6.33 The first evidence of advanced single-celled eukaryotes and multi-cellular life, Francevillian Group Fossils, roughly coincides with the start of the accumulation of free oxygen, ie around 2 billion years ago. It was also during the Proterozoic that the first symbiotic relationships involving mitochondria and cyanobacteria evolved.

6.34 The blossoming of eukaryotes such as acritarchs did not preclude the expansion of Cyanobacteria; in fact, stromatolites reached their greatest abundance and diversity during the Proterozoic, peaking roughly 1200 million years ago. Go Cyanobacteria!

6.35 Classically, the boundary between the Proterozoic and the Phanerozoic eons was set at the start of the Cambrian Period at 542 Ma when the first fossils of appeared. The Phanærozoic is the current geologic eon - the one during which visible animal and plant evolved. Its name was derived from ancient Greek for ‘visible life’, since it was once believed that all life began in this eon.

6.36 The first period of the Phanerozoic eon was marked by the “Cambrian explosion” - a gigantic leap forward in evolution of life on earth beginning exactly 542 million years ago, and ushering in the first of the three great geological era – imaginatively named the Paleozoic (from the Greek for ‘old life’) the Mesozoic (meaning middle life) and the Cenozoic (meaning, you guessed it, new life).

6.37 The Paleozoic lasted around 300 million years from 542 to 252 million years ago. It is the longest of the Phanerozoic eras, and is subdivided into six geologic periods (from oldest to youngest): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic era comprising all the above periods was a time of dramatic geological, climatic, and evolutionary change. Fish, arthropods, amphibians, anapsida, synapsida, euryapsida and diapsida all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, it was dominated by various forms of organisms. Great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, large, sophisticated diapsida and synapsida were dominant and the first modern plants (conifers) appeared. The Paleozoic Era ended with the largest mass extinction in Earth's history, the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the next Mesozoic Era to recover.

6.38 The Cambrian marked a profound change in life on Earth; prior to the Cambrian, the majority of living organisms on the whole were small, unicellular and simple; the Precambrian Charnia being exceptional. Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized—hence readily fossilized—organisms became common. Phylogenetic analysis has supported the view that during the Cambrian radiation, metazoa (animals) evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates.

6.39 Before the Cambrian, although diverse life forms prospered in the oceans, the land was comparatively barren—with nothing more complex than a microbial soil crust and a few molluscs that emerged to browse on the microbial biofilm. Most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia. The seas were relatively warm, and polar ice was absent for much of the period. All this was to change during the relatively short time of the Cambrian explosion as first plants, then insects, then animals colonised the land.

6.40 Next came the Ordovician era spanning 41 million up to the start of the Silurian Period in 444 Ma.

6.41 The following era was called the Silurian and spanned 24.6 million years up to the beginning of the Devonian Period in 419 Ma. As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The start of the Silurian is set, as is often the case between geological periods, at a major extinction event when 60% of marine species were wiped out. A significant evolutionary milestone during the Silurian was the diversification of jawed and bony fish. Multi-cellular life also began to appear on land in the form of small, bryophyte-like and vascular plants that grew beside lakes, streams, and coastlines, joining the terrestrial arthropods that are believed to have landed 500 million years ago during the Cambrian Period. However, terrestrial life would not greatly diversify and affect the landscape until the Devonian.

6.42 Which brings us to the next period, the Devonian which experienced the first significant adaptive radiation of life on dry land. Free-sporing vascular plants began to spread, forming extensive forests which covered the continents. By the middle of the Devonian, several groups of plants had evolved leaves and true roots, and by the end of the period the first seed-bearing plants appeared. Various terrestrial arthropods also became well-established. Fish reached substantial diversity during this time, leading the Devonian to often be dubbed the "Age of Fish". The first ray-finned and lobe-finned bony fish appeared, while the placoderms, armoured fish now extinct, began dominating almost every known aquatic environment.

6.43 The Carboniferous is the next geologic period that spans 60 million years up to the Permian around 300 Ma. Terrestrial life was well established by the Carboniferous period. Amphibians were the dominant land vertebrates, of which one branch would eventually evolve into reptiles, the first solely terrestrial vertebrates. Arthropods were also very common, and many were much larger than those of today. Vast swaths of forest covered the land, which would eventually be laid down and become the coal beds characteristic of the Carboniferous stratigraphy evident today. The atmospheric content of oxygen also reached their highest levels in geological history during the period, 35% compared with 21% today, allowing terrestrial invertebrates to evolve to great size. A major marine and terrestrial extinction event occurred in the middle of the period, caused by climate change. The later half of the period experienced glaciations, low sea level, and mountain building as the continents collided to form Pangaea.

6.44 The Permian witnessed the diversification of the early amniotes into the ancestral groups of the mammals, turtles, lepidosaurs and archosaurs. The world at the time was dominated by a single supercontinent known as Pangaea, surrounded by a global ocean called Panthalassa. The Carboniferous rainforest collapse of the previous period left behind vast regions of desert within the continental interior. Amniotes, who could better cope with these drier conditions, rose to dominance in place of their amphibian ancestors. The Permian ended with the largest mass extinction in Earth's history, in which nearly 90% of marine species and 70% of terrestrial species died out and it took 30 million years to recover.

6.45 The Mesozoic Era from about 252 to 66 million years ago is also called the Age of Reptiles, a phrase introduced by the 19th century paleontologist Gideon Mantell who viewed it as dominated by Diapsids such as Iguanodon, Megalosaurus, Plesiosaurus and Quetzalcoatlus. This Era is also the Age of Conifers. The era is subdivided into three major periods: the Triassic, Jurassic, and Cretaceous the first two of which have been made famous by movies, but the third “Cretaceous Park” still awaits its opportunity – which should be a big one given the period ended with the greatest extinction event ever known. The Mesozoic era began with the Permian–Triassic extinction event, and ended with the Cretaceous–Paleogene extinction event, another mass extinction which is known for having killed off non-avian dinosaurs, as well as other plant and animal species. The Mesozoic was a time of significant tectonic, climate and evolutionary activity. The era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses that would eventually move into their current positions. The climate of the Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was hotter than it is today. Non-avian dinosaurs appeared in the Late Triassic and became the dominant terrestrial vertebrates early in the Jurassic, occupying this position for about 135 million years until their demise at the end of the Cretaceous. Birds first appeared in the Jurassic, having evolved from a branch of theropod dinosaurs. The first mammals also appeared during the Mesozoic, but would remain small—less than 15 kg (33 lb)—until the Cenozoic.

6.46 The Triassic period which follows spans the next 52 million years up to the Jurassic in 201 Ma.   The first half was spent recovering from the previous extinction event. The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers (tri meaning "three") that are found throughout Germany and northwestern Europe—red beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstones—called the "Trias". Therapsids and archosaurs were the chief terrestrial vertebrates during this time. A specialized subgroup of archosaurs, called dinosaurs, first appeared in the Late Triassic but did not become dominant until the succeeding Jurassic Period. The first true mammals, themselves a specialized subgroup of Therapsids also evolved during this period, as well as the first flying vertebrates, the pterosaurs, who like the dinosaurs were a specialized subgroup of archosaurs. The vast supercontinent of Pangaea existed until the mid-Triassic, after which it began to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south. The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea's interior. However, the climate shifted and became more humid as Pangaea began to drift apart. The end of the period was marked by yet another major mass extinction, the Triassic-Jurassic extinction event, that wiped out many groups and allowing dinosaurs to assume dominance in the Jurassic.

6.47 The Jurassic period extends 56 million years up to 146 Ma and was named after the Jura Mountains within the European Alps, where limestone strata from the period were first identified. It was none other than Alexander von Humboldt who recognized the mainly limestone dominated mountain range of the Jura Mountains as a separate formation that had not been included in the established stratigraphic system defined by Abraham Gottlob Werner, and he named it "Jurakalk" in 1794.

6.48 By the beginning of the Jurassic, the supercontinent Pangaea had begun rifting into two landmasses, Laurasia to the north and Gondwana to the south. This created more coastlines and shifted the continental climate from dry to humid, and many of the arid deserts of the Triassic were replaced by lush rainforests. On land, the fauna transitioned to one dominated by dinosaurs alone. The first birds also appeared during the Jurassic, having evolved from a branch of theropod dinosaurs. Other major events include the appearance of the earliest lizards, and the evolution of therian mammals, including primitive placentals. Crocodilians made the transition from a terrestrial to an aquatic mode of life. The oceans were inhabited by marine reptiles such as ichthyosaurs and plesiosaurs, while pterosaurs were the dominant flying vertebrates

6.49 The long Cretaceous period followed for the next 79 million years. The Cretaceous period got its name from the type of rock deposited along the northern shores of the Tethys Sea in a band running from what is now Ireland and Britain to the Middle East. This rock formed from the deposits of the tiny limestone skeletons of diatoms is known as chalk. The Latin for chalk is creta, so the period was named the Cretaceous. In 1822, Jean-Baptiste-Julien Omalius d’Halloy used the name ‘Terrain Cretace’ to describe the chalk strata found in France. Since these same strata were also present across the English Channel, English geologists began calling using the same term. The Cretaceous was a period with a relatively warm climate, resulting in high sea levels and creating numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, and ammonites, while dinosaurs continued to dominate on land. At the same time, new groups of mammals and birds, as well as flowering plants, appeared. The Cretaceous ended with (yet another) large mass extinction, the Cretaceous–Paleogene extinction event, in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles, died out. The end of the Cretaceous is defined by the K–Pg boundary, a geologic signature associated with the mass extinction, which forms the boundary between the Mesozoic and Cenozoic eras.

6.50 In the Cretaceous oceans, rays, modern sharks and teleosts became common. Marine reptiles included ichthyosaurs in the early and mid-Cretaceous, plesiosaurs throughout the entire period, and mosasaurs appearing in the Late Cretaceous. The Hesperornithiformes were flightless, marine diving birds that swam like grebes. Globotruncanid Foraminifera and echinoderms such as sea urchins and starfish (sea stars) thrived. The first radiation of the diatoms (generally siliceous, rather than calcareous) in the oceans occurred during the Cretaceous; freshwater diatoms did not appear until the Miocene.

6.51 The Cenozoic Era covering the 66 million years until the present day, is also known as the Age of Mammals and the Age of Birds. Early in the Cenozoic the planet was dominated by relatively small fauna, including small mammals, birds, reptiles, and amphibians. From a geological perspective, it did not take long for mammals and birds to greatly diversify in the absence of the large reptiles that had dominated during the Mesozoic. Mammals came to occupy almost every available niche, both marine and terrestrial, and some also grew very large, attaining sizes not seen in most of today's terrestrial mammals.

6.52 The next period, the Paleogene, lasted 43 million years, a time when mammals evolved from relatively small, simple forms into a large group of diverse animals in the wake of the preceding extinction event. This period consists of the Paleocene, Eocene, and Oligocene Epochs.

6.53 The end of the Paleocene epoch in 55 Ma was marked by one of the most significant periods of global change during the Cenozoic, and led to the extinction of numerous deep-sea benthic foraminifera and on land, a major turnover in mammals.

6.54 The next epoch is the Eocene which lasts 20 million years up to the next major extinction event called the Grande Coupure (the "Great Break" in continuity) which may be related to the impact of one or more large meteorites exploding in the atmosphere in Siberia and in what is now Chesapeake Bay. The word Eocene from the Greek for ‘dawn + life’ refers to the dawn of the modern fauna that appeared during the epoch.

6.55 The last epoch of this period, the Oligocene, followed for the 10 million years up to 23 Ma. It was named after the Greek for ‘few + new’ because of the sparsity of extants forms of molluscs. (In a similar way the oligotrophic state of a lake is named from the Greek for ‘few + food’ ) The Oligocene is often considered an important time of transition, a link between the archaic world of the tropical Eocene and the more modern ecosystems of the Miocene. Major changes during the Oligocene included a global expansion of grasslands, and a regression of tropical broad leaf forests to the equatorial belt.

6.56 The Neogene is the most recent geological period covering the last 23 million years up to the present day.   During this period, mammals and birds continued to evolve into roughly modern forms, while other groups of life remained relatively unchanged. Early hominids, the ancestors of humans, appeared in Africa near the end of the period. Some continental movement took place, the most significant event being the connection of North and South America at the Isthmus of Panama, late in the Pliocene. This cut off the warm ocean currents from the Pacific to the Atlantic ocean, leaving only the Gulf Stream to transfer heat to the Arctic Ocean. The global climate cooled considerably over the course of the Neogene, culminating in a series of continental glaciations in the Quaternary Period that follows.

6.57 The Miocene is the epoch of the Neogene Period and extends from about up to around 5 Ma. It was named by Sir Charles Lyell after the Greek words ‘less + new” because it has 18% fewer modern sea invertebrates than the next epoch the Pliocene.

6.58 As the earth went from the Oligocene through the Miocene and into the Pliocene, the climate slowly cooled in a series of ice ages. Apes arose and diversified becoming widespread in the Old World. By the end of this epoch, around 6 Ma the ancestors of humans had split away from the ancestors of the chimpanzees to follow their own evolutionary path. As in the Oligocene before it, grasslands continued to expand and forests to dwindle in extent. In the Miocene seas, kelp forests made their first appearance and soon became one of Earth's most productive ecosystems. The plants and animals of the Miocene were fairly modern

6.59 The Pliocene Epoch continues up to around 2.6 Ma when major a glaciation heralded the start of the penultimate epoch, the Pleistocene, a time of ice ages which lasted until just 12,000 years ago - just a few thousand years after Lake Annecy had formed. Once again it was Charles Lyell who introduced this term when in 1839 as he described strata in Sicily that had at least 70% of their molluscan fauna still living today. This distinguished it from the older Pliocene Epoch, which Lyell had originally thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" from the Greek ‘most+new’ to contrast with the preceding preceding Pliocene (‘More New" ) and the immediately subsequent Holocene (‘wholly new’) epoch, which extends to the present time.

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