Query: "The killer proof that CO2 does not drive climate is to be found during the Ordovician- Silurian and the Jurassic-Cretaceous periods when CO2 levels were greater than 4000 ppmv (parts per million by volume) and about 2000 ppmv respectively.

Relevant passages:
Devonian <=SEP=> The Devonian is a geologic period and system of the Paleozoic , spanning 60 million years from the end of the Silurian , million years ago ( Mya ) , to the beginning of the Carboniferous , Mya . It is named after Devon , England , where rocks from this period were first studied .  The first significant adaptive radiation of life on dry land occurred during the Devonian . Free-sporing vascular plants began to spread across dry land , 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 placodermi began dominating almost every known aquatic environment .   The ancestors of all four-limbed vertebrates ( tetrapods ) began adapting to walking on land , as their strong pectoral and pelvic fins gradually evolved into legs . In the oceans , primitive sharks became more numerous than in the Silurian and Late Ordovician . The first ammonites , species of molluscs , appeared . Trilobites , the mollusk-like brachiopods and the great coral reefs , were still common . The Late Devonian extinction which started about 375 million years ago severely affected marine life , killing off all placodermi , and all trilobites , save for a few species of the order Proetida .   The palaeogeography was dominated by the supercontinent of Gondwana to the south , the continent of Siberia to the north , and the early formation of the small continent of Euramerica in between .

Triassic <=SEP=> The Triassic ( -LSB- prontraɪˈæsɪk -RSB- ) is a geologic period and system which spans 50.9 million years from the end of the Permian Period million years ago ( Mya ) , to the beginning of the Jurassic Period Mya . The Triassic is the first period of the Mesozoic Era . Both the start and end of the period are marked by major extinction events .   The Triassic began in the wake of the Permian -- Triassic extinction event , which left the earth 's biosphere impoverished ; it would take well into the middle of this period for life to recover its former diversity . 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 allowed dinosaurs to assume dominance in the Jurassic .   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 '' .

Silurian <=SEP=> The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period , at million years ago ( Mya ) , to the beginning of the Devonian Period , Mya . 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 base of the Silurian is set at a major Ordovician-Silurian 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 , and terrestrial arthropods are also first found on land during the Silurian . However , terrestrial life would not greatly diversify and affect the landscape until the Devonian .

Jurassic <=SEP=> The Jurassic ( -LSB- prondʒuːˈræsɪk -RSB- from Jura Mountains ) is a geologic period and system that spans 56.3 million years from the end of the Triassic Period million years ago ( Mya ) to the beginning of the Cretaceous Period Mya . The Jurassic constitutes the middle period of the Mesozoic Era , also known as the Age of Reptiles . The start of the period is marked by the major Triassic -- Jurassic extinction event . Two other extinction events occurred during the period : the Pliensbachian/Toarcian event in the Early Jurassic , and the Tithonian event at the end ; however , neither event ranks among the `` Big Five '' mass extinctions .   The Jurassic is named after the Jura Mountains within the European Alps , where limestone strata from the period were first identified .  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 from the Triassic fauna , dominated by both dinosauromorph and crocodylomorph archosaurs , 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 .

Ordovician <=SEP=> The Ordovician ( -LSB- pronɔrdəˈvɪʃən -RSB- ) is a geologic period and system , the second of six periods of the Paleozoic Era . The Ordovician spans 41.2 million years from the end of the Cambrian Period million years ago ( Mya ) to the start of the Silurian Period Mya . The Ordovician , named after the Celtic tribe of the Ordovices , was defined by Charles Lapworth in 1879 to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison , who were placing the same rock beds in northern Wales into the Cambrian and Silurian periods , respectively . Lapworth recognized that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods , and placed them in a period of their own . It received international sanction in 1960 , when it was adopted as an official period of the Paleozoic Era by the International Geological Congress .   Life continued to flourish during the Ordovician as it did in the earlier Cambrian period , although the end of the period was marked by the Ordovician -- Silurian extinction event . Invertebrates , namely molluscs and arthropods , dominated the oceans . The Great Ordovician Biodiversification Event considerably increased the diversity of life . Fish , the world 's first true vertebrates , continued to evolve , and those with jaws may have first appeared late in the period . Life had yet to diversify on land . About 100 times as many meteorites struck the Earth during the Ordovician compared with today .