Query: whenever in the past there was an explosion of plant life, the carbon dioxide content was far higher than at present.

Relevant passages:
Carbon dioxide <=SEP=> Carbon dioxide ( chemical formula ) is a colorless gas with a density about 60 % higher than that of air ( 1.225 g/L ) that is odorless at normally encountered concentrations . Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms . It occurs naturally in Earth 's atmosphere as a trace gas at a concentration of about 0.04 percent ( 400 ppm ) by volume . Natural sources include volcanoes , hot springs and geysers , and it is freed from carbonate rocks by dissolution in water and acids . Because carbon dioxide is soluble in water , it occurs naturally in groundwater , rivers and lakes , ice caps , glaciers and seawater . It is present in deposits of petroleum and natural gas .   As the source of available carbon in the carbon cycle , atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth 's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena . Plants , algae and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water , with oxygen produced as a waste product .   Carbon dioxide is produced by all aerobic organisms when they metabolize carbohydrates and lipids to produce energy by respiration . It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals , including humans . Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread , beer and winemaking . It is produced by combustion of wood and other organic materials and fossil fuels such as coal , peat , petroleum and natural gas .   It is a versatile industrial material , used , for example , as an inert gas in welding and fire extinguishers , as a pressurizing gas in air guns and oil recovery , as a chemical feedstock and in liquid form as a solvent in decaffeination of coffee and supercritical drying . It is added to drinking water and carbonated beverages including beer and sparkling wine to add effervescence . The frozen solid form of , known as `` dry ice '' is used as a refrigerant and as an abrasive in dry-ice blasting .   Carbon dioxide is the most significant long-lived greenhouse gas in Earth 's atmosphere . Since the Industrial Revolution anthropogenic emissions - primarily from use of fossil fuels and deforestation - have rapidly increased its concentration in the atmosphere , leading to global warming . Carbon dioxide also causes ocean acidification because it dissolves in water to form carbonic acid .

Botany <=SEP=> Botany , also called plant science ( s ) , plant biology or phytology , is the science of plant life and a branch of biology . A botanist or plant scientist is a scientist who specialises in this field . The term `` botany '' comes from the Ancient Greek word βοτάνη ( botanē ) meaning `` pasture '' , `` grass '' , or `` fodder '' ; βοτάνη is in turn derived from βόσκειν ( boskein ) , `` to feed '' or `` to graze '' . Traditionally , botany has also included the study of fungi and algae by mycologists and phycologists respectively , with the study of these three groups of organisms remaining within the sphere of interest of the International Botanical Congress . Nowadays , botanists ( in the strict sense ) study approximately 410,000 species of land plants of which some 391,000 species are vascular plants ( including ca 369,000 species of flowering plants ) , and ca 20,000 are bryophytes .   Botany originated in prehistory as herbalism with the efforts of early humans to identify -- and later cultivate -- edible , medicinal and poisonous plants , making it one of the oldest branches of science . Medieval physic gardens , often attached to monasteries , contained plants of medical importance . They were forerunners of the first botanical gardens attached to universities , founded from the 1540s onwards . One of the earliest was the Padua botanical garden . These gardens facilitated the academic study of plants . Efforts to catalogue and describe their collections were the beginnings of plant taxonomy , and led in 1753 to the binomial system of Carl Linnaeus that remains in use to this day .   In the 19th and 20th centuries , new techniques were developed for the study of plants , including methods of optical microscopy and live cell imaging , electron microscopy , analysis of chromosome number , plant chemistry and the structure and function of enzymes and other proteins . In the last two decades of the 20th century , botanists exploited the techniques of molecular genetic analysis , including genomics and proteomics and DNA sequences to classify plants more accurately .   Modern botany is a broad , multidisciplinary subject with inputs from most other areas of science and technology . Research topics include the study of plant structure , growth and differentiation , reproduction , biochemistry and primary metabolism , chemical products , development , diseases , evolutionary relationships , systematics , and plant taxonomy . Dominant themes in 21st century plant science are molecular genetics and epigenetics , which are the mechanisms and control of gene expression during differentiation of plant cells and tissues . Botanical research has diverse applications in providing staple foods , materials such as timber , oil , rubber , fibre and drugs , in modern horticulture , agriculture and forestry , plant propagation , breeding and genetic modification , in the synthesis of chemicals and raw materials for construction and energy production , in environmental management , and the maintenance of biodiversity .

Eocene <=SEP=> The Eocene ( -LSB- pronˈiːəˌsiːn , _ ˈiːoʊ - -RSB- ) Epoch , lasting from , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era . The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch . The start of the Eocene is marked by a brief period in which the concentration of the carbon isotope 13C in the atmosphere was exceptionally low in comparison with the more common isotope 12C . The end is set at a major extinction event called the Grande Coupure ( the `` Great Break '' in continuity ) or the Eocene -- Oligocene extinction event , which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay . As with other geologic periods , the strata that define the start and end of the epoch are well identified , though their exact dates are slightly uncertain .   The name Eocene comes from the Ancient Greek ἠώς ( ēṓs , `` dawn '' ) and καινός ( kainós , `` new '' ) and refers to the `` dawn '' of modern ( ` new ' ) fauna that appeared during the epoch .