<P> Recent investigations about hunter - gatherer landscape burning has a major implication for the current debate about the timing of the Anthropocene and the role that humans may have played in the production of greenhouse gases prior to the Industrial Revolution . Studies on early hunter - gatherers raises questions about the current use of population size or density as a proxy for the amount of land clearance and anthropogenic burning that took place in pre-industrial times . Scientists have questioned the correlation between population size and early territorial alterations . Ruddiman and Ellis' research paper in 2009 makes the case that early farmers involved in systems of agriculture used more land per capita than growers later in the Holocene, who intensified their labor to produce more food per unit of area (thus, per laborer); arguing that agricultural involvement in rice production implemented thousands of years ago by relatively small populations have created significant environmental impacts through large - scale means of deforestation . </P> <P> While a number of human - derived factors are recognized as potentially contributing to rising atmospheric concentrations of CH (methane) and CO (carbon dioxide), deforestation and territorial clearance practices associated with agricultural development may be contributing most to these concentrations globally . Scientists that are employing a variance of archaeological and paleoecological data argue that the processes contributing to substantial human modification of the environment spanned many thousands of years ago on a global scale and thus, not originating as early as the Industrial Revolution . Gaining popularity on his uncommon hypothesis, palaeoclimatologist William Ruddiman in 2003, stipulated that in the early Holocene 11,000 years ago, atmospheric carbon dioxide and methane levels fluctuated in a pattern which was different from the Pleistocene epoch before it . He argued that the patterns of the significant decline of CO levels during the last ice age of the Pleistocene inversely correlates to the Holocene where there have been dramatic increases of CO around 8000 years ago and CH levels 3000 years after that . The correlation between the decrease of CO in the Pleistocene and the increase of it during the Holocene implies that the causation of this spark of greenhouse gases into the atmosphere was the growth of human agriculture during the Holocene such as the anthropogenic expansion of (human) land use and irrigation . </P> <P> Human arrival in the Caribbean around 6,000 years ago is correlated with the extinction of many species . Examples include many different genera of ground and arboreal sloths across all islands . These sloths were generally smaller than those found on the South American continent . Megalocnus were the largest genus at up to 90 kilograms (200 lb), Acratocnus were medium - sized relatives of modern two - toed sloths endemic to Cuba, Imagocnus also of Cuba, Neocnus and many others . </P> <P> Recent research, based on archaeological and paleontological digs on 70 different Pacific islands has shown that numerous species became extinct as people moved across the Pacific, starting 30,000 years ago in the Bismarck Archipelago and Solomon Islands . It is currently estimated that among the bird species of the Pacific, some 2000 species have gone extinct since the arrival of humans, representing a 20% drop in the biodiversity of birds worldwide . </P>

When did the last mass extinction occur apex