The Gran Chaco (Quechua chaku, "hunting land") is a sparsely populated, hot and semi-arid lowland natural region of the Río de la Plata basin, divided among eastern Bolivia, Paraguay, northern Argentina and a portion of the Brazilian states of Mato Grosso and Mato Grosso do Sul, where it is connected with the Pantanal region. This land is sometimes called the Chaco Plain.

The Gran Chaco is about 647,500 km² (250,001 sq mi) in size, though estimates differ. It is located west of the Paraguay River and east of the Andes, mostly an alluvial sedimentary plain shared among Paraguay, Bolivia and Argentina. It stretches from about 17° to 33° South latitude and between 65° and 60° West longitude, though estimates differ in this case too.

Historically the Chaco has been divided in three main parts: the Chaco Austral or Southern Chaco, south of the Bermejo River and inside Argentinian territory, blending into the Pampa region in its southernmost end; the Chaco Central or Central Chaco between the Bermejo and the Pilcomayo River to the north, also now in Argentinian territory; and the Chaco Boreal or Northern Chaco, north of the Pilcomayo up to the Brazilian Pantanal, inside Paraguayan territory and sharing some area with Bolivia.

Maria Osmarina Marina Silva Vaz de Lima (born near Rio Branco, in Acre on February 8, 1958) is a Brazilian environmentalist and politician. Ms. Silva was a colleague of Chico Mendes, who was assassinated for defending the Amazon environment. She was a member of the Partido dos Trabalhadores until August 19, 2009 and served as a senator before becoming environmental minister in 2003. In 1996, Ms. Silva won the Goldman Environmental Prize for South & Central America. In 2007, the United Nations Environment Program named her one of the Champions of the Earth and the 2009 Sophie Prize. Running in the 2010 Brazilian elections, she won 19.4% of the popular votes.

In 2010, she along with Cécile Duflot, Monica Frassoni, Elizabeth May and Renate Künast were named by Foreign Policy magazine to its list of top global thinkers, for taking Green mainstream.

Ms. Silva is descendent of Portuguese and black African parents on both her maternal and paternal lines. Silva grew up as one of eleven children in a community of rubber tappers on the Bagasse (Bagaço) rubber tree plantation (Portuguese Seringal Bagaço), in the western state of Acre. Orphaned at age 16, young Marina moved to the state capital, Rio Branco, where she received a Catholic education as she worked as a maid. She graduated in history from the Federal University of Acre at 26 and became increasingly politically active. In 1984 Ms. Silva helped create Acre's first workers' union. She led demonstrations called empates with Chico Mendes to warn against deforestation and the outplacement of forest communities from their traditional locations.