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The International Encyclopedia of Human Geography is a 2009 academic reference work covering human geography. The editors-in-chief are Rob Kitchin and Nigel Thrift and it contains a foreword by Mary Robinson .
Later, around 1.7 billion years ago, multicellular organisms began to appear, with differentiated cells performing specialised functions. [ 111 ] Algae-like multicellular land plants are dated back to about 1 billion years ago, [ 112 ] although evidence suggests that microorganisms formed the earliest terrestrial ecosystems , at least 2.7 ...