We humans have brought ourselves to a fascinating and challenging point. By our numbers and our choices, particularly in the last 200 years, we’ve grown into an equivalent of the geological forces that have shaped our planet over its 4.5 billion year life. Our effect on the thin layer of atmosphere blanketing the earth means that we are potentially altering the ability of every living thing to prosper, or even exist. Our use of resources — forests, water, air, minerals, soil — is far outstripping the earth’s ability to replenish them. Millions of people worldwide are grappling with these challenges, which represent not just things to do but require new ways to think.