Prime Minster Narendra Modi on Saturday said that Earth Day is an occasion to reiterate a firm resolve to keep the planet clean and green."Earth Day is a day of gratitude to mother earth," Modi said."It is our duty to live in harmony with the plants, animals and birds we share the earth with. We owe this to our future generations."He hoped that this year's theme of 'Environmental and Climate Literacy' helps in creating awareness on protecting nature and natural resources.According to the Earth Day Network, April 22 marks the anniversary of the birth of the modern environmental movement in 1970.