Here is one of the ways humanity can act as Earth’s defense system.
What other roles do – or can – we play as an intrinsic and temporary part of this living planet?
We are its eyes, ears, senses, along with many other critters.
We are one way for the Earth to reflect and explore itself in thoughts.
We are one way for the Earth to feel itself.
We are one way for the Earth to imagine.
We enhance its senses through out technology, through telescopes, microscopes, scanners and much more.
We are its tentacles and emissaries through space exploration.
We are the Earth watching itself, in awe, as one whole system through astronauts and cosmonauts, and through all of us watching video and images of the Earth from space.
We are the Earth in awe of itself and the universe.
We are the Earth developing and exploring itself through culture – a creative diversity of cultures.
We are the Earth being creative in new and different ways, not only through biology but now also through culture and technology.
We are the Earth looking for other living planets through SETI.
We are, perhaps, the Earth’s reproductive system, through future terraforming.
We have all of these and many more functions for the Earth, and so also for the universe. As Carl Sagan said, we are one way of the universe to know itself. We are it’s local eyes, ears, thoughts and feelings.
And just to mention it: Defending the Earth against impact is very helpful for humanity, but the Earth doesn’t really need it. Such impacts, and other major disasters in past, have proved quite fruitful for this living planet. We wouldn’t have been here without it. The universe and the Earth is not only a continuous process of creativity, but death is essential for this creativity. The death of stars produce matter. The death of species allow room for new species. The death of individuals allow room for new individuals. Death is essential for life at all levels. (See Connie Barlow and Michael Dowd’s page on death as natural, creative and generative.)