Which word in the passage means “caring and protecting?”

Directions: Read the passage and answer the question that follows.
     
Scientists believe that life on Earth began in the ocean, approximately 4 billion years ago. And in fact, it was only about 500 million years ago that life emerged from the ocean onto the land. That means that ocean life has existed for 8 times longer period. So, no matter how unimaginably long it was since the first creatures crawled out on land, to the age of the dinosaurs and to our time, all of that is but a small slice of a pie compared to the vast span of time in which the oceans have nurtured life. And even today, although living things now exist on nearly every part of the Earth's surface, in so many different forms, the ocean continues to be critically important to life on Earth.
To begin with, the ocean covers 70% of the Earth's surface and is still the home of the majority of Earth's living creatures. Secondly, the oceans are a vital part of the water cycle that brings rain to our crops and forests -- and drinking water to our cities. And the ocean also produces much of the oxygen upon which all human beings and animals depend. Many of our recent medical and scientific breakthroughs have been made possible in one way or another through ocean based research. Finally, the oceans provide fish and shellfish and other vital resources upon which humans depend, including jobs for millions of people.