Many Nature Religions, Old Religions, Pagan Religions have the belief that Earth is the 'mother' who mated with a father (a god) and life came forth from that union. Some Native American Traditions have the sky as 'Father Sky' and the Earth as 'Mother Earth' as an example of this. Earth is a 'female' name, as well is Terra and the other names we have applied to Earth. Most of the Nature Religions wondered 'where did we come from' and looking about them at the abundance of life they made the assumption that life sprung up out of the earth and that Earth 'gave birth' to life. This is somewhat backed up by the idea that life spontaneously emerges. For instance a rotting corpse will appear to spontaneously produce maggots. But then fly eggs are most difficult to see with the naked eye, thus a bit of meat that was left for the flies to land and lay eggs appeared to have nothing to 'mate with' to bear life (maggots). There are other examples of life 'suddenly' appearing, ponds and lakes around the world that go dry during the summer will fill up during the winter rains, life will emerge from the mud to re-spawn in the lake. Folk mostly didn't know that eggs and 'seeds of life' were waiting for rain - thus it looks like the earth just produces life on its own. With such observations religions built up around them, thus we are blessed with the concept that Earth is the mother of life. In a round about way while science has demonstrated that life doesn't just 'appear' in the places it seems like, the process of evolution appears to uphold the concept of life generating out of 'nothing'. It theorizes and we have demonstrated in labs that simple organic compounds (life) can be generated by the raw materials that earth has. Thus Earth gave birth to life.

"Mother Nature (sometimes known as Mother Earth) is a common representation of nature that focuses on the life-giving and nurturing features of nature by embodying it in the form of the mother. Images of women representing mother earth, and mother nature, are timeless. In prehistoric times, goddesses were worshipped for their association with fertility, fecundity, and agricultural bounty." Source and further information: http://en.wikipedia.org/wiki/Mother_Nature