(I am taking a risk in making a fool of myself in front of all you Chinese Scholars, but I am going to put in my two bits.) Lao Tzu said " 天地不仁". I interprete it as "Nature is indifferent" . I.e. nature takes no sides . "Nature" is an emotionless entity. However, if nature is sentient, it will get entangled with emotional judgements and frustration and will be worn down by such emotions and grows old like all mortal sentients.
So I would venture to translate the first phrase as:
"If nature is sentient, it would not be ageless."
and the second phrase as "Just as it is normal to see earth changes into seas".
从毛泽东的哲学思想来看，“沧桑”应该是指“变”， 这是有迹可寻的。所谓“任何事物都是变化发展的， 变是绝对的，不变是相对的”即是。故革命是他一生 最为热衷的事业，革命就是“变”。由此看来“正道” 并不一定是指“正义”， 而是指客观的自然规律， law of nature,毛泽东这里想说的是：变是客观规律， 是不以人的意志为转移的。
再看其他几个用法，无论是“自然神论者”还是“无神论者”，把各 自的信仰读入中国文化传统中的“天”，都有待商榷。“Heaven”虽 说也有问题，但是它毕竟是个富有诗意的宗教概念，不是科学概念。 在西方，“Heaven”往往也是一种神圣的名称，常与“God”互换使 用，如“天国”既可用“Kingdom of God”也可用“Kingdom of Heaven”。但是，具体到这句诗，用“God”就有点将中国“基督化 ”的味道，太唐突，不如“Heaven”那样相对中性一点。
The gender distinction could be due to the fact that Mars is named after the god of war, a masculine figure while Venus is named after the goddess in the half-shell (ha Ha!)
There is also a popular saying that: Men are from Mars and women are from Venus.