Third, there was the problem of why some parts of the Earth's surface (crust) should have solidified while other parts were still fluid.
तीसरे, एक समस्या यह थी कि पृथ्वी की सतह (क्रस्ट) का कुछ भाग ठोस है तथा अन्य भाग द्रव क्यों है।