아래 글에서 the hard layer 가 무엇을 지칭하는지 모르겠습니다. 그리고 표시된 문장 해석이 논리적으로 이해가 안됩니다. "위의 층의 무게에 눌려 소금성분이 위로 올라왔다?"
이거 명쾌하게 알려주실분 없나요?
3 With questions such as these clearly before them, the scientists aboard the Glomar
Challenger proceeded to the Mediterranean to search for the answers. On August 23,
1970, they recovered a sample. The sample consisted of pebbles of hardened
sediment that had once been soft, deep-sea mud, as well as granules of gypsum1
and fragments of volcanic rock. NIn the days following,
samples of solid gypsum were repeatedly brought on deck as drilling operations
penetrated the seafloor. Furthermore, the gypsum was found to possess peculiarities
of composition and structure that suggested it had formed on desert flats. Sediment
above and below the gypsum1 layer contained tiny marine fossils, indicating openocean
conditions. As they drilled into the central and deepest part of the Mediterranean
basin, the scientists took solid, shiny, crystalline salt from the core barrel. Interbedded
with the salt were thin layers of what appeared to be windblown silt.
4 The time had come to formulate a hypothesis. The investigators theorized that about
20 million years ago, the Mediterranean was a broad seaway linked to the Atlantic
by two narrow straits. Crustal movements closed the straits, and the landlocked
Mediterranean began to evaporate. Increasing salinity caused by the evaporation
resulted in the extermination of scores of invertebrate species. Only a few organisms
especially tolerant of very salty conditions remained. As evaporation continued, the
remaining brine (salt water) became so dense that the calcium sulfate of the hard
layer was precipitated. In the central deeper part of the basin, the last of the brine
evaporated to precipitate more soluble sodium chloride (salt). Later, under the weight
of overlying sediments, this salt flowed plastically upward to form salt domes. Before
this happened, however, the Mediterranean was a vast desert 3,000 meters deep.
Then, about 5.5 million years ago came the deluge. As a result of crustal adjustments
waters tore into the hardened salt flats, broke them up, and ground them
into the pebbles observed in the first sample taken by the Challenger. As the basin
was refilled, normal marine organisms returned. Soon layers of oceanic ooze began to
accumulate above the old hard layer.