高機率機經閱讀：Where does life come from? 生命起源

 (重點用藍色字體標示，並附上重點單字，同學要特別注意喔！)

生命起源的三個理論：

理論一 Significance of Water

Everyone knows that liquid water is essential for humans to survive. In fact, it is essential in the chemistry of all biological systems. Water provides the medium in which the transport of molecules can occur in reactions. Because water is necessary for all life, scientists look for evidence of liquid water wherever they search for life, whether it is somewhere on Earth, or even somewhere else in our solar system or beyond.

理論二：來自外太空的有機物體

An alternative to Earthly abiogenesis is the hypothesis that primitive life may have originally formed extraterrestrially, either in space or on a nearby planet

外太空富含有機物，特別是太陽系以外，由於離太陽遠，受熱少，氣體不容易揮發。

彗星外有一層像柏油的物質包圍，包含著複雜的有機物質，可能藉由撞擊到地球表面而留下這些有機分子。
Organic compounds are relatively common in space, especially in the outer solar system where volatiles (易揮發氣體) are not evaporated by solar heating. Comets are encrusted (被一層…包圍)by outer layers of dark material, thought to be a tar-like (柏油) substance composed of complex organic material formed from simple carbon compounds after reactions initiated mostly by irradiation ( 輻射) by ultraviolet light. It is supposed that a rain of material from comets could have brought significant quantities of such complex organic molecules to Earth.

理論三：深海溝 （hydrothermal vent)

在深海溝的化學物質有足夠能量產生生命的許多化學反應，

DNA也顯示眾多生命都起源於高溫下的海洋微生物。（aquatic microorganism)

Scientists are exploring several possible locations for the origin of life, including tide pools and hot springs. However, recently some scientists have narrowed in on the hypothesis that life originated near a deep sea hydrothermal vent. The chemicals found in these vents and the energy they provide could have fueled many of the chemical reactions necessary for the evolution of life. Furthermore, using the DNA sequences of modern organisms, biologists have tentatively traced the most recent common ancestor of all life to an aquatic microorganism that lived in extremely high temperatures — a likely candidate for a hydrothermal vent inhabitant! Although several lines of evidence are consistent with the hypothesis that life began near deep sea vents, it is far from certain: the investigation continues and may eventually point towards a different site for the origin of life.

Supporters of this theory claim that the organic molecules at the thermal vents are not formed in 300^oC temperatures, but rather in a gradient(坡度，這裡指溫度漸漸下降的地方) formed between the hydrothermal vent water, and the extremely cold water, 4^oC (39.2^oF), which surrounds the vent at the bottom of the ocean.

The temperatures at this gradient would be suitable for organic chemistry to occur.