When did the ozone layer become thick enough to provide an effective UV screen?
What will be an ideal response?
The O3 layer should have been absorbing most UV radiation by 2.3 Ga, as soon as O2 levels began to rise. An O2 level of 1% PAL is sufficient to create an efficient ozone screen.
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As of 2013, nearly 700 university presidents had signed a University Presidents' Commitment to ________
A) conserve water B) reduce solid wastes C) take inventories and set dates for becoming carbon-neutral D) increase campus biodiversity E) increase electrical consumption
What is luster?
a. a mineral's ability to transmit light through itself b. the color of a mineral in powdered form c. an indication that a mineral has double refraction d. the quality of light reflected from a mineral's surface e. the color of a mineral
Which of the following is true about Japan and colonization in the 19th century?
A) Meiji clan sought to westernize culture B) Japan was open to foreigners in the 1870s C) Japan's military moved into Russia D) Japan's military moved into China E) all of the above
What kind of seawater is densest?
A) cold, low salinity B) warm, low salinity C) warm, high salinity D) cold, high salinity