The following graph shows the average pH of the ocean over the last 20 million years of Earth's history.8.48.38.2-금 8.1 -8.07.9-15-10Time (millions of years before the present)Source: Acidification Model Source CO2SYS (Pierrot, Lewis and Wallace. 2006. Carbon Dioxide Information Analysis Center, ORNL, US DOE, Oak Ridge, TN, USA)What can be concluded from the graph? Select all that apply.-25-2005Ocean acidity has been steadily increasing from 20 million years ago to the present time.Average ocean pH has fluctuated over the millennia from just over 8.0 to about 8.3.In the last 20 million years of Earth's history, the average pH has never gone below 8.0.Ocean acidity has been steadily decreasing from 20 million years ago to the present time.

pH is a measure of the acidity, or alkalinity, of a solution. The pH ranges from zero to 14. A pH of 7.0 is considered neutral. The values below 7.0 are acidic, and those above 7.0 are basic or alkaline. An alkaline pH is more conducive to human life. The pH of blood is maintained over a narrow range and is slightly basic. Similarly, the pH of the ocean is also alkaline. Factors such as the minerals washed into the ocean by groundwater and the percentage of carbon dioxide and oxygen dissolved in ocean water affect its pH.Though the pH of the ocean varies from place to place, it always remains in the basic range. The most acidic ocean on earth has a pH of 7.7. The variety of life thriving in the ocean depends on maintaining this pH balance.The graph shows the average pH values of the ocean over millions of years. The given statements in the options are evaluated below for their deduction from the graph:Ocean acidity has been steadily increasing from 20 million years ago to the present time.This statement is incorrect.The graph shows that the pH has fluctuated over a small range, in that it has increased at times and also decreased at times. Over certain long periods, the average pH has been steadily maintained. Therefore, the pH has not been steadily increasing.Average ocean pH has fluctuated over the millennia from just over 8.0 to about 8.3This statement is correct.The graph shows that the pH hit its peak around 15 million years ago, when it reached 8.3. At all other times, it has remained just above 8.0 and fluctuated between these two values.In the last 20 million years of the earth's history, the average pH has never gone below 8.0.This statement is correct.The graph does not show pH falling below 8.0 at any given point in the earth's history. It has always remained just above 8.0 throughout.Ocean acidity has been steadily decreasing from 20 million years ago to the present time.This statement is incorrect.The graph shows that the pH has fluctuated over a small range, in that it has increased at times and also decreased sometimes. Over certain long periods, the average pH has been steadily maintained. Therefore, the pH has not been steadily decreasing.Therefore, the two correct statements are:Average ocean pH has fluctuated over the millennia from just over 8.0 to about 8.3In the last 20 million years of the earth's history, the average pH has never gone below 8.0These two statements are very well supported by the graph.