Which of the following statements does not accurately describe precambrian earth? a. the atmosphere was similar to that of early mars and venus. b. the oceans were chemically different from modern oceans. c. the ocean water was salty and rich in dissolved oxygen. d. there were large amounts of water in earth’s mantle.

C. The ocean water was salty and rich in dissolved oxygen.  

Explanation:

The oldest and longest of the Geological Ages, the Pre-Cambrian extends from the formation of the Earth, approximately 4.5 billion years ago, to 570 million years ago.

This period begins with the formation of the Earth about 4.5 billion years ago, where the Earth was an incandescent mass with rivers of dissolved rock, erupting volcanoes and large amount of sulfur. The atmosphere was initially similar to the atmosphere of Mars and Venus and was composed of nitrogen, ammonia, hydrogen, carbon monoxide, methane and water vapor, expelled by volcanoes, and no sign of oxygen.

After 700 million years, most of the rocks on the surface of the earth had already been cooled and a large amount of water had condensed into an ocean. Even so, the volcanic eruptions were still constant and were giving rise to several islands that were pushed toward each other by the movement of the mantle. In this period small unicellular beings in the ocean begin to appear, the primitive algae and bacteria that assimilate the carbon dioxide of the atmosphere transforming it into free oxygen, slowly changing the composition of the atmosphere that, in that period, was composed basically by nitrogen and steam of Water. They are of this period the oldest fossils of the earth.

part 1: the half-life of the element is 22 years.

part 2: it will take 132.02 year for the sample to decay from 308.0 g to 4.8125 g.

explanation:

part 1: there are two ways to determine the half life time.

first way: the half life time can be determined directly from its definition as it is the time required for the sample to decay to its half concentration.

from the data the initial concentration was 45.0 g and decayed to its half value (22.5 g) in 22.0 years.

second way: the radio active decay is considered first order reaction so we can use the laws of first order reactions.

k = (1/t) ln (a/a-x), where k is the rate constant of the reaction,

t is the time of the reaction

a is the initial concentration of the reactant

a-x is the remaining concentration at time (t)

a = 45.0 g the initial concentration at t = 0 year.

at t = 22 year, a-x = 22.5 g

then k = (1/22 year) ln (45.0 g/ 22.5 g) = 0.0315 year-1.

the half-life time (t1/2) = ln 2/ k = 0.693/ k =0.693/ 0.0315 = 22 years.

part 2:

using the same law k = (1/t) ln (a/a-x),

using the given data; a = 308.0 g and a-x = 4.8125 g and the calculated k from the part 1 (k = 0.0315 year-1)

t = (1/k) ln (a/a-x) = (1/0.0315) ln (308.0/ 4.8125) = 132.02 years