Chalk forms from ________.
A)the hard parts of microscopic organisms that accumulate on the sea floor
B)magnesium rich fluids that chemically alter limestone bearing reefs
C)direct precipitation from seawater
D)evaporation of magnesium rich waters

Question

Quizplus · Accepted Answer

Chalk is primarily made up of the hard parts of microscopic organisms, such as coccolithophores and foraminifera, that accumulate on the sea floor over time. These organisms have hard shells made of calcium carbonate (the same mineral that makes up limestone) and when they die, their shells sink to the sea floor and accumulate in large quantities, forming chalk. While magnesium-rich fluids and direct precipitation from seawater can play a role in chalk formation, it is primarily a result of the accumulation of these microscopic organisms. Evaporation of magnesium-rich waters is not a significant factor in the formation of chalk.

Chalk Forms from ________