What is the difference between the formations of chalk versus chert? they are made of different source materials. they have different grain sizes. chalk is terrestrial; chert is marine. chalk is biochemical; chert is chemical?

The difference between formations of chalk versus chert is that they are made of different source materials.  Chalk is formed from lime mud, which accumulates on the sea floor which is then transformed into rock by geological processes while Chert forms when microcrystals of silicon dioxide grow within soft sediments that become limestone or chalk, chert formation can be either be of chemical or biological origin. 

Very minute and important evidence needs to be collected in order together detail and figure out what had happened

Lacking something of the ozone layer