The correct answer is an accumulation of microorganisms in deep marine environments.
Chalk rock refers to a pure form of limestone produced in tropical and warm seas about 100 million years ago in the Cretaceous period. The microscopic marine algae known as coccoliths thrived in the ancient seas. Their shells were comprised of calcite. With the death of the algae, their bodies sunk to the floor of the sea and sediment of chalk got deposited.
Over many years layers of chalk sediment got deposited and resulted in compaction of loose sediment into solid chalk rock.
Answer: Option A
Explanation:
Scientist used the domain Eukarya which comprises the togetherness of all the eukaryotic species. They have been put together because all of the eukaryotic species have their recent common ancestor as eukaryotes.
The first eukaryotic cells, which had nucleus originated 2 billion years ago which had organelles. They explain the endosymbiotic theory.Most of the eukaryotic species that have been evolved from this.
Eukaryotic species have been evolved from another eukaryotic species and share some similar characteristics.
The answer is B. Cnidarians
Cnidarian body has no left or right side, only tom and bottom surfaces. If you divide cnidarian a about central point, you will get equal parts. So, cnidarians are radially symmetrical animals. This group includes hydroids, jellyfish, anemones, and corals. In all groups, animals have stinging cells on tips of tentacles. They use them to capture the prey. Their name literally means stinging creatures.
In geology, a key bed (syn marker bed) is a relatively thin layer of sedimentary
rock that is readily recognized on the basis of either its distinct
physical characteristics or fossil content and can be mapped over a very
large geographic area.[1]
As a result, a key bed is useful for correlating sequences of
sedimentary rocks over a large area. Typically, key beds were created as
the result of either instantaneous events or (geologically speaking)
very short episodes of the widespread deposition of a specific types of sediment. As the result, key beds often can be used for both mapping and correlating sedimentary rocks and dating them. Volcanic ash beds ( and bentonite beds) and impact spherule beds, and specific megaturbidites
are types of key beds created by instantaneous events. The widespread
accumulation of distinctive sediments over a geologically short period
of time have created key beds in the form of peat beds, coal beds, shell beds, marine bands, black in cyclothems, and oil shales. A well-known example of a key bed is the global layer of iridium-rich impact ejecta that marks the Cretaceous–Paleogene boundary (K–T boundary). Please let me know if it works.
