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.
True. It's to my knowledge that gas has no smell, so they add this stinky stuff so it can be detected.
Answer:C( A green color
Explanation:Brownian motion. This is the motion of small objects (like pollen) that appear to jiggle around while sitting in a drop of water. You can view this motion under a microscope.
Explanation:
The core threats to biodiversity are human population growth and unsustainable resource use. To date, the most significant causes of extinctions are habitat loss, introduction of exotic species, and overharvesting.
Answer:
C. a whale's flipper and a cat's leg
Explanation:
Homologous structures are the organs which have same basic anatomical structure but they perform different function based on the type of environment in which the organism is living. Two organisms which have homologous organs indicate that both the organisms are evolutionarily closely related to each other i.e. their ancestry is common. It is basically divergent evolution which is responsible for formation of homologous organs. If two closely related organisms are living in different environment then their organs which basically have same origin will tend to perform different functions as a part of adaptation. In contrast to this, analogous structures are the ones which perform similar function but anatomically they are very different and evolutionarily they are not closely related. Analogous structures are evolved as a result of convergent evolution which is meant for adaptation in a particular environment. So, even if two organisms are not closely related they still develop the structures which perform similar function so as to adapt into a particular environment.
Whales and cats both are mammals so they are closely related to each other but since they live in different environment, their organs which are anatomically similar perform different functions. Flippers in whales help in swimming while cat's leg help in walking. So, option C is correct answer.
All other options are examples of analogous organs.
A bird's wings and a butterfly's wings are perfect example of analogous organs. A bird is a vertebrate while a butterfly is an arthropod so evolutionarily they are very distantly related so their wings are also anatomically very dissimilar but they still perform similar function which help these two organisms in flying. So option A is incorrect. Similarly option D is also incorrect because wasp is an arthropod while dolphin is a vertebrate. Option B is also incorrect because catfish is a vertebrate and bee is an arthropod.
