A. Earth's magnetic field reverses over time; the changes show that seafloor spreading has taken place over time.
Explanation:
The pattern of the magnetic minerals in seafloor ridges are aligned in a repeating pattern because the earth's magnetic field reverses overtime.
This provides evidence because the changes shows that the sea floor spreading has taken place over time.
- The concept of sea floor spreading was first suggested by Harry Hess in the early 1960's.
- Using sophisticated tools, he was able to discover stripe patterns of magnetic minerals in rocks.
- The earth can be likened to a giant bar magnet
- The geomagnetic field originates from the core where the movement of molten metals induces magnetism.
- In a fresh cooling magma, the metallic minerals are able to align their domains with the prevailing magnetic field.
- At some point the magnetic field is normal with a very strong intensity. At other times the intensity is low and it reverses.
- The minerals keeps track of the changes.
- This leads to striped pattern that has been used to suggest sea floor spreading.
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In geology, a graded bed is one characterized by a systematic change in grain or clast size from one side of the bed to the other. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer onesI just learned about this in our rocks and minerals unit for science,
The correct answer is option (d) They allow the exchange of gases between cells in the leaf and the external environment.
Stomata are the tiny openings present in the epidermis (outer layer of cells) of the leaf. They have a pore which is guarded by the guard cells which controls the opening and closing of the stomata. Air enters and exits through the stomata.
The main funtion of stomata is to facilitate the gaseous exchange. The gas exchange that occurs when the stomata are open helps in the process of photosynthesis. During photosynthesis, carbon dioxide is taken in from the atmosphere and oxygen is released as a by-product of photosynthesis. The glucose produced is converted into the starch and stored in the leaves.
Also, water vapour diffuses through the stomata into the atmosphere by a process called the transpiration.
Thus, stomata are the structures that are mainly involved in the gaseous exchange between the cells of the leaf and the atmosphere.
