Why are fossils of early life on Earth rarer than fossils of plants and animals from the past few hundred million years?
A) We find fossils in sedimentary layers, and no sediments were deposited until just a few hundred million years ago.
B) Life was far less abundant prior to a few hundred million years ago.
C) Early organisms were microscopic and lacked skeletons and other hard structures that are most likely to be fossilized.
D) Fossils could not form before there was oxygen in the atmosphere.
C
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Hydrogen gas seems to have a diffusivity of about 2.6 x 10^-13 m^2/s when diffusing into iron at 770 K. What would you expect the rate of diffusion or mass flow rate per unit area of hydrogen to be when stored in an iron container at 5 atmospheres pressure, assuming the density of hydrogen at 1 mm in the iron from the containing surface to be 5% of the normal hydrogen density, given by p/RT?
What will be an ideal response?
State the condition of stable equilibrium
What will be an ideal response?
Which statements are true about a VIRTUAL image? (There may be more than one correct choice.)
A) Its location can be calculated, but it cannot be viewed directly by your eye without using auxiliary lenses. B) It cannot be photographed. C) It cannot be viewed on a screen. D) A plane mirror always forms a virtual image. E) A concave lens always forms a virtual image.
A sample of U235 that is below the critical mass will not sustain a chain reaction because
A. too many neutrons escape through the surface of the sample without initiating fission. B. the heat produced by the spontaneous fission of some nuclei is insufficient. C. the inertia of the sample is too low for efficient fission. D. nuclei repel each other due to their positive charges.