D) The Earth was hit by a one or more objects from space 65 million years ago. The iridium layer shows an extraterrestrial cause for the extinction at the Cretaceous Tertiary boundary, discovered by the Alvarez family. The first discovery of this layer was in the Bavarian alps, in Lattengebirge. The Alverez family proposed that the extinction of the dinosaurs was due to a large meteor hitting the Earth at the end of the Cretaceous period, marking the KT boundary with this clay layer which has a high content of iridium. Iridium is not common on Earth, but is common in meteors.
Answer:
B. Populations of amphibians in a few local areas have declined dramatically in the last few decades
Explanation:
The continuous, low-level extinction of species that has occurred throughout the World and at least six species of frogs have not been seen for one to three decades and also it has recently been discovered that some species of salamander-specific chytrid has gone into extinction
Answer:
Because natural selection selects for it. Thus it persists.
Explanation:
You have to understand heterozygote advantage. Basically, it's where heterozygotes have an advantage over homozygotes. In the case of sickle cell disease, heterozygotes have an advantage, and natural selection favors whatever is advantageous. Thus, because heterozygotes each have one recessive sickle-cell allele, as natural selection favors the heterozygotes, the recessive sickle-cell allele persists and remains in the gene pool.
The dominant and recessive pair, A
Answer:
negative feedback loop involving insulin and glucagon help to keep blood glucose levels within a narrow concentration range. If glucose levels get too high, the body releases insulin into the bloodstream.
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