There are all sorts of ways to reconstruct the history of life on Earth. Pinning down when specific events occurred is often tricky, though. For this, biologists depend mainly on dating the rocks in which fossils are found, and by looking at the “molecular clocks” in the DNA of living organisms.
There are problems with each of these methods. The fossil record is like a movie with most of the frames cut out. Because it is so incomplete, it can be difficult to establish exactly when particular evolutionary changes happened.
Modern genetics allows scientists to measure how different species are from each other at a molecular level, and thus to estimate how much time has passed since a single lineage split into different species. Confounding factors rack up for species that are very distantly related, making the earlier dates more uncertain.
These difficulties mean that the dates in the timeline should be taken as approximate. As a general rule, they become more uncertain the further back along the geological timescale we look. Dates that are very uncertain are marked with a question mark.
the skin covering the human body consists of 2 layers.
I believe the correct answer is mRNA. Dicer is a part of RNase III which leaves double stranded RNA and pre-microRNA into short double stranded RNA fragments called small interfering RNA and microRNA respectively. The Dicer facilitates the activation of RNA induced silencing complex (RISC), which are essential for RNA interference. The RISC has a catalytic component argonate, which is an endonuclease capable of degrading mRNA. siRNAs are specfic to the mRNA sequence unlike miRNAs which are not completely complementary to the mRNA sequence.
Answer:
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