The geologist time scale was formed when scientists studied rock layers and index fossils worldwide. With this information, they placed Earth's rocks in order by relative age. Later, radioactive dating helped determine the exact age of the divisons in the geologic time scale.
This scale is organized by the 4.6 billion years of earth's history into sections based on important changes seen in the geologic record. The largest intervals are called eons, with each eon containing many millions of years.
In precambarian time the processes that affect Earth's surface have lessened the erosion on the surface. Earth was being hit by meteorites every second. Now there is water erosion and there wasn't back then. The surface changes have lessened over time.
In molecular biology, restriction fragment length polymorphism, orRFLP, is a technique that exploits variations in homologous DNA sequences. It refers to a differencebetween samples of homologous DNAmolecules from differing locations ofrestriction enzyme sites, and to a related laboratory technique by which these segments can be illustrated. InRFLP analysis, the DNA sample is broken into pieces and (digested) byrestriction enzymes and the resultingrestriction fragments are separated according to their lengths by gel electrophoresis. Although now largely obsolete due to the rise of inexpensive DNA sequencing technologies, RFLP analysis was the first DNA profilingtechnique inexpensive enough to see widespread application. RFLP analysis was an important tool in genome mapping, localization of genes forgenetic disorders, determination of riskfor disease, and paternity testing.
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