dating is a method used to determine the age of rocks by comparing them with
those in other layers. Relative Dating is based on the law of superposition,
which states that younger layers of rock are deposited on top of older layers.
Dating uses the decay of radioactive isotopes to measure the age of the rock.
Recall that an isotope is a form of an element that has the same atomic number
but different mass number. The method requires that the half-life to be known.
The half-life is the amount of time it takes for half of the original isotope
to decay. An example of a radioactive isotope that is used to help distinguish
fossils is Uranium 238. When testing a rock sample, scientists calculate the
ratio of the parent isotope to the daughter isotope to determine the age of the
sample. Isotopes cannot be used to date rocks that contain fossils. Radioactive
isotopes for radiometric dating can only be found in igneous or metamorphic
first 4 billion years of Earth’s History make up the Precambrian. This is more
than 90% of Earth’s entire history. It stretches very widely on the geologic
time scale. During this eon, Earth was formed and the first life form appeared.
You might think how oxygen would be present since there were no trees. The
answer is in autotrophic prokaryotes. They enriched the atmosphere with oxygen.
Eukaryotic cells also emerged, and by the end of the 4 billion year period, the
first animals emerged. There was also extensive glaciation during the time.
Food chains were short and was dominated by animals that consumed tiny
particles suspended in the water.By
studying other planets and the environment around Earth, scientists believe
that Earth has began its life about 4.6 billion years ago. Due to gravity, the
densest elements accumulated towards the core of the planet. 500 million, years
later, a crust has formed much like the crust that forms on top of lava. This
crust was rich in lighter elements. Scientists believe that Earth’s younger
surface contained a lot of volcanic features and intense heat. If there were
any life among Earth at that time, it would have probably been consumed by the