Question

if the following graph represents the decay of strontium-90 in an igneous rock, what event occurred at 0 years on the horizontal axis ?

Answer 1

When the magama or lava first hardend to become rock.

Answer 2

At 0 years, an event took place which is known as metamorphosis of igneous rock i.e., formation of igneous rocks from melted magma.

Strontium-90 is a radioactive element which undergoes beta decay to form yttrium-90. It has a half life of approximately 28 years and decay energy of 0.546 MeV. This radioactivity is used by geologist to estimate the age of the rock, fossils, meteorites etc. Other radioactive elements used by the geologists are carbon-40, potassium-40 etc.

Radiometric clock is set when the rock was formed in the past i.e., the moment when an ingenious rock was solidified from molten magma.