Absolute dating isotopes
When scientists date rocks from our planet this way, the oldest dates they find are 4.5 billion years.
By dating the lava flows above and below a fossil find, scientists can put exact boundaries on the maximum and minimum age of that fossil.
With radioactive dating, scientists can now get within a few percentage points of the actual date.
They know this because they have been able to accurately date lava flows that happened recently enough for their dates to be known historically, such as the eruption of Mount Vesuvius at Pompeii.
147] has highlighted the fact that measurements of specimens from a 1801 lava flow near a volcano in Hualalai, Hawaii gave apparent ages (using the Potassium-Argon method) ranging from 160 million to 2.96 billion years, citing a 1968 study [Funkhouser1968].
In the particular case that Morris highlighted, the lava flow was unusual because it included numerous xenoliths (typically consisting of olivine, an iron-magnesium silicate material) that are foreign to the lava, having been carried from deep within the earth but not completely melted in the lava.
Here is one example of an isochron, based on measurements of basaltic meteorites (in this case the resulting date is 4.4 billion years) [Basaltic1981, pg. Skeptics of old-earth geology make great hay of these examples.
For example, creationist writer Henry Morris [Morris2000, pg.
In the second half-life, half of the remaining atoms transition, leaving one quarter of the original parent material.
Other isotopes are unstable because the different number of neutrons interacts with the other atomic components in such a way that, over a period of time, the isotope changes into some other atom.