How did that arrowhead end up underground in the first place?
A Native American left it on the surface hundreds of years ago.
Dinosaur bones, on the other hand, are millions of years old -- some fossils are billions of years old.
To determine the ages of these specimens, scientists need an isotope with a very long half-life.
The most widely known form of radiometric dating is carbon-14 dating.
This is what archaeologists use to determine the age of human-made artifacts. The half-life of carbon-14 is only 5,730 years, so carbon-14 dating is only effective on samples that are less than 50,000 years old.
Choose: No Frames Layout Choose: Human Evolution Frames .
I have integrated this web page on human evolution into an electronic text, " Nature's Holism - Holism.
This is because sediments easily accumulate in water environments (lakes, streams, oceans).
1) Which of the following factors weaken(s) the hypothesis of abiotic synthesis of organic monomers in early Earth's atmosphere? the relatively short time between intense meteor bombardment and the appearance of the first life-forms 2.
the lack of experimental evidence that organic monomers can form by abiotic synthesis 3.
But this sediment doesn't typically include the necessary isotopes in measurable amounts.
Fossils can't form in the igneous rock that usually does contain the isotopes.