13-2 The Age of the Earth Modern Biology

FOCUS Some evidence collected by scientists indicates the Earth is more than 4 billion years old There is also a great deal of evidence that shows organisms have changed over time. We needed to come up with a method of determining the age of the Earth and its inhabitants.

Which layer of soil is oldest? Why?

Evidence in Stone Read Evidence in stone pg. 272-273 What did those people who thought that the Earth was only a few thousand years old use as the basis of their argument? Major geological features had been produced suddenly by catastrophic events

What was Hutton’s proposal? James Hutton geologist 1788 Rocks and elements had been changed gradually by the elements and natural forces…therefore, the Earth must be much older than a few thousand years.

What important argument did Lyell make? Charles Lyell geologist 1830 Scientists must explain past events in terms of events and processes that they could observe themselves.

Clock in rocks What are fossils? Preserved remains of ancient organisms Geologists use rocks like we use clocks…how? Geological time scale Look at layering (relative age) Radioactive dating (numeric value)

Content: Radioactive Dating: Radioactive elements - decay or break down into nonradioactive elements at a very steady rate. Half-life - unit of measure of radioactive decay = the length of time for half of the radioactive atoms in a sample to decay

Each radioactive element has a different half-life K-40 = 1.3 b.y. decays into Ar-40 U-238 = 4.5 b.y. decays into Pb-206

Absolute dating Absolute dating tries to determine an actual age for a rock. Scientists have divided Earth’s history into units called eras using this radioactive clock. Eras are divided into periods Periods are divided into epochs

Through radioactive dating and the examination of rates of geological processes scientists have estimated that the Earth is about 4.6 billion years old.

Review How do scientists use the decay of radioactive elements to date the Earth’s rocks? How do positions of rock layers as well as the decay of radioactive elements enabled scientists to set up a geological time scale? Dating techniques have shown that the Earth is how old?