Warm-up Week 16 Day 21. Sedimentary rocks record past geological events and ___.

a. changing life forms of the past b. written historyc. Earth’s circumference and d. astronomical

diameter in the past milestones

2. The dating process that places geologic events in proper sequence is referred to as a ____.a. numerical dating c. relative datingb. temporary dating d. radiometric dating

3. Index fossils allow geologists to ____.a. match rocks of the same b. identify organisms that did

age in different regions not leave fossil evidencec. determine rocks’ exact age d. determine why some

organisms became extinct

“Radioactive Dating& Geologic Time Scale”

12.3 & 12.4

Review.

Smallest particle of Element.

“Atoms.”

Nucleus.

• Center of Atom.P+

No

• Outside Nucleus.

E-

“Electron Cloud”

Isotope. • Atom with diff. #’s P+ and No

• Radioactive Decay.

Radioactive Decay

• Isotopes Stable atoms– Parent Daughter

– Release Energy

• “Half-Life”– Time for ½ of nucleus stable.

1. Radiometric Dating– Isotopes decay at constant rate– Calculate “birth” of Parent Isotope

2. Radiocarbon Dating– Carbon-14 isotope

– All living things, from AIR (CO2)

– Ratio of Carbon 12: Carbon 14 gives “death” date.

Review: How do we know…?

1. Relative Dating

2. Fossils

3. Radiometric Dating

4. Radiocarbon Dating

So, Now What?...

Geologic Time Scale

1.Eons

2. Eras

3. Periods

4. Epochs

Evidence Suggests…

Early Earth was VERY different from Earth today.