feg)                             TABLE 1-2 Geologic Time and Significant Events in Earth History                            few				
	Condensed into one Calendar Year			
Years before Present	Event	Days since January 1              Date and Time		
10,000	Tee Age ends	364.9		December 31, 11:58:51 p.m.
] .6 million	Ice Age begins	364.9		December 31, 8:57:11 p.m.
4 million	First humans	364.6		December 31, 4:11:29 p.m.
53 million	First horses	360.8		December 27, 7:04:10 p.m.
66 million	Dinosaurs become extinct                                359.8			December 26, 6:18:47 p.m.
] 15 million	First flowering plants	355.9		December 22, 9:00:00 a.m.
145 million	First birds	353.5		December 20, 11:52:10 a.m.
222 million	First mammals	347.4		December 14, 9:14:05 a.m.
230 million	First dinosaurs		344.8	December 11, 7:08:52 p.m.
360 million	First amphibians		336.4	December 3, 10:26:02 a.m.
430 million	First land plants		330.9	November 27, 9:07:50 p.m.
510 million	First fish		324.5	November 21, 12:46:57 p.m.
700 million	First multicellular animals		309.5	November 4, 10:57:23 a.m.
3.6 billion	Oldest fossils		71.0	March 13, 1:08:52 a.m.
4.6 billion	Earth formed	0		January 1, 12:00:00 a.m.
				
c
CO
Q-
O N O C Q) O
O
'o
N O
o; co Q-
Quaternary
CD O)
o 0
(D
c
CD O) O Q CO
CÖ
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Pennsyl-vanian
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Paleocene
0.01
1.6
5
24
37
58
66
Missis-sippian
Devonian
Silurian
Ordovician
Cambrian
144 208 245 286
320
360 408 438 505 570
2,500
3,{
4,600
^> FIGURE 1-19 The geologic time scale. Numbers to the right of the columns are ages in millons of years before the present.
> Figure 8-12 (left) a block
diagram of a hypothetical area whose geologic history can be reconstructed by applying the various relative dating principles.
i> FIGURE 8-I3 (below) (a) Beds A, B, C, D, E, F, and G are deposited. (b) The preceding beds are tilted and faulted, (c) Erosion, (if) Beds J, K, and L are deposited, producing an angular unconformity, (e) The entire sequence is intruded by a dike. (/") The entire sequence is uplifted and eroded. (g) Beds P and Q are deposited, producing a disco n form ity (N) and a nonconformity (O). (/() Dike R intrudes. (/) Lava (S) flows over bed Q, baking it. (/') Bed T is deposited.
L-x_	-f   "*		
K—■	O		-7^ ,
J-7-			w) V
%^
		
	AHV'	
		tip
		
		
		
		
A—'		
	a) Deposition	
(i) Lava flow
(h) Intrusion
85
CD
•g    86
1  87
E
2     88 <
$> FIGURE 8-19 Radioactive decay
series for uranium 238 to lead 206.                       °"
Radioactive uranium 238 decays to its
stable end product, lead 206, by eight
alpha and six beta decay steps. A                           91
number of different isotopes are
produced as intermediate steps in the
decay series.
90
92
Pb
214
Bi
214
Pb210
Pb
206
p0218           ~Q
P0214
• Rn
222
• Ra226
Pa
234
# Th23°
U
234
r^Bi210 t
Po
210
Alpha decay step Beta decay step
Lead
-  Bismuth Polonium
-  Astatine
-  Radon Francium
-  Radium
-  Actinium
- Thorium
-  Protactinium
-  Uranium
100
o
Q.
CD ČO
E
03
I
Q.
O C
o
50-
25-
Ö    12.5
o    6.25
ŕ 3.125
Mineral at time of crystallization
Atoms of parent element Atoms of daughter element
Mineral after one half-life
Mineral after two half-lives
Mineral after three half-lives
Time Units
TABLE S-!  Five of the Principal Long-Lived Radioactive Isotope Pairs
Used in Radiometric Dating
Isotopes
Parent
Daughter
Half-Life of Parent (Years)
Effective Dating Range (Years)
Minerals and Rocks That Can Be Dated
Uranium 238
Uranium 235 Thorium 232 Rubidium 87
Potassium 40
Lead 206
Lead 207 Lead 208 Strontium 87
Argon 40
4.5 billion
704 million 14 billion
48.8 billion
1.3 billion
10 million to 4.6 billion
10 million to 4.6 billion
100,000 to 4.6 billion
Zircon
Uraninite
Muscovite
Biotite
Potassium feldspar
Whole metamorph i c or igneous rock
Glauconite        Hornblende
Muscovite         Whole volcanic rock
Biotite
I
Cosmic radiation
Neutron capture
\
Carbon 14
C!4 is absorbed    .
y along with C Vl and
C13 into the tissue
of living organisms
in a fairly constant
ratio.
íl               IX
MtirfrtliiMiÉlIiirtlIilliilimftÉilliliiirt
Mé m
MMiHtUi
When an organism dies, C14 converts back to N14 by beta decay.
Carbon 14
Beta decay
Beta*v particle
Nitrogen 14
Proton
O Neutron
^* FIGURE 8-24 The carbon cycle showing the formation dispersal, and decay of carbon 14.
^ FIGURE 8-26  In the cross-dating method, tree-ring patterns from different woods are matched against each other to establish a ring-width chronology backward in time.
C. This beam came from an old house
^-This date obtained by counting back from bark of A through B
D
JD
EE
3E
Fi   :
GE
|G
HE
H
3)J
Specimens taken from ruins, when matched and overlapped as indicated, progressively extend the dating back into prehistoric times.