Formation of mountains –
weathering, erosian.
Sedimentary rocks
Dating Rocks
Relative - Absolute
Nicolai Stenonis (1638-1686).
"...at the time when any given stratum was being
formed, all the matter resting upon it was fluid, and,
therefore, at the time when the lower stratum was being
formed, none of the upper strata existed.”
Steno’s Principle of
Superposition
(Prodromus, 1669)
That is, in a sequence of
strata, any stratum is younger
than the sequence of strata on
which it rests, and is older
than the strata that rest upon
it.”
Structure of an atom
Isotopes of an element.
Stable isotopes
Alpha Decay
1 Helium nucleus = 2 neutron + 2 electron.
An atom nucleus looses 1 Helium nucleus
(=alpha decays):
( atom number -2,
atom mass -4)
1 proton = neutron + electron.
An atom nucleus looses an electron
(= beta decay):
1 Neutron  1 proton.
( atom number +1,
atom mass not changed)
An atom nucleus gains an electron:
1 proton  1 neutron.
( atom number -1,
atom mass not changed)
e = N-P; gains a N, loses a P
Radioactive Decay: Loss of an a particle
Samarium
Americium
Plutonium
Uranium
Thorium
Radon
Radioactive Decay: Loss of a b particle.
Rubidium
Rhenium
Iodine
Carbon
Bismuth
chlorine
Radioactive Decay: Gain of a b particle
Potassium
Aluminium
Nitrogen
Carbon
Fluorine
Radioactive decay of Radon-219 to Lead-207.
86Rn
219
83Bi
211
----> 84Po215 ----> 82Pb211 ---->
----> 81Tl207 ----> 82Pb207
Rn: Radon
Po: Polonium
Pb: Lead
Bi: Bismuth
Tl: Thallium
Radioactive element
Half-life
Radon-219
4 seconds
Iodine-131
8 days
Cobalt-60
5 years
Caesium-137
30 years
Carbon-14
5,730 years
Uranium 238
700 million years
Potassium-40
1.25 billion years
Radioactive
Isotope
Decays to
Half-life (years)
Rubidium-87
Strontium-87
49,000,000,000
Rhenium-187
Osmium-187
41,600,000,000
Thorium-232
Lead-208
14,000,000,000
Uranium-238
Lead-206
4,500,000,000
Potassium-40
Argon-40
1,250,000,000
Uranium-235
Lead-207
704,000,000
Samarium-147
Neodymium-143
108,000,000
Iodine-129
Xenon-129
Aluminium-26
Magnesium-26
Carbon-14
Nitrogen-14
17,000,000
740,000
5,730
Radioactive
Isotope
Decays to
Half-life (years)
Rubidium-87
Strontium-87
49,000,000,000
Rhenium-187
Osmium-187
41,600,000,000
Thorium-232
Lead-208
14,000,000,000
Uranium-238
Lead-206
4,500,000,000
Potassium-40
Argon-40
1,250,000,000
Uranium-235
Lead-207
704,000,000
Samarium-147
Neodymium-143
108,000,000
Iodine-129
Xenon-129
Aluminium-26
Magnesium-26
Carbon-14
Nitrogen-14
17,000,000
740,000
5,730
Radio-active Decay K-40, Cl-39, I-129, or
Ra-226:
Accuracy of Radiometric Dating.
1. Several radioisotopes usually occur
together in a rock and decay at
different rates so the dates can be
cross-checked. Nevertheless,
invariably the dates agree.
Accuracy of Radiometric Dating.
2. The half-life of isotopes doesn’t
change when scientists subject them
to extreme temperatures and
pressures or chemical environments.
Radiometric dating of meteorites:
the earth and solar system are 4.6
billion years old.
(Oldest earth rocks - Northern Canada:
4.3 billion years old)
N gains 1 e (e = N-P)
Accuracy of Radiometric Dating.
1. Several radioisotopes usually occur
together in a rock and decay at
different rates so the dates can be
cross-checked. Nevertheless,
invariably the dates agree.
Accuracy of Radiometric Dating.
2. The half-life of isotopes doesn’t
change when scientists subject them
to extreme temperatures and
pressures or chemical environments.
Accuracy of Radiometric Dating.
3. Radiometric dates coincide with
dates obtained by other methods.
c) Carbon dating agrees with the
historic record.
d) Dates of the early paleozoic
coincide with dates calculated
from annual and daily coral rings.
e) Radiometric dates agree with dates
obtained from tree rings.
The Fossil Record
Fossils:
= Remains of past organisms.
 Actual (or petrified) body (parts)
 Excrements (coprolites)
 Gastroliths (stomach stones)
 Imprints (burrows, foot, feathers )
 molecular residues
Coprolites.
Fossilization:
1. Remains in water (river, lake, ocean)
2. Sink to the bottom.
3. Get covered by sediment
Fossils in sedimentary rock!
Exceptions:
a) tar pits (La Brea, Los Angeles)
b) conifer amber
c) sanddunes
Fossilization
TIME
Nature 6 September 2012 vol 489 p22
Xing Xu stands among the remains of duck-billed
dinosaurs in Zhucheng, China
Fossil plant, Carboniferous
Fossilization:
1.
2.
3.
4.
Remains in water (river, lake, ocean)
Sink to the bottom.
Get covered by sediment
Petrified
 Hard > soft body parts
 Aquatic > terrestrial
5. Discovery of fossils
 Exposure on the surface
 Timely removal
The fossil record must be
incomplete
Turtle sex recorded in rock.
Jeholodens: early mammaliformes
(165 million years old)
Nature 1999, 398, p326.
Jeholodens jenkinsi
(165 million years ago)
Eomaia: common ancestor of the Eutheria or placentals.
(About 128 million years old)
Nature 2002, 416 p816.
Eomaia: common ancestor of the Eutheria or placentals.
(About 128 million years old)
Nature 2002, 416 p816.
Eomaia: common ancestor of the
Eutheria or placentals.
(About 128 million years old)
Nature 2002, 416 p816.
Jeholornis: long-tailed, seed-eating
bird of the early cretaceous of China.
(Nature 2002, 418 p405).
What does the fossil record tell?
1. The history of life on earth is
old.
 3.5 bya: first life
Stromatolites
(2 .7 billion years ago)
What does the fossil record tell?
1. History of Life: old
2. Fossils are lacking in the oldest
layers.








3.5 bya: first life (bacteria)
1.5 bya: eukaryotes
0.7 bya: multicellular organisms
0.45 bya:fish
0.35 bya: amphibians
0.30 bya: reptiles
0.20 bya: mammals
0.15 bya: birds
Trilobites
Ordovician, Oklahoma
The fossilized remains of a pregnant mare and fetus (white circle) offer a glimpse into the
reproduction of Eurohippus. Messelensis (47 Mya).
American Association for the Advancement of Science
Science 2014;346:792-793
Published by AAAS
Archaeopteryx:
A transitional
fossil between
reptiles & birds
Intermediate forms
Hippopotamus
(Pakicetus)
Thick, bony wall
around middle ear.
(Ambulocetus)
Large, powerful tail, shorter
legs, fat pad in jaw for
hearing, brakish water
Salt water habitat
(Kutchicetus)
(Rodhocetus)
Nasal opening shifted back,
eyes on side of head
(Basilosaurus)
Tail flukes, very small hindlegs,
Baleen for filtering food
Complete loss of hind legs, nasal
opening reaches position of blowhole
in living whales
Echolocation for hunting
(Dorudon)
Reconstruction of the Tethys Sea in the Middle Miocene (45 Mya)
What does the fossil record tell?
1. History of Life: old.
2. Fossils are lacking in the oldest
layers.
3. Earliest life simpler ; more recent
organisms more complex.
4. Many extinct organisms.
Ordovician
What does the fossil record tell?
5. Ancient organisms were very
different from living species,
resembling modern species
more and more as one moves
up to more recently formed
rocks.
What does the fossil record tell?
6. Fossils in adjacent layers
above and below) were more
similar to each other than to
those found in layers more
widely separated.
Crinoids
What does the fossil record tell?
7. Fossils in the most recently
deposited rocks tend to
resemble modern species
living in THAT area.
Fossil marsupials were found in
profusion only in recent sedimentary
rocks of Australia, and that is where
most modern (extant) marsupials live.
Thylacoleo carnifex (marsupial lion)
What does the fossil record tell?
8. There are no authentically
anachronistic fossils!.
Island Biogeography
Biogeography:
= Distribution of life on earth.
Islands:
Continental Islands
England (0.3 Mya), Japan, Sri
Lanka, Madagascar (160 Mya)
Oceanic Islands:
Hawaii, St. Helena, Juan
Fernandez, Galapagos
Hawaii
Galapagos
St Helena
Juan Fernandez
Archipelago
Juan Fernandez
Archipelago
Juan Fernandez Firecrown
Masafuera
Ravadito
Marine Inguano
Hawaiian Islands
Hawaiian monk seal
St. Helena Wirebird (Charadrius sanctaehelenae)
St. Helena Wirebird (Charadrius sanctaehelenae)
Three facts about oceanic islands:
1. They are missing groups of species
that live on continents and
continental islands
2. The groups that ARE found on
oceanic islands are replete with
many similar species.
3. Often related, but not identical, to
species living on nearby continents.
Compared to other areas of the world,
life on oceanic islands is
UNBALANCED.
Native
Missing
some Plants
Land mammals
some Birds
Reptiles
some Insects
Amphibians
Freshwater fish
Good Colonizers
The End.