Transcript Evolution of Life on Earth - Lunar and Planetary Laboratory

Last Class
Final Quiz: May 6, in class
News:
Detection of extrasolar planet Gliese 581 C, from doppler effect
By the ESO 3.6 m telescope
The planet is 50% larger than Earth.
It is 0.07 AU from star
It orbits a small star (M2.5V red dwarf) 1/3 the mass of the Sun
The star emits 1.3% the luminosity of the Sun
The planet has a temperature that is 0-40 Celsius
Water might be in liquid form at surface.
Evolution of Life
To suppose that the eye with all of its inimitable contrivances
for adjusting the focus to different distances, for admitting
different amounts of light, and for the correction of spherical
and chromatic aberration, could have been formed by natural
selection, seems, I confess, absurd in the highest degree.
- Charles Darwin
Scientific Basis for Evolution:
Anthropology & DNA
Natural selection (Darwin and Wallace 1858) :
traits are inherited, but not perfectly (there are mutations) or changes in the code.
Those with advantageous mutations survive and pass these on; others die off.
Modern Genetics:
Genes are the unit of inheritance, containing segments of DNA, deoxyribonucleic
acid, consisting of chains of nucleotide subunits (Adenosine, Cytosine, Guanosine,
and Thymidine), each of which has a phosphate group, a sugar ring and nucleobase.
Interesting findings:
Human genome has 24 chromozomes with ~3 billion nucleotides.
The chimp’s genome is 98.77% identical to the human genome.
Scientific Basis for Evolution:
Radioactive Dating
Nuclear decay (Beta and alpha decay) changes the number of
protons in an element’s identity. Some elements
decay rapidly to a new daughter element, others
change less rapidly.
Carbon dating (1/2 life: 5730 yrs)
Potassium/Argon dating (1.25 billion yrs)
Water on
Earth’s
surface
2-3 Gyr: Little free oxygen
Banded iron formations occur in
sedimentary rocks 2-3 Gyr old. They
consist of alternating dark bands
(containing FeO) and light bands of
chert (silica and Fe2O3).
They occur from the deposition of
alternately dissolved FeO & chert.
Todays oceans contain oxygen, which
reacts with ferrous oxide (FeO) to form
ferric iron (Fe2O3). This precipitates
out of ocean. The formation of FeO
sediment is not thus likely.
BIFs set an upper limit for the
atmospheric oxygen of less than a few
percent the present value.
The banded structure is thought to occur from
fluctuating densities of bacteria in an ocean. When
bacteria blossoms, it creates oxygen and thus chert,
which falls to the ocean floor. An oxygen depletion
allows for FeO.
Red beds
Earlier than 2 Gyrs ago red
beds occur. These form
when iron is weathered out
of rock in the presence of
oxygen. The oxygen
needed is less than the
present inventory. For
several million years BIF
and red beds overlap,
indicating the presence of
low levels of atmospheric
oxygen.
The Earliest Life
Fossils of layers of
calcium carbon sheets
with concentric spherical
shapes. These limestones
date back 3.5 Gyr, with
less definitive outcrops
dating 3.9 Gyr. They are
formed by colonies of
cyanobacteria.
Chloroplasts are actually
cyanobacteria living in
plant cells
Precambrian (0.5-3.5 Gyr)
Stromatolites, colonies of cyanobacteria, live in Australia today.
History of Atmospheric Oxygen
Stromatolites
The presence of FeS2 and UO2 set
upper limits because oxygen would
have produced other oxides from U
and Fe
vertebrates
From Lunine 1999 based on Kastings (1991)
Cambrian Period (505-570 Myr)
Rocks 1/2 billion years old
differ from early outcrops
because they contain
multitudes of fossils of
various forms of vertebrate
marine life like the trilobite.
Ordovician Period (438-505 myr)
During the ordovician period, creatures resembling today’s
hagfish emerge in the fossils. Rocks formed from fossils of
these worm-like creatures can be seen in the Bright Angel
formation in the Grand Canyon.
A hagfish
Silurian
Period
The emergence of landbased life – both plants and
animals. Fossils of
scorpions and millipedes
are common in these rocks.
Devonian Period (360-408 Myr)
Early sharks
and hingejawed fish can
be found in
these rocks.
Carboniferous
period
(286-360 Myr)
Much of today’s coal
deposits in North
America, Europe and
China were formed
from the
decomposition of flora
from this period.
Permian Period (245-286 Myr)
Rocks deposited in the
Permian period
indicate the first
presence of reptiles.
These include those
that are credited as
being the progenitors
of mammals.
Mesozoic Era
Rocks deposited 245-66 million yrs
ago contain dinosaur bones as well
as the first mammal bones. During
this time the giant continent
Pangaea is breaking up and the
continents are beginning to form.
After the K-T Boundary
Rocks deposited later
than 66 million years
ago indicate a lack of
dinosaur bones. The
abrupt end to massive
dinosaurs is attributed
to the impact of a 10
km meteor.
This event was
perhaps a lucky one
from our point of view,
since it was followed
by the proliferation of
mammals.
Cenozoic Era
From Gibbons, Science, 295, 1214, (2002)
Most skeletons of the
earliest hominids (6-3
million years old) come
from Africa.
This led to the idea
that hominids evolved
in Africa and
progressed with time
to Europe.
The oldest hominid
bones from Europe are
800,000 yrs old.
From Gibbons (2002)
Early Hominids
(3-6 million yrs ago)
Upright gate: after 4 million years ago
Small stature: 4 feet and a bit, 70-110 lbs
Small cranial capacity: ~400-500 cc
Tools: none discovered
Finds: Lucy
Michel Brunet
digging in 6
million yr old
sediment in
Chad.
Lucy, 3.5 million years old
Homo Erectus
(2 – 0.2 million yrs ago)
Taller stature: 5-6 feet and a bit, 120-150 lbs
Larger cranial capacity: ~ 850-1000 cc
Tools: tear drop hand axes
Finds: Java man, Peking man
Neanderthal
(190-27 thousand yrs ago)
Stocky stature: 5 – 5.5 feet
Large size to the muscle attachments
Large cranial capacity: ~ 1500 cc
(exceeds human)
DNA analysis: distinct from humans.
600,000 yrs ago - a common ancestor
with humans.
Finds: La Chapelle-aux-Saints
The marks on
Neanderthal
bones indicate
that the muscle
was separated
from the bone
with stone tools.
Cannibalism?
Images from Science (2002)
Neanderthals
(190,000 – 27,000 yrs ago)
Flaked stones
that fit in wood
handles.
Buried their dead
with spices and
bedding.
Built sturdy huts.
Made flutes!
A flute formed from a femur & 4 remaining holes.
Homo
Floresiensis
(Ebu Gogo)
1 meter high
Lived in Flores until 12,000 yrs ago
Upright posture
6 individuals found
380 cc cranial size (like a chimp)
QuickTime™ and a
decompressor
are needed to see this picture.
Homo Sapiens
(200 thousand yrs ago to present)
Stature: ~5.4 f, 5.9 m feet
Large cranial capacity: ~ 1300 cc
Average weight: 163 f, 190 m
Largest man, Leonid Stadnyk, is 8 ft and 5 inches
Could we date back to earlier or
later times?
No.
Two separate scientific studies indicate that
our species is 200,00 yrs old.
Homo Sapiens
• Modern Anatomy: 200,000 yrs ago
Evidence:
Dates of fossils
Variations in Y chromosome
Mitochondrial DNA
• Art and complex tools: 50,000 yrs ago
• A gene FOXP2 (language & speech) is only
200,000 yrs old. Could such a gene alteration
have changed the behavior of Homo Sapiens?
(Science 2003)
The shapes & sizes
of hominid heads
can be seen to
evolve with time.
Australopithecus vs. Modern
Australopithecus, 4-3 myrs ago
Chimpanzee
Modern human
Cranial Comparisons
Homo Erectus
Neanderthal
Homo Sapiens
Homo Sapiens
200,000 yrs ago
Tall stature
Cranial capacity: ~1350 cc
Art: Cave paintings, Venuses
Oldest paintings: Chauvet (32,000 yrs old)
Peche Merle (15,000 yrs old)
Lascaux (17,000 yrs old)
77,000 yr old artifact
From Blomlos, South Africa
Living quarters
Evidence exists
for tents that
date back ½
million years.
One example is
the remnants of
animal hide
draped over
wooden pilings
found in cave
near Nice
France.
House made of mammoth bones, Mezin Ukraine
A 20,000 year abode
First evidence of
agriculture occurs
in the Fertile
Crescent, and date
back 10,000 years.
From Science
Homo Sapiens have been
around for a short time
(200,000 yrs), just
0.003% the age of
Earth.
Evidence: 1) No HS
skulls occur in earlier
rocks. 2) DNA variation
among humans indicate
an age of 200,000
years.
In comparison, dinosaurs
& stramatilites lasted
2% and 78% the
lifetime of Earth.
Sociology of Science
Public acceptance of evolution
34 counties, 2005
Science vol. 313, pg.765 (2006)
Summary
There is evidence for life on Earth for 3.5
billion years.
Rock formations indicate that little free oxygen
existed in Earth’s early atmosphere.
Fossil records combined with radiometric
dating of sediments indicates that life evolved
slowly (over billions of years) along with the
composition of the atmosphere.
Human evolution can be traced back ~6-4
million years.
Modern humans date back to less than
200,000 years.
Lascaux, France