Transcript Evolution of Life on Earth

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
Water on
Earth’s
surface
Earth without free oxygen
Banded iron formations commonly
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,
are alive in
Australia today.
Shark Bay, Australia
History of Atmospheric Oxygen
The presence of FeS2 and UO2
set upper limits because oxygen
would have produced other
oxides from U and Fe
From Lunine 1999 based on Kastings (1991)
Cambrian Period (505-570 Myr)
Rocks ½ 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.
The profile of a ~100 km crater of an
impact that occurred 66 million yrs ago.
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.
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
130,000 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 (130,000
yrs), just 0.003%
the age of Earth.
No HS skulls occur
in earlier rocks.
DNA variation
among humans
indicate an age of
130,000 years.
In comparison,
dinosaurs &
stramatilites lasted
2% and 78% the
lifetime of Earth.
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