History of Life on Earth
·
Discussion Notes
·
Vocabulary
·
Overhead transparencies
Discussion Notes
Earth's early atmosphere
probably contained hydrogen cyanide, carbon dioxide, carbon dioxide, carbon
monoxide, hydrogen sulfide, and water. You would probably die within
a few minutes.
Why did early Earth not
have oceans? Because the surface was
extremely hot. It may have taken as
much as 200 to 300 million years.
Miller an Urey's experiments
suggested how mixtures of the organic compounds necessary for life could have
arisen from simpler compounds present on a primitive earth. They created
amino acids! They passed sparks through
a mixture of hydrogen, methane, ammonia and water.
The jump from a primordial
soup to living organisms is the greatest gap in scientific theories of Earth's
early history.
Formation of microspheres
- proteinoid microspheres are tiny bubbles within large organic molecules.
These bubbles have many properties of cells (selectively permeable
membrane, store and release energy).
Evolution of RNA and DNA
- this is still unknown,
but many microbiologists believe RNA existed first (see 17-10 in PH).
Free Oxygen - there was
very little free oxygen in early earth. When
first present, it combined with iron in the brown-colored oceans and formed
iron oxide that fell to the ocean floor. It is the source of iron ore mined today. The absence of iron turned the water to blue-green.
The increase in oxygen
in the atmosphere led some life forms to extinction, while other life forms
evolved new, more efficient metabolic pathways that used oxygen for respiration.
What process added oxygen
to earth's atmosphere? Photosynthetic bacteria.
The endosymbiotic theory
proposes that eukaryotic cells arose from living communities formed by prokaryotic
organisms. This idea was proposed over 100 years ago,
but was not supported until the 1960's.
Paleontologists are scientists
that study fossils. From these fossils, they can infer
structure, diet, environment, and relationship to other organisms (classification).
The fossil record provides
evidence about the history of life on earth. It also shows how different groups of organisms have changed over
time.
Using these and other
data, paleontologists group them in the order in which they lived.
Over 99 percent of all
species that have ever lived on Earth have become extinct.
Meanwhile, over the last
3 billion years scientists believe that unicellular organisms have given rise
to modern bacteria, protests, fungi, plants and animals.
How fossils form in sedimentary
rock:
1. Water carries small particles from existing rocks
to lakes and seas;
2. Rock particles sink to the bottom, burying dead organisms;
3. Weight of upper layers compresses lower layers;
4. Minerals replace all or part of the organism's body;
PLASTER OF PARIS ACTIVITY
Why is the fossil record
considered to be an incomplete record of the history of life? Fossils representing
important events may be missing.
Scientists use molecular
clocks to interpret fossil evidence. Based on the assumption
that mutations occur at a known rate over time (like the ticking of a clock),
the DNA of an organism can diverge from the DNA of its ancestors.
Thereby researchers can assume that more the DNA between living species,
the longer the time since the species shared a common ancestor.
Projects for curious students:
How can data from molecular
clocks show that mammals began evolving before dinosaurs disappeared.
Relative dating allows
paleontologists to estimate a fossil's age compared with that of other fossils
(Index fossils). Index fossils can also be used to date rocks
from different locations.
What assumption do paleontologists
make when using relative dating? They assume
that fossils found in the upper layers of sedimentary rock are younger than
fossils found in lower levels. Human
activities such as mining or other disturbances may cause older layers to
end up on top.
Mummies: Ties to the Past
(Biodetectives video)
Radioactive Dating - scientists
calculate the age of a sample based on the amount of remaining radioactive
isotopes it contains.
Refer to Radioactivity
simulation (100 kernels of corn) and graph
A half-life is the length
of time required for half of the radioactive atoms in a sample to decay.
Pliny Moody - a 12 year
old that discovered the first dinosaur footprints in the US. 1802 Massachusetts. People came to see them, believing they were
footprints from giant ravens from Noah's Ark.
A professor from Amhurst (Edward Hitchcock) determined they were from
large ostriche-like birds.
Probably more than 99.99%
of fossils have been found since Darwin's time (around 1836). How might these fossils have influenced him? What influence did Mendel have on Darwin?
(none, really; Mendel's work occurred whil Darwin was still alive,
but its importance wasn't recognized until the early 1900's.
Geologic Time Scale
The basic divisions of
the geologic time scale are eras. They
are subdivided into periods.
Precambrian Time - about 88% of the earth's history. Very few multicellular fossils from this period
have been found.
Prefixes and suffixes: paleo = early or ancient, meso = middle, ceno = recent, zoic = life
Eras:
Paleozoic - from 544 million
years ago (mya) to 245 mya - Many invertebrates and vertebrates too.
Mesozoic - from 245 mya
to 65 mya - age of the dinosaurs.
Cenozoic - from 65 mya
to the present - age of mammals
Periods:
The names of the periods
often refer to the names of places where fossils from that era are found.
Cambrian comes from Cambria,
the Roman name for Wales. Jurrassic
refers to the Jura Mountains in France. But Carboniferous refers to the large coal
deposits formed during that period.
more on this - develop
posters of each.
Vocabulary (provided with the help of Helen Y.)
Molecular clocks - based on the assumption that mutations occur at
a known rate over time (like the ticking of a clock), the DNA of an organism
can diverge from the DNA of its ancestors.
Thereby researchers can assume that more the DNA between living species,
the longer the time since the species shared a common ancestor.
Radiometric Dating- Dating of objects through the measurement of relative
proportions of certain radioisotopes and the products of their radioactive
decay
Radioisotopes- unstable isotope of an element
Half-life- The number of years it takes for 50% of an original
sample of an isotope to decay
Spontaneous Origin- origin of life through natural chemical and physical
processes
Primordial Soup Model- A hypothesis that suggested that the ocean is filled
with many different organic molecules like soup. The two scientists thought
that these molecules formed spontaneously in chemical reactions activated
by energy from solar radiation, volcanic eruptions, and lightning.
Miller-Urey Experiment- Miller and Urey simulated the early Earth’s conditions
and produced some of life’s basic building blocks. This experiment indicate
that some basic chemicals of life could have formed spontaneously on the early
Earth under conditions like the ones in the experiment.
Bubble Model- Lerman proposed that the key processes that formed
the chemicals needed for life took place within bubbles on the ocean’s surface.
RNA Self-replication- Scientists thought that RNA was the first self-replicating
information-storage molecule. They hypothesized that RNA could also have catalyzed
the assembly of the first proteins.
Catalysts- Chemical agents that change the rate of a reaction
without being consumed by the reaction
Microspheres- tiny, abiotically produced vesicles formed by short
chains of amino acids
Coacervates- the form that aggregates of amino acids, proteins,
and other hydrocarbons came together into in early primordial oceans.
Fossils- preserved or mineralized remains or traces of an
organism that lived long ago
Prokaryotes- Single-celled organism without a nucleus; bacterial
cell
Cyanobacteria- grouop of photosynthetic eubacteria
Eubacteria- one of the two kingdoms of prokaryotes; characterized
by presence of peptidoglycan in cell wall
Archaebacteria- one of the two kingdoms of prokaryotes; differentiated
from eubacteria by various important chemical differences
Eukaryotes- organisms whose cells have a nucleus enclosed by
a membrane
Mitichondria- organelles that produce much of the ATP made by
a eukaryotic cell
Endosymbiosis- theory that proposes that mitochondria are the descendant
of symbiotic, aerobic eubracteria
Protists- members of the kingdom Protista; single-celled eukaryotic
organisms that do not fit into other phyla.
Brown Algae- multicellular protests that form vast underwater
forests in some coastal waters, also called kelps
Cambrian Periods- period of time when most groups of organisms that
exist today seem to have originated from
Mass Extinction- episode during which large numbers of species become
extinct
Rain Forests- Tropical forests that are being destroyed quickly.
They contain more than half of the world’s animal and plant species.
Ozone- The oxygen that was produced by cyanobacterias that
bonded to form O3.
Ozone Shield- an ozone layer that blocks out the dangerous ultraviolet
rays from the sun
Mychorrizae- mutualistic association between a fungus and a plant’s
roots, in w hich the fungus absorbs water and nutrients for the plant and
the plant supplies food to the fungus
Mutualism- symbiotic association in which both partners benefit
Arthropods- members of the phylum Arthropoda, which includes
invertebrate animals such as insects, crustaceans, and arachnids (spiders).
Swamp Forests- forests that existed 320 million years ago that
were dominated by tall, seedless canopy trees and shorter tree ferns.
Vertebrates- animal with a backbone
Evolution of Fishes- fishes started out as jawless creatures about 500
million years ago. Then jaws appeared 430 million years ago and were useful
for biting and chewing. Fishes with jaws were powerful predators.
Evolution of Amphibians- 370 million years ago, vertebrates came out from
the sea and went through many structural changes. They developed lungs, limbs,
and bones.
Evolution of Birds- birds evolved from reptiles. After the fifth mass
extinction, only the smaller birds survived.
Evolution of Mammals- mammals evolved from Therapsids. After the fifth
mass extinction, only the smaller mammals survived.
Continental Drift- the movement on Earth’s land masses over geologic
time. This resulted in the present-day position of the continents.
Creationism- A explanation given by different people that tries
to explain how life on Earth began. I
looked up creationism on the internet and I found this interesting site: http://www.talkorigins.org/faqs/wic.html
Creative Evolution- the belief of this is that the universe is inherently
creative and this creativity is in a evolutionary manner.
History of Life on Earth
Discussion Notes
Early Earth
Earth's early atmosphere
probably contained hydrogen cyanide, carbon dioxide, carbon dioxide, carbon
monoxide, hydrogen sulfide, and water.
Miller an Urey's experiments
suggested how mixtures of the organic compounds necessary for life could have
arisen from simpler compounds present on a primitive earth.
Formation of microspheres
- proteinoid microspheres are tiny bubbles within large organic molecules.
These bubbles have many properties of cells (selectively permeable
membrane, store and release energy).
Evolution of RNA and DNA
- this is still unknown
Free Oxygen - there was
very little free oxygen in early earth.
The endosymbiotic theory
proposes that eukaryotic cells arose from living communities formed by prokaryotic
organisms.
Fossils and the Fossil
Record
Paleontologists are scientists
that study fossils.
The fossil record provides
evidence about the history of life on earth. It also shows how different groups of organisms have changed over
time.
Over 99 percent of all
species that have ever lived on Earth have become extinct.
How fossils form in sedimentary
rock:
1. Water carries small particles from existing rocks
to lakes and seas;
2. Rock particles sink to the bottom, burying dead organisms;
3. Weight of upper layers compresses lower layers;
4. Minerals replace all or part of the organism's body;
Why is the fossil record
considered to be an incomplete record of the history of life?
Scientists use molecular
clocks to interpret fossil evidence.
Relative dating allows
paleontologists to estimate a fossil's age compared with that of other fossils
(Index fossils).
What assumption do paleontologists
make when using relative dating?
Radioactive Dating - scientists
calculate the age of a sample based on the amount of remaining radioactive
isotopes it contains.
A half-life is the length
of time required for half of the radioactive atoms in a sample to decay.
Geologic Time Scale
The basic divisions of
the geologic time scale are eras. They
are subdivided into periods.
Precambrian Time - about
88% of the earth's history.
Prefixes and suffixes: paleo = early or ancient, meso = middle, ceno = recent, zoic = life
Eras:
Paleozoic - from 544 million
years ago (mya) to 245 mya - Many invertebrates and vertebrates too.
Mesozoic - from 245 mya
to 65 mya - age of the dinosaurs.
Cenozoic - from 65 mya
to the present - age of mammals
Periods:
The names of the periods
often refer to the names of places where fossils from that era are found.