Life on the early earth Flashcards
1
Q
How old is the earth?
A
4.5 billion years old.
2
Q
What is data for the age of the earth derived from?
A
derived from looking at the ratios of radioactive
elements - typically by using uranium-lead dating
3
Q
What do fossil preserve?
A
Traces or remains of organisms
4
Q
Why do the most commonly found fossils arise?
A
due to replacement of organic material after
burial by minerals dissolved in water in the
ground and recrystallization.
5
Q
In exceptional circumstances fossilisation reveals…
A
…fantastic detail
6
Q
What are microorganisms the key to?
A
the key to all life.
7
Q
OUr perception of life tend to be…
A
anthropocentric - we notice life at our scale.
8
Q
Why are microorganisms the key to all life?
A
they lie at the base of food chains and are essential in ensuring elements such as oxygen, carbon, and nitrogen are available to plants and animals.
9
Q
What is life dominated by?
A
life is dominated by microorganisms
10
Q
when was the origin of the earth?
A
origin of the
earth (~ 4.5
billion years
ago)
11
Q
WHen was the origin of life?
A
origin of life
(~ 3.5 billion
years ago)
12
Q
When was the origin of multicellular life?
A
Origin of
multicellular life
(~ 1 billion
years ago)
13
Q
When was the origin of humans?
A
200 thousand years ago
14
Q
How does complexity change throughout the modern world?
A
increasing complexity.
15
Q
What were key moments in evolution?
A
- the origin of life
- the oxygenation of the atmosphere
- the origin of eukaryotic cells
- the origin of multicellular organisms
- the ‘Cambrian explosion’
- the colonisation of the land by complex organisms
16
Q
What did Millers experiment aim to do?
A
to recreate conditions that existed on the primordial earth
17
Q
What was generated in Millers experiment?
A
amino acids.
18
Q
Describe millers experiment.
A
Miller’s famous experiment used electricity to provide energy to a mixture of gases in a closed system. After incubating the mixture for a period of time he discovered that some of the building blocks of life – amino acids – had been formed.
19
Q
What was used in Millers experiment?
A
gases - methane, hydrogen, ammonia, water vapour.
energy source
boiling water
trap to collect products
20
Q
whats a problem of millers experiment?
A
it is now thought that the
atmosphere of the earth was quite different
21
Q
Whats a long popular theory of how life arose?
A
‘primordial soup’
22
Q
Explain primordial soup theory.
A
- sea acts as a trap collecting amino acids, nucleotides, and other organic molecules as they form.
- these were then thought to have joined up to make macromolecules (protein and DNA) which led to life
23
Q
WHats a problem with the primordial soup theory?
A
One problem is that the ‘soup’ was unlikely
to have been concentrated enough. More of a
‘weak broth’ really…
24
Q
Whats a alternative hypothesis more widely accepted than the primordial soup theory?
A
life arose around hydrothermal vents in the deep oceans.
25
Explain the hydrothermal vents theory of how life arose.
hydrothermal vents presented a far more concentrated solution of organic molecules. They also give off energy in the form of heat which is essential for life to develop. These ‘black smokers’ are found on the ocean floor now and have ecosystems that are independent of the sun
26
Describe the earliest cells.
the earliest cells may have
been little more than ‘bags’
enabling higher concentrations
of nutrients to build up
high concentration of organic
molecules enabling the
construction of ‘biologically
useful’ molecules
27
all current life requires...
...cells.
28
one possibility is that the first cells were...
...lipid vesicles
29
Why are lipid vesicles formed?
because fatty acids have one
end that likes to react with water (hydrophilic)
and another that likes to ‘hide’ from water
(hydrophobic).
This means that fatty acids will aggregate into a
sphere in aqueous solution.
30
Whats the problem with simply invoking lipid vesicles to collapse and form cells?
The problem with simply
invoking lipid vesicles to
collapse and form cells is that
they are unstable and…
where do the phospholipids
come from?
31
Whats a more recent suggestion on how lipids form cells?
More recently
suggested that early cells
were bounded by an
amphiphilic protein
membrane or by a
combination of lipids and
amino acids
32
What was early life dominated by?
early life on earth was dominated by the
simplest organisms we know today - prokaryotes
on the left are fossil prokaryotes from a rock
formation over 2 billion years old
above are three electron micrographs of
prokaryotes all of these prokaryotes are types of
bacteria
33
Prokaryotes are the simplest...
form of cells that we see living today.
34
What are the important components of the prokaryotic cell which i need to remember?
plasma membrane
DNA in the nucleoid
Ribosomes
Cytoplasm
35
function of plasma membrane in prokaryotes?
(made of lipids which encloses the cell)
36
FUnction of DNA in the nucleoid in prokaryotes?
encodes all the information it needs to make
protein
37
Function of ribosomes
make proteins
38
function of cytoplasm
where all the chemical reactions necessary for life occur
39
whats the size of prokaryotes?
1-10 um
40
Where are the oldest known fossils found?
found in a rock formation
called the Apex chert
41
WHeres the apex chert?
australia
42
What does the apex chert contain?
they consist of filaments of
cells ‘strung’ together and
date to 3.5 billion years ago
43
What do the apex chert fossils closely resemble?
the Apex chert fossils closely
resemble organisms today
which are called Cyanobacteria. These bacteria photosynthesise
44
What does it mean when a bacteria photosynthesises?
(using sunlight as an energy
source to convert CO2
into
useful carbon compounds)
45
What did analysis of the first cyanobacteria microfossils show?
analysis of the first cyanobacterial microfossils suggest these to be already
complex – is there any evidence of older life?
46
do we need a microscope to see evidence of microbial life?
No. You can see evidence of microbial life from a fossil stromatolite.
47
How old are fossil stromatolites?
3 billion years old.
48
What do fossil stromatolites consist of?
consists
of many thousands of layers of
individual bacteria
49
Living stromatolites can be found today though they are...
...very uncommon
50
Why do stromatolites persist in shark bay - australia?
they persist
because they live in extremely
salty conditions which nothing
else can tolerate
51
Many of the first organisms on earth would have
originated in an atmosphere that was...
...devoid of oxygen
52
For bacterial organisms such as cyanobacteria, oxygen is very...
...highly toxic
53
Some of the extremely old bacteria...
...persist to this day – existing in environments which are free of oxygen such as mud at the bottom of stagnant ponds or the soil.
54
What are bacteira termed as?
Anaerobes.
55
How long ago did photosynthesis begin?
3.5 billion years ago
56
How long ago did significant levels of oxygen arise in the atmosphere?
it
took until 0.5 billion
years ago to have
significant levels of
oxygen in the
atmosphere
57
What happened to most of the first oxygen produced?
most of the first oxygen produced
reacted with dissolved iron in the
oceans and was deposited as a
sediment at the ocean floor.
These banded-iron formations are
characteristic of rock from that
period
58
What occurred in regards to xygen 0.5 billion years ago?
around 0.5 billion years
ago significant amounts
of oxygen build up in
the earth’s atmosphere
59
What does photosynthesis by cyanobacteria result in?
photosynthesis by
cyanobacteria results in
free oxygen being
released into the
atmosphere or
dissolved in water
60
Original ideas about how different species were related divided life into...
‘kingdoms’ – animals,
plants and ‘protists'
61
What does the five kingdom model and the tree of life suggest?
progression
62
WHat does the five kingdom model split life into?
Plantae
Fungi
Animalia
Protista
Monera
63
Based on examinations of dna sequences, it is now clear that there are...
...three domains of life.
64
When did separation between the three domains occur?
Very early in evolutionary history
65
What are the three domains of life?
Bacteria, Archaea, Eukarya
66
What were bacteria and archaea originally classed as in the "three domains of life" model?
both archaea and bacteria
were originally classed as
prokaryotes but they
exhibit some fundamental
differences
67
Both of *what* were originally classed as prokaryotes in the three domains of life model?
both archaea and bacteria
68
What are prokaryotes?
Prokaryotes are organisms whose cells lack a nucleus and other organelles. Prokaryotes are divided into two distinct groups: the bacteria and the archae.
Most prokaryotes are small, single-celled organisms that have a relatively simple structure.
69
What is a eukaryote?
Eukaryotes are organisms whose cells contain a nucleus and other membrane-bound organelles. There is a wide range of eukaryotic organisms, including all animals, plants, fungi, and protists, as well as most algae. Eukaryotes may be either single-celled or multicellular.
70
Compare eukaryotic cells to prokaryotic cells.
eukaryotic cells are larger and more complex than prokaryote cells yet they have a
similar basic structure – with one big difference.
71
What are the parts of eukaryote cells that i need to know?
1. plasma membrane
2. DNA
3. ribosomes
4. cytoplasm
5. organelles – e.g. mitochondria
72
function of plasma membrane in eukayrotes?
membrane compartmentalization to allow for the formation of enclosed environments for specific metabolic processes
controls the passage of organic molecules, ions, water, and oxygen into and out of the cell
73
function of DNA in eukaryotes?
encodes all the information it needs to make
protein in a nucleus.
surrounded by a membrane
74
Where is dna stored in eukaryotes?
in a nucleus
75
Where is dna stored in prokaryotes?
in a nucleoid.
76
Examples of organelles in eukaryotes?
mitochondria, chloroplasts, the endoplasmic reticulum, the Golgi apparatus, and lysosomes.
77
Do prokaryotes have organelles?
No
78
What are organelles?
An organelle is a membrane-bound subcellular structure that has one or more specific jobs to perform in the cell, much like an organ does in the body
79
What are mitochondria?
Mitochondria are membrane-bound organelles present in the cytoplasm of all eukaryotic cells, that produce adenosine triphosphate (ATP), the main energy molecule used by the cell.
80
How are eukaryotes thought to have evolved?
- eukaryotes are now thought to have
evolved after an ancestral prokaryote
engulfed a smaller, oxygen-breathing
bacteria
- the bacteria persisted and reproduced with
the parent cell
- the relationship benefitted both cells
- the oxygen-breathing bacteria became the
mitochondria
- in photosynthetic eukaryotes a further
endosymbiotic event occurred
a photosynthetic bacteria was engulfed
which became the chloroplast
81
Size of single celled eukaryotes?
single-celled eukaryotes can
be quite large – Amoeba
species can grow up to
1mm in diameter and are
thus just about visible to
the naked eye
82
Where are paramecium species found?
Paramecium species
are also commonly
found in freshwater –
they feed by ingesting
bacteria
83
What is the single-celled eukaryote Giardia thought to resemble?
thought to resemble the
ancestral eukaryote as it
lacks mitochondria –
however it is now known
that mitochondria have been
lost in this species
84
Many of the single celled eukaryotes are...
...photosynthetic.
85
Where does the photosynthetic ability of single-celled eukaryotes derive from?
the photosynthetic ability of these cells derives from the
endosymbiosis of chloroplasts
86
Multicellular plants are thought to have evolved from...
...single celled eukaryotes - algae
87
What are some examples of single-celled eukaryotes [plant cells]?
Chlamydomonas reinhardtii
Euglena species
88
Sinle-celled non-photosynthetic organisms similar to amoeba are likely to have given rise to...
...multicellular animals
89
What gave rise to multicellular animals?
single-celled non-photosynthetic organisms are likely to have given rise to multicellular animals
90
Plants, fungi, and animals are all...
...independently evolved multicellular organisms
91
why did multicellularity evolve?
size... you can vastly increase how big you are and therefore can compete
more successfully for food
92
What is the problem for multicellular organisms?
- The problem that individual single-celled organisms face is that there is a size limitation
due to surface area to volume constraints
- The surface area does not keep pace with increases in volume and it becomes harder for
diffusion or osmosis across surfaces to take place efficiently enough
93
Why (in some sense) is multicellularity almost as old as life itself?
cyanobacteria form colonies though these are ‘clonal’ (they derive from the
same original cell)
94
In Dictystellium, what is the response to starvation?
single celled organisms
aggregate and form a
‘slug’ which migrates to a
better food source
some differentiation
occurs during formation
of the fruiting body
95
How did Volvox evolve multicellularity?
Volvox is thought to have
evolved multiceullarity by a
colonial method as with
Dictyostelium.
96
What does Volvox resemble?
rather than
resembling amoebae the
vegetative cells closely
resemble those of
Chlamydomonas
97
What chemical fossils were found in Oman and what did they show?
steroids found in sedimentary rocks
in Oman which could be the
remains of sponges from 635
million years ago
98
How long ago did Ediacaran fauna dominate the sea?
600 million years ago.
99
How common are ediacaran fossils and what happened to the organisms?
fossils are rare – all organisms
seem to have been soft-bodied
100
What might *some* ediacaran be related to?
some may be related to
cnidarians (jellyfish) but most
have no living descendants
that we recognise
101
WHat was the cambrian explosion a period of?
a period of experimentation in body plan
- some survive, some go under.
102
What happens when oxygenation of the atmosphere reaches significant levels?
oxygenation of the atmosphere
reaches significant levels –
animals with skeletons appear
– arthropods, chordates,
molluscs – fossils more
abundant
