EARLY EARTH
Identify the relationship between the conditions on early Earth and the origin of organic molecules.
- What does identify mean?
- Structure your answer. Learn the content before you write an answer.
- Key words
- Be succinct
Early Earth was formed approximately 4.5 billion years ago. During its early years the Earth underwent many changes. Clouds of water vapour that originally surrounded the Earth began to form the seas. The seas were quite warm. There were only one or two large land masses. Volcanoes were continually active spewing ash and lava into the atmosphere. The original atmosphere was thought to only contain hydrogen and helium. However due to the lack of gravity these gases escaped the atmosphere. This gave rise to the secondary atmosphere which contained hydrogen, carbon monoxide, carbon dioxide, nitrogen, methane and ammonia. There was no free oxygen making this environment anoxic. These gases on the early Earth had the main constituents to form organic molecules (C, H, and O) which in turn led to the origin of organic molecules around 4 billion years ago. Once these organic compounds arose primitive cells began to emerge around 3.5 billion years ago.
Discuss the implications of the existence of organic molecules in the cosmos for the origin of life on earth.
- What does discuss mean?
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Some scientists have suggested that our DNA and RNA (C, H, O, N, P) could have come from outer space. This theory arose due to the fact that early Earth was bombarded with meteorites/asteroids for approximately 500 years. Fred Hoyle stated that small microbes and other micro-organisms came to Earth from outer space via meteorites/asteroids. Astronomers have detected carbon compounds in meteorites and comets, however there is not enough concrete evidence to support that the cosmos was the soul cause for the origin of life.
OTHER KEY FACTS:
- Chemicals make up cells.
- Proteins: (made up from building blocks of 20 amino acids) C, H, O, N, P, S.
- 74 amino acids have been found in meteorites.
- 75% of molecules detected in space are organic
- Fossil bacteria in Martian rocks
- Organic materials widespread in cosmos
Describe two scientific theories relating to the evolution of the chemicals of life and discuss their significance in understanding the origin of life.
- What does describe and discuss mean?
- Underline key words
- Research your answer before you decide to answer the question.
Chemosynthetic theory- this theory states that the origin of life arose from the organic molecules that were present on the early Earth. Early Earth contained many simple elements which formed simple compounds. These compounds contained the building blocks for life. Scientists believe that these compounds must have converted into the building blocks of life under the right conditions, and therefore the beginning origins of life.
Scientists have replicated early Earth conditions to identify whether or not chemicals from the early Earth yielded any life. Their findings are quite significant and have led to a better understanding of the origins of life.
Outer space theory- states that the origins of life originated from outer space and made their way to Earth via meteorites/asteroids as elements, compounds and even simple cells. Space material has been found to contain organic molecules. These molecules make up living matter. The outer space theory shows the possibility that life arose from space material coming to earth. This theory is also significant in our understanding of the origin of life.
Discuss the significance of the Urey and Miller experiments in the debate on the composition of the primitive atmosphere.
- What does discuss mean?
- Outline the experiment performed by Urey and Miller
- Link what they found to the origin of life
- Link what they found relating to the composition of the early atmosphere
Urey and Miller simulated the early conditions on Earth. The main reason for this was to test the chemosynthetic theory that chemicals from the early Earth could covert to biological chemicals under the right conditions. Miller set up an apparatus that was symbolic of the primitive atmosphere. The atmosphere chamber contained the early gases including methane, carbon dioxide, ammonia, nitrogen, hydrogen and water vapour. An electrical discharge was passed through the atmosphere chamber to simulate energy. When samples were taken from the fluid they found organic molecules, the main chemicals that make up living matter. Other experiments used UV light which yielded nitrogenous bases, ribose, amino acids and nucleotides (genetic material).
This experiment has not proved that biological compounds were formed from non-living matter under these early Earth conditions. The biological compounds could have evolved from the sea floor from volcanic vents or even from heat and chemical energy. However this experiment does prove that non-living matter under the right conditions can form organic matter (living), and thus supporting the chemosynthetic theory.
Identify changes in technology that have assisted in the development of an increased understanding about the origin of life and the evolution of living things.
Things to consider: - What does identify mean?
- Underline key words
- Know what the question is asking
- Write an answer in which you understand
There have been many changes in technology which have assisted in the development of an increased understanding about the origin of life and the evolution of living things. Technology changes include seismology (seismographs), radiometric dating, microscopy and biological studies.
SEISMOLOGY – Geologists have developed our understanding of the Earth and its structure through the use of seismology, which is the study of pressure and shock waves produced by earthquakes. Seismographs are produced to record the wave patterns and strength of such crustal movement. There is such a large amount of interest in seismology/seismographs because the changing structure of the surface layers may have influenced the origin and evolution of life.
RADIOMETRIC DATING: This type of technology uses radioisotopes to date rocks and fossils. Radiometric dating is an important piece of technology as it identifies how old the Earth may be as well as dates the origin of life and the evolution of living things.
MICROSCOPY and BIOLOGICAL STUDIES. Developments in microscopy, particularly the electron microscope, have led to a new understanding of structures at the molecular level. Biochemical analysis particularly of DNA, have enabled scientists to undertake comparative studies of different organisms. Genetic engineering techniques continue to help scientists to understand how change can take place in living organisms and thus we can better understand the relationship between organisms and their possible evolutionary pathways.
The use of these new technologies has led to a better understanding of the origins of life and the evolution of living things.
Identify the major stages in the evolution of living things, including the formation of:
- organic molecules
- membranes
- procaryotic heterotrophic cells
- procaryotic autotrophic cells
- eucaryotic cells
- colonial organisms
- multicellular organisms
Things to consider: - What does identify mean?
- Underline key words
- Know what you are going to write before you write your answer.
- Use scientific language
There are many stages which have contributed to our understanding of the evolution of living things. These stages are as follows:
The formation of organic molecules (4.0 BYA)
Complex organic molecules formed in water on the early Earth, from pre-existing chemicals.
The formation of biological membranes (4.0 – 3.5 BYA)
Membranes developed to isolate and protect the system of large complex organic molecules which evolved to include nucleic acids and became capable of self-replication.
Procaryotic heterotrophic cells (3.5 – 2.5 BYA)
First cells with simple structures. These cells used up biological molecules in their environment for sustainability.
Procaryotic autotrophic cells (2.5 – 2.0 BYA)
First type of cells which used energy from the environment to survive. If autotrophs did not evolve life might not have evolved.
Eucaryotic cells (1.5 BYA)
These cells evolved and contained a membrane bound nucleus and cell organelles. Believed to initially evolve from procaryotes.
Colonial organisms (1.5 BYA)
Multicellular organisms may have originated when daughter cells became bound together after cell division to form an aggregation of similar cells or colony. Stromatolites provide an example of this both as fossils and as present-day colonial cells.
Multicellular organisms (1.5 – 0.5 BYA)
There are two methods as to how multicellular organisms evolved one being that the unicellular organism underwent many repeated cell divisions without cytoplasmic division, or the cell underwent cytokinesis. This would have led to the multicellular organism having many cells each with a specialised function. Each cell with a different function is dependent on other cells. However the organism functions as a whole.
Describe some of the palaeontological and geological evidence that suggests when life originated on Earth.
Things to consider:
- What does describe mean?
- What does palaeontological and geological mean?
- Be succinct in your answer and include scientific terminology
The study of rocks and fossils can provide us with the evidence for early life forms and their activities. Firstly palaeontological evidence refers to fossils. Fossil evidence is scarce in ancient rock with the abundance of fossils being mainly found in the past 600 million years. The earliest fossils found are of two types: microfossils which are similar to present day anaerobic procaryotes and stromatolites which are made up of cyanobacteria. These two types of fossils suggest that life may have originated approximately 3.5 bya.
Geological evidence is the study of rocks and the Earth’s crust. The first cells were heterotrophic. After time autotrophic cells emerged to feed heterotrophs as well as to photosynthesise. As we know oxygen is a by-product of photosynthesis. The oxygen had a dramatic effect on the Earth. The oxygen produced did not at first build up in the atmosphere but was taken up by rocks. These oxidised rocks can be seen today in the ancient banded iron and red bed rock formations (2.8 – 2.0 BYA). These rocks have also led scientists to hypothesise about when life first originated on Earth.
Explain why the change from an anoxic to an oxic atmosphere was significant in the evolution of living things.
Things to consider:
- What does explain mean?
- Underline key words
- Understand the question before you write an answer, be succinct and use scientific terminology.
The change from an anoxic to an oxic atmosphere was significant in the evolution of living things. Firstly oxygen began to build up in the atmosphere after most free oxygen had been absorbed by surface rock. Some of this oxygen reacted with U.V. light to form ozone. This in turn enabled the ozone layer to form high in the atmosphere. The ozone layer then acted as a shield and protected organisms from damaging U.V. light. This protecting enabled living things to colonise the land.
We will now look at explaining the change
CAUSE / EFFECT· The change in atmosphere from anoxic to oxic.
· Oxygen levels increased in the atmosphere.
· Evolution of photosynthesis and respiration (oxygen required) / · Anaerobic organisms declined due to the presence of oxygen which affected their growth and metabolism. Photosynthetic organisms began to evolve.
· Living systems developed. Used oxygen to produce chemical energy. Aerobes produced energy using respiration. Greater metabolic activity. More active. Result was increase in size/complexity of organisms.
· Life on Earth changed forever. Plants and animals became more complex. Presence of oxygen in the atmosphere limits the formation of complex organic molecules such as amino acids.
We can now see that these changes in the atmosphere were significant in the evolution of living things.
Process and analyse information to construct a timeline of the main events that occurred during the evolution of life on Earth. (Pg 161 of text)
Things to consider:
- What does process and analyse mean?
- What does construct mean?
- Relate the question to the evolution of life.
10 BYA the universe began5 BYA the galaxies began to form
4.5 BYA The Earth was formed
4 BYA The early evolution of organic molecules. Biological membranes evolve to protect organic molecules
3.5 BYA procaryotic heterotrophs form. First known stromatolites found in WA
2.5 BYA procaryotic autotrophs emerge and begin to photosynthesise
2.3 BYA first cyanobacteria found in stromatolites, production of oxygen by these cyanobacteria by the means of photosynthesis
2 BYA Anoxic to Oxic atmosphere
1.5 BYA first eucaryotic cells appear in turn forming colonies
1 BYA multicellular organisms evolve
600 MYA most animal phyla present, diverse algae
500 MYA diversification of animal phyla. First jawless fish
440 MYA first bony fish, plants and animals evolve on land
400 MYA first insects and amphibians
345 MYA extensive forests, first reptiles
290 MYA many types of insects, increase in reptiles, amphibians decline
225 MYA first dinosaurs, first mammals, diverse marine invertebrates
180 MYA diverse dinosaurs, first birds
138 MYA flowering plants and mammals diversify
66 MYA increasing numbers of birds, mammals, flowering plants
2 MYA humans evolve
Discuss the ways in which developments in scientific knowledge may conflict with the ideas about the origins of life developed by different cultures.
Things to consider:
- What does discuss mean?
- Identify what you need to write before answering the question.
- What cultures are we going to consider?
Discussion:
Gather first hand or secondary information to make observations of a range of plant and animal fossils.
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- Underline key words
- Answer all questions
(Refer to the photocopied worksheet, from Heinemann to answer this dot point)
Identify data sources, gather, process, analyse and present information from secondary sources to evaluate the impact of increased understanding of the fossil record on the development of ideas about the history of life on earth.
Things to consider:
- What does identify, gather, process, analyse, process and evaluate mean?