1. How abundant was oxygen in the early atmosphere?
The earth’s early atmosphere contained only small amounts of free oxygen, produced by the reaction of water vapor with sunlight. The oxygen rich atmosphere that developed later and on which oxygen breathing life now depends was result of the origin and spread of organisms capable of photosynthesis.
2. What evidence do scientists have that the oxygen content of our atmosphere has increased since the earth’s origin?
By looking at the rustiness of ancient rocks, scientists attempt to trace the evolution of oxygen in the atmosphere.
3. Why is oxygen more abundant in the atmosphere today?
spread of organisms that did photosynthesis.
4. What are stromatolites?
stramolites are laminated mound like structures that generally form in shallow water through the growth of microscopic blue-green algae and bacteria.
5. What do scientists think is implied by the presence of stromatolites in Precambrian rock?
May of the algae and bacteria that build modern stramolites are photosynthesis.
6. What is ozone and how is it produced?
Ozone screens out most of the ultra violet radiation from the sunlight. Ozone forms through the action of ultra violet radiation on oxygen in the upper atmosphere and many scientist reason that their layer could have formed only after oxygen from photosynthesis began to accumulate.
7. Why is the ozone important to life today?
The ozone is important to life because it acts as a shield from the harmful effects of direct radiation.
8. What effect did increased levels of oxygen in the atmosphere have on early life forms? Created a threat because of the early life form because their environment polluted by their oxygen reducing neighbors whose internal chemistries could resist oxygen toxic free.
Banded Iron Formation
1. What is banded iron
Rock that contains oxidized iron, iron chemically combined with oxygen.
2. When did these formations become common?
Formed in ancient years. About 2.2 billion years ago.
3. What is the significance of these formations?
Pebbles and cobbler show that liquid water was present on the surface of the earth, and ion oxides indicate free (uncombined) oxygen was also present, though at very low levels.
The Oldest Rocks: Remnants of a Youthful Earth
1. How old are the oldest rocks on earth?
The oldest rocks on earth date back to 3800 million years ago.
2. What evidence of life do these ancient rocks contain?
the presence of oxygen to the activity of oxygen producing organisms, therefore life was far along.
3. Is this evidence great enough to allow scientists to conclude that life indeed existed during this period? No because the physical processes in the atmosphere could also have produced free oxygen and in some rocks residues that contain carbon have a make up similar to living matter but these residues to may have purely chemical origin.
The Earliest Traces of Life
1. When do scientists think life originated on Earth?
Between 4600 million years ago to 3500 million years ago.
2. What are the oldest fossils and how old are they?
The oldest fossils on record are stromatolites, which date back to 3500 million years ago.
1. When did the first cells with nuclei appear?
3800 million years ago
2. Fossils of multicellular animals are from what time period?
The fossils of multicellular animals date back to the Precambrian time period.
3. In what era did all of these events take place?
The events listed above took place at the beginning of the Cambrian period to the end of the Paleozoic era.
Origin of Life
1. What elements are most prevalent in living organisms?
The six elements most prevalent in living organisms are carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur.
2. Were these elements present in the...