History of Life on Earth The Geological Time- Scale
Agenda or Summary Layout The Geological Time-Scale 1 2 3 The Geological Time-Scale The Beginning of Life Cambrian Explosion
The Geological Time-Scale The Geological Time-Scale The Earth s Geological Time Scale
The Geological Time-Scale What does it mean? Remember that the history of life took place millions and millions of years ago. Therefore scientists had to develop a time scale that uses bigger units than century. This time scale is called the Geological Time-Scale.
The Geological Time-Scale How does it work? This time scale divides the Earth s history into three main eras. These eras are the Paleozoic, Mesozoic and the Cenozoic. This goes back to about 543 million years ago. These eras are then divided into time periods. There are about 13 time periods like Triassic, Jurassic and Neogene. Then the Cenozoic time period is divided into smaller time periods called an Epoch. Before the Cambrian period is described as the Pre-Cambrian Time.
Something for you to do. Can you answer this question? 1. Describe the time period in which you live using the geological time-scale. 2. How long ago did the Holocene Epoch begin? 3. Can you describe 10 000 years in million years?
Solution The answer is 1. Holocene Epoch of the Quaternary Period of the Caenozoic Era. 2. 10 000 years ago. 3. 0.01 million years ago
History of life on earth Page 282-285
The Geological Time-Scale How did life begin? Scientists believe that the Earth began about 4-6 million years ago. It was a huge ball of fire with rocks and burning gas. When it cooled, gases were released from the inside it. Hydrogen, methane, ammonia and nitrogen were the main gases. Water vapor was also present. It formed from the water that was found on the Earth s surface.
The Geological Time-Scale How did life begin? These gases together with the water vapour formed the atmosphere. Notice that there is no oxygen. However some scientists believed that oxygen was present in very small quantities. A Russian scientist A.I Oparin and an English scientist J. B. S Haldane put forward an hypothesis about how life began in the 1920 s. They hypothesized that uv light and lightening changed these gases into organic molecules.
The Geological Time-Scale How did life begin? These organic molecules were proteins and fatty acids. These molecules combined to form the cell membranes. It is believed that this was how cells were formed. Fossil evidence suggests that cells existed from about 3.4 billion years ago. However there is no fossil evidence on how they formed because gases and liquids do not form fossils.
The Geological Time-Scale How did life begin? The hypothesis put forward by Oparin and Haldane was tested by Stanley Miller in 1953. Miller worked under the guidance of Harold Urey at the University of Chicago. In his experiment he pumped out the air of the closed apparatus. The air was replaced with water vapour, methane, hydrogen and ammonia.
The Geological Time-Scale How did life begin? At that time Earth experienced violent storms, Miller recreated this by heating the water and passing the gases past a high voltage electric spark. The electric spark represented the lightening. After a week the contents of the flask had turned red. These contents were then removed and studied. Miller found amino acids and other organic compounds.
The Geological Time-Scale How did life begin? However there were scientist that did not support Miller s findings. They believed that primitive Earth did contain oxygen and that the levels of oxygen were high enough to prevent the formation of organic compounds.
Life During the Pre-Cambrian Times. Before 543 million years ago The pre-cambrian times occurred before the Cambrian Period. Scientist often describe the time or year in which a particular organism evolved or arose as the year or time period in which the first fossil appeared. The chart alongside is based on these fossil findings. 0.5 billion of years ago Earliest Animals developed just before the Cambrian Period. 1.5 billion years ago The earliest eukaryotes belonging to Kingdom Protista. They were mainly unicellular. Around 2.5 billion years ago Amount of oxygen in atmosphere increased due to the photosynthet ic bacteria. About 3.5 billion years ago earliest life forms were prokaryotes. They were photosynthet ic. About 4.5 billion years ago the formation of the Earth.
The information shown in the chart in the can be translated into a time line. 0.5- Earliest Animals 1.0- Billions of 1.5- Earliest prokaryotes years ago 2.0-2.5- Accumulation of oxygen 3. 0- } different types of bacteria 3.5- Prokaryotes (photosynthetic bacteria) 4.0- Possible origin of earliest life forms 4.5- Formation of Earth
Geological time scale The last 542 million years is called the Phanerozoic Eon many multicellular organisms Phanerozoic Eon divided into 3 major time units: Palaeozoic (ancient life) Mesozoic (middle life) Caenozoic (recent life) Within these 3 eras there are 11 geological periods with distinctive fossil records
Geological time scale Rocks and fossils can be dated with an accuracy of plus or minus 1 million years or less The first 2 eras ended with catastrophic extinctions which is why the life forms in each era are so different
The Cambrian Explosion start of the Phanerozoic Eon The animal explosion. This period lasted for about 38 million years It started 543 million years ago and lasted until about 505 million years ago. The most notable happening during this period was the explosion of the animal groups. The animals suddenly appeared in the first 5 to 20 million years. These animals appeared on Earth in a very short period of time.
The Cambrian Explosion The fossil record shows the major animal groups appeared as follows: the coelenterates sponges molluscs arthropods chordates annelids echinoderms 520 million years ago 540 million years ago 536 million years ago 513 million years ago 524 million years ago 520 million years ago 518 million years ago
End of the Cambrian times to the modern period History of life from the end of the Cambrian period to the Holocene Epoch The epoch in which we now live is called the Holocene epoch. We shall now look at the history of life from the end of the Cambrian time until the modern epoch. Based on fossil records scientists think that the following organisms appeared as follows: fish about 438 million years ago amphibians about 380 million years ago reptiles about 385 million years ago birds about 180 million years ago mammals about 150 million years ago humans about 150 000 to 200 000 years ago
The Cambrian Explosion Several possible reasons for the animal explosion Global glaciation killed most species which left many empty niches for organisms to evolve More oxygen means aerobic respiration could now be supported Increased supply of organic food from plankton and nekton Macrophage evolved which started the arms race between predator and prey. Varied ecosystems developed in the shallow seas and included autotrophs, heterotrophs, filter feeders, deposit feeders and decomposers.
Plants and animals invade the land The first vascular plants evolved by the start of the Devonian Period. They had tough vascular tissue for support and transport of water and food, a cuticle to prevent water loss, stomata for gaseous exchange and spores for dispersal. No true roots and leaves. Limited animals, mainly arthropods (mites, millipedes, scorpions) that stayed in moist areas By the end of the Devonian Period (60 MA later) true plant, arthropods, fish and amphibious tetrapods were part of the terrestrial ecosystems
End of the Cambrian times to the modern period Human history The first bipedal animals of the human family appeared about 2 million years ago. According to the fossil records there were many species of these bipedal ape- like ancestors. They showed a gradual increase in height, brain size and a gradual flattening of the face. It is believed the earliest ape-like ancestors of humans lived millions of years ago in Africa.
Terminology These are the terms you must know Geological Time-Scale: the time scale that is used to trace the history of life. Eras: these are the time period in which the Earth s history is divided into. Time periods: are the smaller time periods that the eras are divided into Epoch: is the smaller time period into which the time periods of the Caenozoic Era is divided into. Pre-Cambrian Time : is the period before the Cambrian period.
Something for you to do 1. The three main Eras of Earths history. A. Paleozoic, Mesozoic and Caenozoic B. Holocene, Paleozoic and Triassic C. Quaternary, Mesozoic and Triassic D. Caenozoic, Triassic and Paleozoic
2. The periods of the Caenozoic Era is called A. Era B. Time period C. Epoch D. Cambrian
3. The gases found on Earth 4-6 billion years ago A. Oxygen, methane and nitrogen B. Hydrogen, carbon and oxygen C. Hydrogen, methane and ammonia D. Nitrogen, oxygen and water.
4. The two scientists that hypothesized that uv light and lightening changed the gases found on earth into organic molecules are A. Miller and Urey B. Oparin and Haldane C. Oparin and Urey D. Miller and Oparin
5. The scientist that tested the above hypothesis was called A. Miller B. Oparin C. Urey D. Haldane
6. The earliest life forms of the pre-cambrian times were A. Prokaryotes B. Eukaryotes C. Humans D. Fish
7. The earliest eukaryotes developed about years ago. A. 0.5 B. 1.5 C. 2.0 D. 4.5
8. The organism that was responsible for releasing oxygen into the atmosphere during the pre- Cambrian times were A. Fungi B. Plants C. Photosynthetic cyanobacteria D. bacteria
9. The first organisms of the animal kingdom appeared thousand years ago. A. 200 B. 150 C. 610 D. 300
10. The Holocene belongs to the period. A. Quaternary B. Neogene C. Palaeocene D. Triassic
11. The Neogene period is a part of the era. A. Caenozoic B. Mesozoic C. Paleozoic D. None of the above.
12. The Cretaceous period began about million years ago. A. 4500 B. 0.01 C. 144 D. 208
13. The gas that was in extremely small quantities or completely absent when life on Earth began. A. Methane B. Hydrogen C. Ammonia D. Oxygen
14. The gas that increased in the Earth s atmosphere when the photosynthetic bacteria developed. A. Methane B. Hydrogen C. Ammonia D. Oxygen
15. The geological time period that we are now living in. A. Quaternary B. Neogene C. Palaeocene D. Triassic
16. The geological time period in which the major groups of animals appeared. A. Cambrian B. Triassic C. Jurassic D. Permian
17. The geological time period when the dinosaurs flourished. A. Cambrian B. Triassic C. Jurassic D. Permian
18. The oldest phyla of invertebrates that appeared on Earth. A. Coelenterates B. Sponges C. Molluscs D. Arthropods
Solution: 1. A 2. C 3. C 4. B 5. A 6. A 7. B 8. C
9. C 10. A 11. A 12. C 13. D 14. D 15. A 16. A 17. C 18. D