Answer:
Glossopteris and Lystrosaurus
Explanation:
Glossopteris is an ancient plant flora and Lystrosaurus is a fossil fauna, and both are found in many of the landmasses on earth. The Glossopteris flora appeared about 300 to 200 million years back and the Lystrosaurus appeared about 250 million years back on earth. They both existed from the time of late Permian to early Triassic age.
Both these fossils played an important role in understanding the continental drift theory or the plate tectonic theory. This evidence enabled geologists to understand how the continents have moved across the large ocean basin from one place to another and at what rate they are drifting currently. It helped in understanding how the super-continent Pangaea had broken into Laurasia and Gondwanaland, and further broken into the present location of the plates.
The Precambrian era envelopes the major bulk of the history of the Earth, beginning from the creation of the planet approx 4.5 billion years ago and terminating with the origination of composite, multicelled forms of life approximately 4 billion years after.
The Precambrian refers to the earliest of the geologic ages that are signified by the distinct layers of sedimentary rock. The Earth was about more than six hundred million years old when life started. The planet had cooled down from its native molten state, creating a solid crust and oceans formed by water vapor in the atmosphere.
At about three billion years ago, the atmosphere of the Earth was virtually devoid of oxygen. At approximately 2.4 billion years ago, oxygen was discharged from the seas as a waste product of photosynthesis by cyanobacteria. The levels of the gas slowly raised, attaining about 1 percent around two billion years ago.
Approximately 800 million years ago, the levels of oxygen attained about 21 percent and started to breathe life into more composite species. The oxygen-rich ozone layer was also created, protecting the surface of the Earth from the harmful solar radiation.
Explanation:
In thermoplastics, the arrangement of monomeric units is linear and in thermosetting plastics, it is cross-linked. Thermoplastics are usually soft, weak and less brittle, so can get soften on heating and stiffen on cooling. They can be melted, remoulded and recycled easily.
