Answer:

1.The earliest time that life forms first appeared on Earth is at least 3.77 billion years ago, possibly as early as 4.28 billion years, or even 4.41 billion years—not long after the oceans formed 4.5 billion years ago, and after the formation of the Earth 4.54 billion years ago.

2.a calcareous mound built up of layers of lime-secreting cyanobacteria and trapped sediment, found in Precambrian rocks as the earliest known fossils, and still being formed in lagoons in Australasia.

3.These two pathways, with the same effect on RuBisCO, evolved a number of times independently – indeed, C4 alone arose 62 times in 18 different plant families.

4.Oxygen fluctuations stalled life on Earth

Given the importance of oxygen for animals, researchers suspected that a sudden increase in the gas to near-modern levels in the ocean could have spurred the Cambrian explosion.

5.Dinosaurs roamed the earth for 160 million years until their sudden demise some 65.5 million years ago, in an event now known as the Cretaceous-Tertiary, or K-T, extinction event.