Around 56 million years ago, the Atlantic Ocean had not fully opened and animals, perhaps including our primate ancestors, could walk from Asia to North America through Europe and across Greenland. Earth was warmer than it is today, but as the Palaeocene epoch gave way to Eocene, it was about to get much warmer still — rapidly and radically. The cause was a massive geologically sudden release of carbon. During this period called Palaeocene – Eocene Thermal Maximum or PETM, the carbon injected into the atmosphere was roughly the amount that would be injected today if humans burned all the Earth’s reserves of coal, oil and natural gas. The PETM lasted for about 1,50,000 years, until the excess carbon was reabsorbed. It brought on drought, floods, insect plagues and a few extinctions. Life on Earth survived — indeed, it prospered — but it was drastically different.

Question: Based on the above passage, the following assumptions have been made:
1. Global warming has a bearing on the planet’s biological evolution.
2. Separation of land masses causes the release of huge quantities of carbon into the atmosphere.
3. Increased warming of Earth’s atmosphere can change the composition of its flora and fauna.
4. The present man-made global warming will finally lead to conditions similar to those which happened 56 million years ago.
Which of the assumptions given above are valid?

The correct option is 1 and 3.

Let us analyze the validity of each assumption step-by-step based strictly on the provided passage:

Analysis of Assumption 1: "Global warming has a bearing on the planet’s biological evolution."
The passage states that during the Palaeocene-Eocene Thermal Maximum (PETM), a period of rapid and radical warming, animals (perhaps including our primate ancestors) could walk across connected land masses. It notes that the warming "brought on drought, floods, insect plagues and a few extinctions" and that "Life on Earth survived — indeed, it prospered — but it was drastically different." Because the warming led to extinctions and a drastically different state of life (prospering in new ways), it directly influenced the course of biological evolution. Thus, Assumption 1 is valid.

Analysis of Assumption 2: "Separation of land masses causes the release of huge quantities of carbon into the atmosphere."
The passage mentions that "the Atlantic Ocean had not fully opened" and that animals could walk across connected land masses. However, it does not state or imply that the subsequent opening or separation of these land masses caused the release of carbon. The cause of the carbon release is described simply as a "massive geologically sudden release of carbon" without linking it to the separation of land masses. Thus, Assumption 2 is invalid.

Analysis of Assumption 3: "Increased warming of Earth’s atmosphere can change the composition of its flora and fauna."
The passage explicitly states that the PETM warming event caused "drought, floods, insect plagues and a few extinctions" and made life on Earth "drastically different." Extinctions and major shifts in how life prospered directly represent changes in the composition of flora (plant life, linked to environmental shifts like droughts/floods) and fauna (animal life, such as insects and primates). Thus, Assumption 3 is valid.

Analysis of Assumption 4: "The present man-made global warming will finally lead to conditions similar to those which happened 56 million years ago."
The passage draws a comparison of scale, stating that the carbon injected during the PETM "was roughly the amount that would be injected today if humans burned all the Earth’s reserves of coal, oil and natural gas." However, it does not assume or conclude that present human actions will definitely result in burning all reserves or that they will "finally lead" to identical conditions. It is a comparison of potential volume, not a prediction of an inevitable outcome. Thus, Assumption 4 is invalid.

Conclusion:
Since only assumptions 1 and 3 are valid, the correct answer is indeed 1 and 3.