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.

Correct Option (D)

Assumption 4 is valid. The passage explicitly draws a parallel between the "massive geologically sudden release of carbon" during the Palaeocene-Eocene Thermal Maximum (PETM) and the "roughly the amount that would be injected today if humans burned all the Earth's reserves of coal, oil and natural gas." This comparison directly implies that current man-made global warming could lead to environmental conditions and consequences similar to those observed 56 million years ago, such as drought, floods, insect plagues, and extinctions.

Regarding Assumption 2, the passage describes the geological configuration of landmasses, noting that "the Atlantic Ocean had not fully opened" prior to the PETM. However, it attributes the cause of warming to "a massive geologically sudden release of carbon" without establishing a direct causal link between the separation of landmasses and this carbon release. Therefore, Assumption 2 is not directly supported by the information provided in the passage.

Incorrect Options:

The validity of the other assumptions, based on the passage, is as follows:

• Assumption 1: "Global warming has a bearing on the planet's biological evolution." This assumption is valid. The passage states that during the PETM, life "survived - indeed, it prospered - but it was drastically different," and mentions "a few extinctions." These outcomes demonstrate that significant global warming events can lead to substantial changes in life forms, influencing biological evolution through adaptation and species loss.
• Assumption 3: "Increased warming of Earth's atmosphere can change the composition of its flora and fauna." This assumption is valid. The passage explicitly notes that after the PETM, life on Earth was "drastically different." This indicates a fundamental alteration in the types and prevalence of plant and animal species, thereby changing the composition of flora and fauna.

While assumptions 1 and 3 are supported by the passage, option D, which includes assumption 4, is identified as the correct answer in the provided solution.