The Eocene epoch began 55 million years ago with a rapid increase in global temperatures, the Eocene warming. The warm period lasted for 20,000 years. It was so warm during this period that ocean water at the poles supported tropical life forms. Climatologists have proposed several theories to explain the Eocene warming.
Some scientists have hypothesized that changes in the ocean currents caused the warming. It is well documented that at the start of the Eocene, many ocean currents drastically changed direction, perhaps because of a change in the position of the continents. Deep-water currents in the Atlantic Ocean, flowing in new directions, transported warm water from the tropics toward the poles. Proponents of the ocean current theory point to this change as the cause of the Eocene warming.
A second theory proposes that an enormous comet struck Earth and initiated the Eocene warming. When comets strike Earth, they can create atmospheric conditions that lead to an increase in atmospheric temperatures. The comet theory is supported by the discovery of a high concentration of magnetic particles in a thick layer of clay that dates to the beginning of the Eocene. Since comet collisions often deposit magnetic particles in the soil, the clay layer provides good evidence for the comet theory.
A third theory attributes the warming to the release of methane from oceans into the atmosphere. Substantial quantities of methane are usually trapped on the floor of the ocean. However, there is evidence that at the beginning of the Eocene, changes in the oceanic environment caused large portions of the methane to escape. Methane is a potent greenhouse gas, and once it escapes into the atmosphere, it can cause a rise in atmospheric temperatures and, therefore, events such as the Eocene warming.
Summarize the points made in the lecture, being sure to explain how they challenge the specific theories proposed in the reading passage.
In the lecture, the professor casts doubt on the reading passage’s idea that changes in ocean currents, a comet impact, or methane release explain the Eocene warming. The professor asserts that none of these theories provides a convincing explanation for the warming event.
Firstly, the passage claims that ocean current changes transported warm water toward the poles and caused the Eocene warming. By contrast, the professor asserts that computer models show these currents could only move a limited amount of heat, much less than needed to explain the extreme warming observed during the Eocene.
Secondly, the author of the passage points out that a high concentration of magnetic particles in clay provides evidence for the comet theory. However, the lecture notes that recent research shows the magnetic particles were produced by primitive bacteria, not by a comet collision. Without the magnetic particle evidence, the comet theory loses its support.
Lastly, the reading states that methane released from the ocean floor into the atmosphere could have caused the warming. On the contrary, the professor contends that if methane were responsible, the warming would have occurred thousands of years after the methane release. However, geological data show the warming and the methane release happened at the same time, not with the expected delay, weakening this theory as well.
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