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Zorluk: OrtaEvaluating the Impact of New Evidence

### Younger Dryas Cooling

The Younger Dryas was a period of abrupt global cooling that occurred approximately 1290012{}900 years ago. Scientists debate the primary cause of this cooling event.

Hypothesis 1
A massive release of freshwater from Lake Agassiz flowed into the North Atlantic Ocean. Because freshwater is less dense than saltwater, this influx capped the warm ocean currents of the thermohaline circulation, halting the transport of heat to the Northern Hemisphere and triggering rapid cooling.

Hypothesis 2
A large comet entered Earth's atmosphere and exploded over North America. The heat and shockwaves from this impact event destabilized the Laurentide Ice Sheet and ignited widespread wildfires, throwing immense dust and soot into the atmosphere that blocked sunlight and caused global cooling.

New Evidence
Researchers analyze marine sediment cores and find that the influx of freshwater into the North Atlantic Ocean—indicated by a distinct drop in salinity and freshwater-associated oxygen isotopes (such as δ18O\delta^{18}\text{O})—occurred approximately 100100 to 150150 years *after* Northern Hemisphere temperatures had already rapidly dropped.

Based on this information, how does the new evidence affect the two hypotheses?

  1. A
    It supports Hypothesis 1 because it confirms that a freshwater influx did occur, and it weakens Hypothesis 2.
  2. B
    It has no effect on Hypothesis 1 because a freshwater influx is still documented, but it weakens Hypothesis 2.
  3. It weakens Hypothesis 1 because the freshwater influx did not precede the cooling, but it does not weaken Hypothesis 2.Cevap
  4. D
    It weakens Hypothesis 2 because the impact would have caused an immediate freshwater influx, but it supports Hypothesis 1.

Cevap

The new evidence weakens Hypothesis 1 because the freshwater influx did not precede the cooling, but it does not weaken Hypothesis 2.
The correct answer states that the new evidence weakens Hypothesis 1 because the freshwater influx did not precede the cooling, but it does not weaken Hypothesis 2. A cause must precede its effect. Because the freshwater influx occurred approximately 100100 to 150150 years after the regional temperatures dropped, it could not have triggered the cooling, which directly weakens Hypothesis 1. Since Hypothesis 2 explains the cooling through atmospheric dust and soot from a comet impact rather than a freshwater-induced ocean current shutdown, the timing of the freshwater influx does not weaken Hypothesis 2.

Adım Adım Çözüm

1
Identify the core causal mechanism proposed by each hypothesis.
Hypothesis 1 claims a freshwater influx caused the cooling. Hypothesis 2 claims a comet impact threw dust/soot into the atmosphere, causing the cooling.
To evaluate the impact of new evidence, we must understand what each hypothesis proposes as the primary cause.
2
Analyze the timing of the freshwater influx relative to the onset of the cooling.
The freshwater influx occurred approximately 100100 to 150150 years after Northern Hemisphere temperatures had already dropped.
A cause must chronologically precede its effect, so the timing of the proposed cause is critical.
3
Determine how this timing affects the validity of each hypothesis.
Since the freshwater influx occurred after cooling began, it cannot be the cause of that cooling, which weakens Hypothesis 1. Hypothesis 2 does not rely on a freshwater influx to initiate the cooling, so this evidence does not weaken Hypothesis 2.
This logical evaluation directly answers the question by matching the timeline to the hypotheses' predictions.

Anahtar Kavram

Evaluating how the timing of geological or climatic events supports or weakens proposed causal mechanisms in conflicting viewpoints.
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Evaluating the Impact of New Evidence

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