Final answer:
Limestone reefs and salt deposits are essential in reconstructing Earth's climatic history because they contain environmental indicators of ancient climates, such as fossils and specific sediment chemistry. These geologic features allow us to infer past temperatures and conditions from deposits formed in historically warm shallow seas.
Step-by-step explanation:
Limestone reefs and salt deposits are critical in reconstructing Earth's climatic history because they can provide insights into ancient climates. These deposits, found in sediments, carry environmental indicators which allow geologists to infer past climate conditions. Limestone, particularly, forms from the remains of marine organisms such as clams and corals in warm, shallow parts of the ocean, which tells us both about the past location of oceans and the temperatures at the time of formation.
In the past, marine life that thrived in warm conditions left behind fossils that are now found in areas far from current ocean boundaries. These fossils indicate that such areas were once below sea level and typically in much warmer environments. Furthermore, analyzing the chemical makeup of sediments and fossils allows geologists to interpret details about past temperatures and precipitation, assisting in painting a picture of the Earth’s historical climate.
However, it is not accurate to say that all such deposits occurred between 200 and 400 million years ago, nor that they pinpoint the exact locations of old subduction zones. Instead, these deposits and structures are more broadly useful for understanding the environmental conditions over vast periods of Earth's history.