Clues to what ancient climates were like come from all of the following EXCEPTa. ice cores.
b. thickness of rock layers.
c. fossil tree rings.
d. plant pollens.

Answer:

Ice cores

Explanation:

Back in the Cretaceous era, the East Coast was covered with massive ferns, flowers, and unusual fruit trees. Many have long since become extinct or evolved into modern species. But with the help of scientists, such as Dr. James Mickle, knowledge of those plants is starting to be unearthed, providing a window into that primordial era.

In 1971, one of Mickle's colleagues from Texas was digging in the quarry when he found a well-preserved fossil of Leptocycas gracilis, a variety of sago palm that is now extinct. This specimen is the only one found intact, making it an important find in paleobotany.

This plant was similar to sago palms found today, but it was much taller and thinner, a fact that puzzles Mickle and other scientists. It's like finding a fossil of a human ancestor who was 12 feet tall. It's not clear why the palms shrank so much as they evolved.

Mickle's studies show that many of the plants that grew (in North Carolina) in the Cretaceous period are similar to species now found in the tropical climate of the southern hemisphere. This indicates that North Carolina's climate was much hotter in the past, but it is not clear why and how the cooling occurred. "Right now, we're in one of the coldest periods in Earth's history," Mickle said.

By examining the fossil record, Mickle and other paleobotanists have learned that the Earth's climate has changed drastically, with the Triassic period being hot and dry, and the Cretaceous period being cooler and wetter.