Fossils show what kinds of animals and plants lived in certain areas. Scientists also have paleontological evidence-fossils. Their presence under the ocean or on land also tells scientists that glaciers were once present in these areas. Some rocks only form from glacial material. Scientists also have chemical evidence of ice ages from sediments and sedimentary rocks. All of these geographic features on land that currently has no glaciers suggest that glaciers were once there. Glaciers also form elongated oval hills known as drumlins. This sediment sometimes forms mounds or ridges called moraines. They deposit sediment known as glacial till. They scratch and scour rocks as they move. Like clumsy criminals, glaciers leave many clues behind them. Climatologists look for evidence of past climate change in many different places. Many centuries from now, the glaciers may advance again. Many scientists believe we are in an interglacial period, when warmer temperatures have caused the ice caps to recede. Their presence in Antarctica and Greenland suggests Earth is still in a sort of ice age. They have not disappeared completely, however. The ice caps began retreating 18,000 years ago. The most recent Ice Age began about two million years ago and peaked about 20,000 years ago. During these periods, Earth’s temperature decreased, causing an expansion of ice sheets and glaciers. For instance, breadfruit trees ( Artocarpus altilis), now found on tropical islands, grew as far north as Greenland.Įarth has also experienced several major ice ages-at least four in the past 500,000 years. Fossilized plants and animals that normally live in warm environments have been found at much higher latitudes than they could survive at today. For example, fossils from the Cretaceous period (144 to 65 million years ago) show that Earth was much warmer than it is today. As climates change, organisms that live in the area must adapt, relocate, or risk going extinct.Įarth’s Changing Climate Earth’s climate has changed many times. The enormous variety of life on Earth results in large part from the variety of climates that exist.Ĭlimates do change, however-they just change very slowly, over hundreds or even thousands of years. Polar bears have adapted to stay warm in polar climates, while cacti have evolved to hold onto water in dry climates. It has a dry climate.īecause climates are mostly constant, living things can adapt to them. A desert might experience a rainy week, but over the long term, the region receives very little rainfall. For periods of 30 years or more, however, distinct weather patterns occur. Climate is the long-term pattern of weather in a particular area. Weather can change from hour to hour, day to day, month to month or even from year to year.
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