00:03To analyse past climates, scientists drill deep into the ice and extract tube-shaped sections
00:10called core samples. In a glacier or a polar cap, ice has accumulated over a long period of time,
00:17sometimes over hundreds of thousands of years. When collecting samples, scientists prefer to
00:22position themselves on a dome where flow is slowest and the ice stratification is most intact.
00:27They then bore into the ice with a core drill which can reach a depth of three kilometres and extract
00:33samples which can measure up to four metres long. For very deep cores, scientists must make hundreds
00:39of round trips over several days to retrieve all the samples. Later, the sample is opened or crushed
00:46using various methods in order to analyse air bubbles that have been trapped in the ice for
00:51millennia. Their compositions provide information about the atmosphere thousands, even hundreds of
00:56thousands of years ago. By compiling data from cores, we can trace the Earth's history, learning
01:02about ice ages and warm periods, major volcanic eruptions, magnetic field reversals and changes
01:09in atmospheric CO2 levels.
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