National Geographic : 2004 Sep
Astronomical rhythms that affect climate Earth in space 19,000 Earth's orbit arOLJt1d i23,000-year cycle the SLIn and its Earth's t ' red s[)111 orientation in space like an wisteady top, qr idti illy change regularly. Together these I'L111 circle in "JMC( . rhythms are thOLIght to help set the timing of ice ages by affect 141,000-year cycle of sunlight over the, The till of the spill Earth's SUrface. For them decreiises most of the past 2.5 million years, Earth Was 111OVil"Ig " cool and warm cycles 100,000 every 41,000 400,000-year years. years ago, the climate expands wd 100,000 years long. ami more elliwi Cal 400,000-year ice-core record fron'-i More elliptical Vostok Stat'lon, a link between ice ages and astro nornical rhythms. DUring ice ages CO, levels drop. Past Ice cycles For the past 2.5 million years quickly, and the Earth entered a warm inter Earth's climate has cycled through ice ages. glacial period. Scientists believe this timing In the most recent episodes, ice grew over is partly determined by astronomical factors tens of thousands of years until it formed that affect the length of seasons and allow large continental ice sheets. It then retreated ice to build from one winter to the next.