Sediments swirl off the Yucatán


Sixty-six million years ago, an asteroid or comet about 14 kilometers wide crashed into Earth. It hit what is now Mexico’s Yucatán Peninsula, which then lay at the bottom of a shallow sea. The impact has been catastrophic. It triggered tsunamis, started forest fires and ejected a cloud of ash and dust that circled the globe, blocked the sun and cooled the climate. The collision and its aftermath ultimately killed 75% of all life on Earth, including the dinosaurs.

The story was pieced together from evidence scattered around the world, which pointed to a 180-kilometer-wide crater near the coastal town of Chicxulub on the north coast of the Yucatán Peninsula. The town of Mérida, located inland south of Chicxulub, appears as a gray-brown area near the top of the image, which was acquired by the Moderate resolution imaging spectroradiometer (MODIS) on NASA Earth satellite on October 31, 2021.

Chicxulub Crater, which now rests partly on land, is the best-preserved large impact crater on Earth. Over the millions of years since the impact, the crater was buried in thick layers of limestone. However, remains of the crater are still visible on the surface.

A 250-kilometer-long arc of chasms marks the edge of the crater. Those chasms, called cenotes, supplied fresh water to the ancient Mayan inhabitants of the peninsula. The region also lacks surface water due to the karst landscape (soluble limestone). Because rainwater is slightly acidic, surface water dissolves and seeps through the limestone bedrock, creating dissolution pits, cenotes, and caves, as well as the world’s longest underground river. .

When these thick layers of limestone erode, chalky sediments flow onto the wide, shallow Yucatán Plateau. In this image in natural colors, the sediment eddies are visible off the north and west coasts of Campeche Bay.

Sediments scatter light and this reflectivity gives water a characteristic color when viewed from space. When floating near the surface, the sediment appears as a muddy brown, but as it sinks and disperses, the color changes to shades of green and light blue. When shallow coastal waters are agitated by winds, tides, storms or currents, the sediment on the seabed can be resuspended, giving the seawater a white or pale blue appearance. Some of the color can also come from phytoplankton – microscopic, plant-like organisms – which sometimes float to the surface in bloom large enough to be seen from space.

Image from NASA Earth Observatory by Lauren Dauphin, using MODIS data from NASA EOSDIS SPEAR and GIBS / worldview. Sara E. Pratt’s Story.


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