Earth_Magazine_October_2017

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E

gyptian mummies provide

archaeologists with a tanta-

lizing window into ancient

Egyptian culture. And now

they are offering up their DNA.

Molecular biologists have long been

skeptical about recovering intact DNA

from such remains. “The hot Egyptian

climate, the high humidity levels in

many tombs, and some of the chemi-

cals used in mummification techniques

contribute to DNA degradation and are

thought to make the long-term survival

of DNA in Egyptian mummies unlikely,”

said senior author Johannes Krause of

the Max Planck Institute for the Sci-

ence of Human History in Germany, in

a statement released with the paper in

Nature Communications.

But Egypt’s location as the gateway

between Africa and the Middle East,

and the potential for recov-

ering clues about how

people moved through the

region, drove Krause and

his colleagues to try recov-

ering genetic material from

mummies. They sampled

151 mummified individuals

— some from the archaeolog-

ical site of Abusir el-Meleq

by the Nile River in Mid-

dle Egypt, and some from

museum collections — that

spanned more than 1,300 years of Egyptian

history. To the researchers’ surprise, they

could extract and sequence mitochondrial

DNA from 90 mummies and genomic

DNA from three. Analysis of both types of

DNA revealed that ancient Egyptians were

more closely related to ancient populations

in the Levant, the Anatolian Peninsula

and Europe than Sub-Saha-

ran Africa.

“Our results revise pre-

vious skepticism towards

the DNA preservation in

ancient Egyptian mummies

due to climate conditions

or mummification procedures,” the team

wrote. “The methodology presented

here opens up promising avenues for

future genetic research and can greatly

contribute towards a more accurate and

refined understanding of Egypt’s popu-

lation history.”

Mary Caperton Morton

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O

n average, a cubic meter

of snow weighs less than

100 kilograms, but heavy,

compacted snow can weigh

more than 500 kilograms per cubic meter,

with glacial ice approaching 900 kilo-

grams per cubic meter. In California, as

elsewhere, the weight of winter snow and

spring runoff pushes down on the land-

scape, affecting stresses on fault systems,

which may trigger small quakes. As the

snow melts and the runoff makes its way

downstream, land rebounds, setting off

more small earthquakes.

In a study in Science looking at the

effects of water on mountains in Cal-

ifornia, researchers calculated how

subsurface stresses under mountain

ranges change with the seasonal water

cycle by combining GPS measurements

of seasonal land surface fluctuations with

models of rock mechanics. The team

found that the weight of winter water

in the form of snow and ice pushes the

Sierra Nevada down by about a centime-

ter and the Coast Ranges by about half

a centimeter.

The researchers correlated the

water cycle with a catalog of more than

3,600 small quakes that occurred in the

state between 2006 and 2015, finding

that faults along the eastern edge of the

Sierras experienced more activity in late

spring and early summer, whereas the

San Andreas Fault in the western part of

the state saw an increase in small quakes

under magnitude 2 in late summer and

early fall. The pattern reflects the sea-

sonal redistribution of water in different

regions as well as the nuances — like ori-

entation and stress loading — of individual

faults. The Sierras see more water-related

quakes in the springtime aftermath of

the wet winter months, when heavy

winter snows and high runoff flows are

still weighing down the range, while the

Coast Ranges see more quakes once the

land has started rebounding.

The authors caution that their find-

ings don’t mean that all earthquakes in

California will occur at certain times of

the year. “There is no earthquake season,”

said senior author Roland Bürgmann of

the University of California’s Berkeley

Seismological Laboratory, in a statement.

When it comes to triggering water-af-

fected faults, “it all depends on the details

of the loading, the location of the fault

and the geometry of the fault.”

Mary Caperton Morton

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