THE ALVAREZ ASTEROID IMPACT THEORY
There are a lot of theories about why the K-T (Cretaceous-Tertiary) extinction occurred,
but a widely accepted theory (proposed in 1980 by physicist Luis Alvarez and his son
Walter Alvarez, a geologist), is that an asteroid 4-9 miles (6-15 km) in diameter hit the
Earth about 65 million years ago. The impact would have penetrated the Earth's crust,
scattering dust and debris into the atmosphere, and causing huge fires, volcanic activity
, tsunamis, and severe storms with high
winds and highly acidic rain . The impact could have caused chemical changes in the
Earth's atmosphere, increasing concentrations of sulfuric acid, nitric acid, and fluoride
compounds. The heat from the impact's blast wave would have incinerated all the life forms
in its path.
The dust and debris thrust into the atmosphere would have blocked most of the sunlight for
months, and lowered the temperature globally.
Those organisms that could not adapt to the temperature and light changes would die out.
Since plants' energy is derived from the sun, they would likely be the first to be
affected by changes in climate. Many families of phytoplankton and plants would die out,
and the Earth's oxygen levels may well have dramatically decreased, both on land and in
the oceans, suffocating those organisms which were unable to cope with the lower oxygen
levels.
Major changes in the food chain would result from all of these these environmental
upheavals. The herbivores (plant eaters) who ate those plants would starve soon after the
plants died. Then, at the top of the food chain, the carnivores (meat eaters), having lost
their prey, would have to eat each other, and eventually die out. Their large carcasses
must have provided smaller animals with food for quite a while.
LOCATION OF THE IMPACT CRATER
There are many impact craters on Earth. A 120-mile-wide (180 km), 1-mile-deep (1600 m)
impact crater, Chicxulub, is found at the tip of the Yucat�n Peninsula, in the Gulf of
Mexico. This crater dates back to 65 million years ago, and is probably the site of the
K-T meteorite impact. Evidence of K-T period tsunamis all around the Gulf of Mexico has
been found.
CHEMICAL EVIDENCE FOR THE THEORY
In the clay layer from the Cretaceous-Tertiary (K-T) boundary, scientists have found
chemical evidence that supports the Alvarez impact theory. The K-T layer consists of the
sedimentary deposits that accrued from the end of the Cretaceous period to the beginning
of the Tertiary period. It is divided into two layers, the Magic Layer (3 mm thick) and
the Ejecta Layer (2 cm thick).
Siderophiles - The Rare Earth Elements Os, Au, Pt, Ni, Co, Pd, and Ir, are Siderophile
Elements. Their abundance in the lower K-T layer is indicative of an asteroid impact.
Iridium (Ir) has been found in the K-T layer around the world. The discovery of a
100,000-years-thick layer of iridium in the K-T boundary in New Zealand, Denmark, and
Italy. Iridium is rare on Earth except near the Earth's center, but relatively abundant in
chondritic meteors (stony meteors with chondrules, spherical blobs of silicates which
pre-date planetary formation). A meteoritic origin of this iridium layer seems likely.
This layer became known as the iridium anomaly. Tektites - Tektites are quartz
grains which are vaporized under intense heat and pressure, and cool into glass beads with
no crystalline structure. Tektites were probably formed during a meteorite or comet
collision. Tektites are abundant in the K-T layer. Shocked quartz - When quartz is
put under extremely high pressure, it can cleave in parallel planes. Shocked quartz is
found at nuclear bomb sites and known meteorite impact areas. Shocked quartz is abundant
in the K-T layer. Stishovite (Silicon Dioxide) - a form of quartz created under
conditions of high heat and pressure. It is used as an indicator of meteor impact. It has
been found in abnormally high abundance in the K-T layer. Most likely formed during a
massive collision. Glass beads - Kenneth Miller has discovered a two-inch layer of
glass beads in the K-T layer near the Bass River in New Jersey, USA, supporting Alvarez'
theory.