ILLUSTRATED FLORA OF EAST TEXAS - Brit - Botanical Research ...

44 INTRODUCTION/GENERAL GEOLOGY OF EAST TEXAS
FIG.24/LOCATION OF THE MARQUEZ DOME IMPACT STRUCTURE IN LEON CO. AND ADJACENT ROBERTSON CO.THE CENTRAL UPLIFT IS MARKED
AS THE SMALL SHADED CIRCLE WITH THE LARGER CIRCLE APPROXIMATING THE CRATER RIM DIAMETER.(ADAPTED FROM BUCHANAN ET AL.1998 AND
WONG ET AL. 2001; USED WITH PERMISSION OF METEORITICS & PLANETARY SCIENCE).
The consequences of such a tremendous impact (a force estimated at 10,000 times the
world’s nuclear arsenal) would have included vast amounts of debris thrown into the
atmosphere causing temporary darkening and cooling of the earth, ecosystem disruption,
and widespread extinction. The mysterious mass extinction of the dinosaurs, ammonites,
and many other creatures approximately 65 million years ago thus seems to be explained
at least in part. Some scientists, however, believe that extensive volcanism contributed to
the mass extinction. It is estimated that 44% of the genera and 70% of the species of marine
plankton became extinct as a result of the impact and its aftermath. The extinction was
selective, however, with certain marine groups and large terrestrial organisms being especially
hard hit (Alvarez et al. 1980, 1984; Bohor et al. 1984; Alvarez 1986; Bourgeois et al. 1988;
Swisher et al. 1992; Krogh et al. 1993; Hildebrand et al. 1995; Dingus & Rowe 1998, a balanced
overview; Graham 1999, a concise summary; Hildebrand 2002). A striking point
regarding the extraterrestrial impact-mass extinction connection is that our awareness of
this phenomenon is quite recent—dating only from the seminal 1980 Alvarez et al. paper.
While still controversial, this discovery is a major conceptual breakthrough about geological
processes on earth and their effects on the planet’s living organisms.