Innovation 5203: Asteroid impacts significantly altered ancient - TopicsExpress

Innovation 5203: Asteroid impacts significantly altered ancient Earth, 2014. sciencedaily/releases/2014/07/140731150045.htm “New research shows that more than four billion years ago, the surface of Earth was heavily reprocessed as a result of giant asteroid impacts. A new model based on existing lunar and terrestrial data sheds light on the role asteroid bombardments played in the geological evolution of the uppermost layers of the Hadean Earth.” “When we look at the present day, we have a very high fidelity timeline over the last about 500 million years of whats happened on Earth, and we have a pretty good understanding that plate tectonics and volcanism and all these kinds of processes have happened more or less the same way over the last couple of billion years … “But, in the very beginning of Earths formation, the first 500 million years, theres a less well-known period which has typically been called the Hadean (meaning hell-like) because it was assumed that it was wildly hot and volcanic and everything was covered with magma -- completely unlike the present day.” … “While researchers estimate accretion during late bombardment contributed less than one percent of Earths present-day mass, giant asteroid impacts still had a profound effect on the geological evolution of early Earth. Prior to four billion years ago Earth was resurfaced over and over by voluminous impact-generated melt. Furthermore, large collisions as late as about four billion years ago, may have repeatedly boiled away existing oceans into steamy atmospheres. Despite heavy bombardment, the findings are compatible with the claim of liquid water on Earths surface as early as about 4.3 billion years ago based on geochemical data.” … “Prior to approximately four billion years ago, no large region of Earths surface could have survived untouched by impacts and their effects …