| Age millions of years. Uncertainties not shown |
Period |
Selected Texas events |
Other relevant events |
Non-vertebrate activity |
| 1.8 |
Quaternary |
Beginning of Padre Island, the result of sea level rises due to melting glaciers. |
|
Marine invertebrates in the Gulf area. |
| 65.5 |
Tertiary |
Volcanoes form the peaks in Big Bend. Last movement of the Balcones fault zone during the Miocene. |
Damon mound corals develop on a salt dome. |
Reef building corals, many echinoids, snails, & clams. |
| 145.5 |
Cretaceous |
Marine conditions leave behind the limestones we see in Central Texas today. |
Pilot Knob undersea volcano. |
Ammonites, oysters, & rudists are abundant. Ammonites & rudists die out during the extinction at the Cretaceous-Tertiary boundary. |
| 199.6 |
Jurassic |
Opening of the Gulf of Mexico, salt pans develop. These rocks are exposed at the surface only in a few places in West Texas. |
Earliest flowering plants. |
|
| 251.0 |
Triassic |
Pangaea, the supercontinent of the time, begins to split apart. |
New ferns & cycads appear. |
Corals begin to expand in the west Texas marine areas. |
| 299.0 |
Permian |
Formation of big sponge & bryozoan reefs (the present- day Guadalupe Mountains). |
Ferns of all types decline. Early conifers appear. |
Brachiopods, corals, bryozoa, & crinoids decline during the Permo-Triassic extinction. |
| 318.1 |
Pennsylvanian |
Shallow marine environment with deltas in north Texas. |
Large fern forests leave thin coal beds. |
Snails, clams, crinoids, bryozoa, & trilobites in the marine areas. |
| 359.2 |
Mississippian |
Shallow seas, chaetetid mounds in the Llano region. |
Ferns abundant. |
Brachiopods, bryozoa, trilobites, & corals in the marine areas. |
| 416.0 |
Devonian |
Most marine rocks of this period are not exposed at the surface today. |
Ferns of all types develop in non-marine areas. |
|
| 443.7 |
Silurian |
West Texas shallow seas. Very few of these rocks are exposed at the surface today. |
First land plants. |
Rare occurrences of brachiopods & corals, although corals evolve rapidly during this time. |
| 488.3 |
Ordovician |
Limestone formed in shallow seas. This is an important source of hydrocarbons in West Texas. |
Algae/stromatolites occur around the Llano uplift. |
Corals & brachiopods in the Franklin Mountains near El Paso. |
| 542.0 |
Cambrian |
Shallow marine conditions spread over Texas. Outcrops of these rocks can be seen around the Llano uplift. |
Proliferation of life forms with hard ‘skeletons’. |
Trilobites roamed the seafloor, along with brachiopods, sponges, snails, & bryozoa. |
| 2500 |
Proterozoic |
Oldest exposed rocks in Texas, around 1.9 billion years ago. |
|
Some rare algae near the Cambrian boundary. |
| 4600 |
Archean |
|
Simple life forms found as early as 3.5 billion years ago. |
However, no such fossils have been found in Texas. |
