Learn Italian: Lo scienziato ha scavato e ha trovato un fossile antichissimo. - The scientist dug and found a very ancient fossil.

You can use molto tempo fa (literally much time ago). You usually put these time expressions at the very beginning or the very end of the sentence. For example: Lo scienziato ha scavato e ha trovato un fossile antichissimo molto tempo fa.

Why is the article Lo used for scienziato instead of Il?

Because scienziato starts with an s followed by another consonant (c). Masculine singular words starting with s plus a consonant always take the definite article lo instead of il.

Why does antichissimo have an h in it when the base word is antico?

The suffix -issimo means 'very', turning antico (ancient) into antichissimo (very ancient). Because antico ends with a hard 'k' sound, you have to add an h before the i in -issimo to keep that hard sound. Without the h, it would be pronounced with a soft 'ch' sound like in 'cheese'.

Why do we repeat ha in ha scavato e ha trovato? Could I just say ha scavato e trovato?